Takeuchi Hydraulic Excavator TB175W (S/N 17540001~). WORKSHOP MANUAL

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Overview of System Operation

• Truck and Heavy Equipment Systems

• Air Conditioner-System Operation

• Heater System Operation

• Environmental Effects on System Operation

• Chapter Review

Truck and Heavy Equipment Systems

A variety of HVAC systems are in use today, some old and some new. There are:

•

Vehicle manufacturer installed systems

• Owner specified systems

•

Add-on systems

• Retrofit systems

The system components come in different colors, shapes, and sizes. They may be

mounted in or on the cab in varied locations. Owners or fleet maintenance people

can  modify  systems  by  adding  controls,  auxiliary  units  or  ducts.  Major  compo-
nents are sometimes replaced due to damage or failure. All systems were, at least
originally,  designed  and  installed  to  meet  the  needs  of  an  operator.  Figure  2-1
includes  illustrations  of  various AC  and  Heater  systems.  They  illustrate  system
advantages and disadvantages explained in the paragraphs that follow.

The HVAC system includes both heater and air conditioner components, usu-

ally a common control, and air ducts. The system cools the cab by removing heat
energy. It removes moisture from damp air in the cab and adds fresh outside air to
the cab. In this way, the operator can work comfortably in all kinds of weather.

A sleeper unit, built in or added on, increases the air volumes in the cab. The

air conditioner or heater must circulate and cool or heat a larger amount of air.
This is accomplished by routing ducts and controls to the sleeper compartment as
part of system design. Components may be increased in size to handle the larger
cab air volume. A bigger heater core, air conditioning evaporator coil, condenser,
blower or fan may be included. Often, on long haul trucks, auxiliary air condi-
tioning and heater components and controls are added. The objective remains the
same, to move heat energy and maintain occupant comfort.

Click on any of these

subject headings to go

directly to the page

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Air Conditioner—System Operation

By law, all trucks have a heater/defroster as part of the standard equipment. When there
is a reason to add air conditioning, there are options to meet different needs. The avail-
able space in the cab, operating environment, and owner preference can all play a part
in the type of AC unit selected. You will probably encounter roof-mounted and in-cab
add on systems, and even systems where the condenser is mounted on the roof and the
evaporator is attached to the back panel or mounted under the dash. In cooler climates
you may come across a cab with two heaters, the original and an auxiliary unit.

Air Conditioner—System Operation

We  have  described  the  movement  of  heat  energy  and  basic  HVAC  system  function  in
Chapter  1.  Now  we  will  go  into  some  detail  on  how  an  air  conditioner  operates.  The
system is sealed to keep out air and moisture. To operate properly, the inside of the sys-
tem contains a measured amount of refrigerant and special refrigerant oil that keeps the
system  lubricated.  Figure  2-2  is  an  illustration  of  system  components  without  the  cab
outline, in-cab controls, component housing, and air ducts or vents. Please study it for a
moment. Note the information printed next to each component. Remember that the com-
ponents may be positioned and attached to the truck in various locations.

Figure 2-1

These illustrations show a
basic heater, HVAC system,
the combo system with
sleeper unit, add on AC roof
top and in cab units, roof
mounted condenser and
auxiliary units.

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System Operation

The following AC components are discussed in detail in this section:

1. Compressor/Clutch Assembly

2. Condenser

3. Receiver-Drier

4. Expansion Valve

5. Evaporator Coil

1. Compressor/Clutch Assembly

The  compressor/clutch  assembly  is  the  heart  of  the  system.  When  the  clutch  is
engaged,  the  compressor  pumps  refrigerant  and  oil  around  the  system.  It  raises
the temperature and pressure of the refrigerant gas, and forces it to the condenser
where it changes state and becomes a liquid. The compressor also sucks the va-
porized refrigerant out of the evaporator and back inside itself in the form of gas.
One  way  valves  inside  the  compressor  separate  the  compressed  gas  (high  pres-
sure) side of the system from the suction (low pressure) side. Figure 2-3 shows a
cutaway view of a compressor with the high and low pressure sides noted.

Figure 2-2

Air Conditioner components
are connected together to
illustrate system operation.
The components shown are
not to scale. The refrigerant
and refrigerant oil are clear
in color and not visible in
this drawing. The small ar-
rows inside the components
and connecting hoses show
the direction of refrigerant

flow (refrigerant circuit).

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Air Conditioner—System Operation

The clutch is mounted on the shaft of the compressor and is engaged by electromag-
netic action. Part of the clutch assembly is an electromagnetic wire coil. The coil is
energized through a thermostat that senses the temperature in the evaporator coil. If

the evaporator is too warm the electrical contacts close and allows power to flow to

the clutch. The compressor shaft is engaged and moves the refrigerant around inside
the system. Figure 2-4 is a cutaway view of the clutch mounted on the compressor.

2. Condenser

The refrigerant gas leaves the compressor and moves through a high pressure hose to
the condenser. Inside the condenser the gas “changes state” and becomes a liquid. It
is still hot and under pressure. Remember in Chapter 1 when we talked about water
at 212 degrees Fahrenheit? Heat energy was involved in the “change of state,” but
the temperature did not change. The same kind of action happens inside the AC sys-
tem. The refrigerant gas gives up a lot of heat energy to the outside air as it “changes
state” in the condenser. Figure 2-5 illustrates a condenser. Air moving through the

condenser absorbs heat from the refrigerant. The amount of air flow through the con

denser is the major factor in how well the condenser functions.

Figure 2-3

The compressor inlet is
low pressure and the outlet
is high pressure. The reed
valves are one way. They
open to allow refrigerant gas
to enter the compressor on
the down stroke and exit on
the upstroke. Note the open
valves in the illustrations.

Figure 2-4

The clutch shown here has
its electromagnetic coil
mounted on the compressor
body. When the coil is ener-
gized, magnetic force pulls
the clutch drive plate into
the pulley. This action locks
the pulley to the compressor
drive shaft and drives the
compressor.

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System Operation

3. Receiver-Drier

The liquid refrigerant continues to move inside the system, out of the condenser
through a tube or hose to the receiver-drier. The receiver-drier serves as a small stor-

age tank and filter for the refrigerant. It is also a good location to mount pressure

switches and often contains a sight glass (small window) used to view activity inside
the system. The receiver-drier, Figure 2-6, also separates gas (bubbles) from the
liquid with a pick-up tube as shown in this illustration. Some receiver-driers have a
spring to preload the desiccant pack.

Figure 2-5

As the refrigerant gas moves
through the tubing coil from
top to bottom, it condenses
(changes state) into a liquid.
For ease of installation,

condenser fittings are often

routed close together.

Figure 2-6

This cutaway view of a

receiver-drier shows the fil

ter elements, inlet, outlet and
refrigerant path. The sight
glass is a small window into
the system used in diagnosis
and when adding refrigerant
(charging the system).

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Air Conditioner—System Operation

4. Expansion Valve (Refrigerant Metering Device)

When refrigerant moves from the receiver-drier, it travels through another high pres-
sure hose to a metering device at the inlet of the evaporator coil. The metering device
can be an expansion valve, an expansion tube or a combination (multiple function)
valve. Between the compressor and this point inside the system, the pressure is high
and can range from 150 to 250 pounds per square inch. The expansion valve (TXV)
is closely connected to the evaporator. A diaphragm opens the valve by exerting pres-
sure on the spring. Pressure comes from gas inside the diaphragm housing on top of
the valve and in the sealed sensing bulb. The sensing tube is located in the outlet of
the evaporator and picks up heat from warm refrigerant leaving the evaporator. The
gas in the valve diaphragm housing and sensing tube expands when it gets warmer

and forces the expansion valve open at the metering orifice.

5. Evaporator Coil

The expansion valve or other type of metering device bleeds high pressure refrigerant
into the evaporator coil, where the pressure is low. The refrigerant expands rapidly in
this low pressure environment. When it expands it “changes state”. The sudden drop
in pressure brings the refrigerant temperature down quickly inside the evaporator
coil. Figure 2-8 shows an evaporator coil and thermostat. Refrigerant is sprayed into
the evaporator by the high side pressure when the expansion valve opens. The refrig-

erant absorbs heat from the air when the blower forces the air through the fins. When

the thermostat probe senses the upper limit of the thermostat heat setting, a circuit
closes. The compressor clutch engages and the compressor operates and moves more
refrigerant to the high side of the system.

Figure 2-7

This block type expansion
valve cutaway view will give
you a better idea how these
valves work. Spring pressure
holds the valve closed.

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System Operation

Note:

Moisture in the air (humidity) condenses on the fins of the

evaporator as water droplets which drain out of the evapora-

tor through a drain hose. This action dehumidifies the air in

the cab as part of system operation, and contributes to opera-
tor comfort.

Cab air forced across the evaporator coil gives up heat energy to the cold
refrigerant inside the coil. The cooled air circulates in the cab for occupant
comfort. Refrigerant continues to expand and absorb heat energy in the
evaporator coil. Refrigerant changes from liquid to gas before it leaves the
evaporator on the way back to the compressor. The refrigerant gas moves to
the compressor through a low pressure (suction) hose. When the compressor
is operating, it sucks the refrigerant gas back inside, compressing and rais-
ing its temperature and pressure.

Some of AC system operation is controlled by the operator, and some is auto-
matic. The operator can turn the system on and off, regulate the air velocity with
the blower control, and in some designs adjust the thermostat control. The system
and component operating range settings automatically cycle the clutch on and off.
The operation of the expansion valve or other refrigerant metering device at the
inlet to the evaporator is automatic.

Individual system features may differ, but the basic system function remains

the same. Variations in components and controls are described in Chapters 4 and
5. The engine provides the power for both air conditioner and heater operation. It
drives the AC compressor and the cooling system water pump. Engine RPM af-

fects the efficiency of both the heater and air conditioner. The slower the engine

RPM, the less capacity a heater or AC system will have.

When an AC system is operating, the high pressure side

components, fittings and high pressure lines or hoses can

be hot enough to burn your skin if you touch them. This in-
cludes  the  compressor,  clutch,  hoses,  condenser,  receiver-
drier,  and  any  control  devices  or  metal  tubing.  The  low
pressure  side  will  be  cool  to  the  touch.  In  operation  the
AC system is under load and high side pressures normally
range  between  150  and  250  pounds  per  square  inch  for
R-12 and higher for some other refrigerants.

Figure 2-8

The evaporator coil as shown

is of fin and tube construc

tion. The thermostat probe
is positioned in between the

evaporator fins and senses

the temperature.

WARNING

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Heater System Operation

Heater and air conditioner systems both have the same basic function of mov-
ing heat. They take advantage of nature’s laws where heat energy always moves
from a warmer to a cooler area. In a heater system there is no “change of state”
involved in system operation. The system is sealed and operates under pressure,
but the pressure is low when compared to an air conditioner.

A heater system uses the engine coolant to carry excess heat energy to the cab

air. The heart of the system is the water pump. The water pump forces hot coolant
through a hose from the engine block and through the heater core. The coolant is
returned to the engine cooling system either at the suction side of the water pump
or to the radiator.

A control cable, attached to a water valve between the water pump and the

heater inlet, is used to control the flow of coolant to the heater. The heater fan or

blower forces cab air through the heater core where heat energy moves from the
engine coolant to the air in the cab. Figure 2-9 illustrates the main heater system
components. In-cab controls, component housing and air vents are not shown.

The following heater components are discussed in detail in this section:

1. Heater Core

2. Water Valves

3. Defrosters and Ducts

4. Blowers and Fans

Additional heater controls, ducts, air vents, blend-air doors, temperature regu-
lating devices and auxiliary heaters may be installed as part of a heater system.
These may be air, vacuum, electrical or mechanically operated.

System Operation

Figure 2-9

This view of a heater system
shows the main components
and how they are connected.

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1. Heater Core

Heater cores are like small radiators. The fin and tube construction is de

signed to route coolant flow for the best possible heat energy transfer from

coolant to cab air. Hoses from and to the engine are connected to the core
with clamps. The core outlet may be larger or the same size as the inlet.

2. Water Valves

Water valves may be cable, vacuum or air controlled. The valve can be ei-
ther open, closed or set part way open. Some valves have a bypass design
to return coolant to the engine. Most are manually controlled although elec-
tronic systems are now being installed.

3. Defrosters and Ducts

Defrosting is accomplished by directing heated dry air through ducts to the
windshield. The heater system serves the dual purpose of defrosting and

heating. Controls are used to route the air flow to the windshield and occu

pant areas by opening and closing duct doors. Controls may be manual, air
or vacuum.

Many vehicles use a “defrost interlock” system which utilizes the air con-

ditioner to dry the defrost air and clear the cab windows more quickly.

4. Blowers and Fans

Blowers or fans are used in the system to move cab air through the heater
core and evaporator. Air can be pushed or pulled through the core depending
on system design. Blower or fan speed is usually selected by the operator.

Environmental Effects on System Operation

The environment outside the cab involves more than the weather. It may be hot
and humid or cold and dry. That is only part of the condition the HVAC system

must handle to maintain an ideal comfort range. A truck can be at idle, in traffic

or moving along for hours on the Interstate at 65 M.P.H. The load condition on a
trip can include going out full, coming home empty, or driving across the Rockies
or Kansas plains during the day or night. The truck color and shape, the windows
and angle of the sun are all variables that can increase or decrease the “load” on
the system. The following are a few examples of environmental effect:

• A black cab-over (COE) with a dark color interior will be more

difficult to cool than the same vehicle with white paint and a light

colored interior. The black cab picks up and holds the radiant heat
from the sun more easily than the white one.

• In Florida or Houston the humidity in mid summer can be very

high with the temperature in the high 90’s or low 100’s. The AC
unit must remove a lot of moisture from the air in the cab as the air

moves through the evaporator fins. The more moisture on the fins,

the less effective the transfer of heat is to the refrigerant inside the
evaporator coil.

Environmental Effects

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• On a cold day the temperature can drop below zero. The engine may

run cooler so the engine coolant is cooler when it circulates through
the heater. The heat in the cab moves out of the cab faster (remember
heat always moves to a cooler area until both are the same tempera-
ture—nature’s law). To maintain cab comfort you have to increase the

flow of coolant through the heater, increase coolant temperature, and/

or move more air through the heater core.

• On a hot day, an off-road vehicle experiences cooling at a slower rate

than an on-road vehicle. This is a result of high sun-load, large window
area and often less insulation.

It is important for you to keep environmental effects in mind when you are servicing
or diagnosing heater or air conditioner systems. If you work in Denver the altitude
will affect system function and pressure. In Houston the heat and humidity may lower
heat transfer to the air at the condenser and increase system operating pressures.

Chapter Review

• HVAC systems range from simple cab heaters to multi-function com-

bination systems. The multi-function system can heat and cool the cab
and sleeper unit, and have separate auxiliary components and controls
for driver and passenger comfort.

• Both heater (engine) coolant and air conditioner refrigerant circulate

inside sealed, pressurized systems. The normal air conditioner operat-
ing pressure ranges from 150 to 250 pounds per square inch, some-
times higher with a different refrigerant.

• Air conditioners have a high and a low pressure side within the system.

The compressor is the starting point of the high side. Pressure drops at
the expansion valve opening to the evaporator.

• The basic components of an AC system are the compressorclutch as-

sembly, high pressure lines, condenser, receiver-drier, expansion valve,
evaporator, thermostat, blower assembly, and suction lines. There may
be other controls installed for more complex systems.

• The basic components of a heater system are the inlet and outlet hoses,

a water valve and valve control, heater core and fan or blower assem-
bly. There may be other controls for more complex systems.

• An air conditioner system uses the “change of state” of refrigerant in-

side the system to move heat from the cab air to the outside air. Refrig-
erant changes from a gas to a liquid in the condenser, and back to a gas
in the evaporator.

• A heater system uses the heat from the engine, carried to the heater

core by the action of the water pump, to warm the air in the cab. There
is no change of state within the heater system.

• Environmental conditions affect how both heaters and air conditioners

work. Weather, driving conditions, color of the vehicle are factors. All
contribute to heat gain or loss inside a cab and how much heat energy
must be moved to maintain occupant comfort.

System Operation

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Inspection and Maintenance-
without gauges

• Discussion of Inspection & Maintenance Survey Results

• Visual Inspection - System Off

• Electrical System Inspection

• Performance Inspection - Engine Running

• Heater System Inspection

• Preventive Maintenance Worksheet

• Chapter Review

Discussion of Inspection & Maintenance Survey Results

There are three reasons for regular inspection and maintenance procedures:

1. They save money in the long run by reducing down time and often

prevent more costly repairs.

2. They help to insure driver comfort and safety.
3. They add to your store of knowledge about these systems and main-

tain your level of efficiency.

About half of all heavy duty vehicles have air conditioners. Surveys of AC system

owners find that over 30% of the systems are serviced every six months or less,

and another 62% are serviced at least once a year.

The survey also covered how often the different components required mainte-

nance. Figure 7.1 below shows survey finding percentages. Failure of any of the

AC components listed in the survey could cause a system to malfunction or stop
cooling.

INSPECTION & MAINTENANCE SURVEY

Note: The above survey results may not apply to your situation. Ac-

tual operating conditions for the vehicles you service will de-

termine or influence maintenance frequency and requirements.

The following inspection procedures should take about 15 to 20 minutes, longer
if corrective steps, part replacement or adding refrigerant is necessary. There is
a “Preventive Maintenance Worksheet” you may use at the end of this chapter,
Figure 7-9

Click on any of these

subject headings to go

directly to the page

Figure 7-1

This chart shows mainte-
nance frequency, lists key
parts and how often they
require maintenance.

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Visual Inspection - System Off

Your observations and the corrective measures you take may be different depend-
ing on circumstances. The following inspection procedures are explained in more
detail below:

1. Observe the System

2. Inspect Parts

3. Check Hoses and Fittings

4. Check for Refrigerant Leaks

Use the following procedures as a general rule in performing a visual inspection
with the AC system off:

1. Observe the System

Your first inspection step is to answer the following question if you can:

• Has the vehicle just come in off the road and has the HVAC

system been in use?

• Did the operator or work order explain or describe any prob-

lems about the system?

• Did someone else work on the system yesterday, 700 miles

down the road? Your first inspection step is to answer these

questions if you can.

Even  when  someone  has  told  you  what  is  wrong  with  an
HVAC  system,  you  should  perform  a  visual  inspection.
Always  make  a  visual  inspection  before  you  hook  up  the
manifold gauge set. Never add refrigerant to a system until
you have made a complete visual and performance inspec-
tion.

2. Inspect Parts

Look at the system for what might come loose, leak, wear out or become
dirty and not function the way it should. The main points for visual inspec-
tion of the system are emphasized in Figure 7-2.

Inspection & Maintenance

CAUTION

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A. Condenser – Is it free of leaves, bugs, bird feathers or mud? The con-
denser must be relatively clean to work well as a heat exchanger. How you

clean the condenser depends on where it is mounted. The condenser fin

comb, air hose and nozzle, or soap and water may be used. Where possible,
check condenser mounting bolts or screws and tighten them if necessary.

Condenser failure often results from loose hoses. Hose movement will

cause fatigue failure of condenser tubing adjacent to the fittings. Make sure

the hoses are securely clamped.

While inspecting the condenser check the receiver-drier sight glass and

connections. Look to see if the sight glass has a moisture indicator that is
showing moisture in the system.

B.  Components Under the Hood – Tip the cab or raise the hood. Look at
the  compressor  mounting  bracket,  compressor  clutch  assembly,  drive  belt
and  pulley  alignment. The  mounting  bracket,  compressor,  clutch  and  drive
pulley  should  be  fastened  securely,  and  a  clutch  groove  (there  may  be  two
groves)  should  be  in  line  with  the  drive  pulley.  Tighten  all  bolts  shown  in
Figure 7-3, as you inspect.

Visual Inspection

Figure 7-3

Engine and compressor
vibration can work mount-
ing bolts loose. Tighten all
mounting bolts as you in-
spect the system. Slots in the
mounting bracket are used to
move the compressor clutch
assembly in order to adjust
belt tension or alignment.

Figure 7-2

This system illustration notes
the main points for visual
inspection.

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C. Drive Belt – The drive belt should be tight and in good condition. Use
a belt tension gauge to check tension (120 pounds maximum). With experi-
ence, you can feel belt tension by twisting the belt. Try feeling belt tension
after using the gauge, when you know the tension is correct. Replace belts if
they are frayed or look worn.

If the clutch pulley/belt alignment is obviously off, you need to loosen

the compressor or mounting bracket, or both—and use the alignment bar to
line up the clutch pulley with the drive pulley. Tighten compressor mounting

bolts first, then the bolts holding the bracket. The mounting bracket should

have slots or other means of adjustment to allow you to adjust the tension of
the drive belt. When you use a pry bar to apply tension, be sure you do not
pry against the compressor. Pry against the mounting bracket.

3. Check Hoses and Fittings

Check all hoses and fittings. Look for places where hoses flex when the cab is

tilted. Any places the hoses or fittings are fastened, clamped, connected, bent or

secured are potential wear points. This also applies to places where hoses are not
clamped or supported but should be (often near the condenser). All of these spots
are potential leak or damage points. Tighten, re-fasten, add, or replace as indi-
cated by your inspection.

4. Check for Refrigerant Leaks

System refrigerant leaks can be anywhere but there are obvious places. You can
spot some by looking for signs of refrigerant oil forced out with refrigerant leak-
age.  One  location  leaks  frequently  occur  is  the  compressor  shaft  seal. The  shaft
and seal are hidden behind the clutch assembly, but centrifugal force will throw
the oil  off the shaft  and  against  the  engine,  bracket or  whatever  is  close.  Check
these  points  when  you  examine  the  compressor  clutch  and  mounting  bracket. A
solution  of  soap  and  water  applied  around  potential  leak  points  works  well  for
detecting leaks. A leak in the evaporator may be indicated if you feel around the

condensate drain hole and find oil present.

Note: You can add inexpensive dry nitrogen gas to the system instead

of R-12 if system pressures are low. Dispense the gas at no more

than 200-250 PSI as this is sufficient pressure to cause or indicate

a leak point in the AC system. AC service procedures for complete
system recovering of refrigerant, evacuating, and recharging are
covered and illustrated in Chapter 9.

Note: A leaking heater core could also result in coolant at the condensate

drain.

Inspection & Maintenance

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You can feel for oil at the bottom of all connections (see Figure 7-4) if the
system is not too hot. Of course, a few minutes with an electronic leak de-
tector is the best way to check for leaks. Keep in mind that pressure is dif-

ferent in a system at rest, so small leaks may be hard to find. Pressure in a

system at rest, will equalize at from 60 to 95 PSI, depending on outside air
temperature. This means there is more pressure in the low side of the system
at rest than during normal system operation. Just the opposite is true of the
high side; at rest, high side pressure is lower. You may want to use the detec-
tor to check for leaks in the high side when the air conditioner is operating,

if you suspect a leak and can’t find it when the system is at rest.

Electrical System Inspection

The two stages of an electrical inspection are explained in more detail below:

1. Inspect Electrical Connections

2. Check Electrical Current Flow and Device Functions

Use the following procedures to perform an electrical system inspection:

1. Inspect Electrical Connections

First, while you are making your visual inspection under the hood (cab)
and/or at the roof top condenser, take a moment and check all electrical con-
nections visually and by feel. Look for any corrosion on leads or connectors
and clean them. Make sure all leads and wires are properly supported and
securely connected.

2. Check Electrical Current Flow and Device Functions

Perform the following steps to check current flow and electrical device func

tions:

A. Turn the Ignition On

– To check current flow the ignition must be

on.

Electrical System Inspection

Figure 7-4

This illustration shows a po-
tential refrigerant leak point

at the condenser fitting.

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B.  Turn  the  AC  System  On  –  This  will  power  the  thermostat  and
clutch.  If  it  does  not  come  on,  use  the AC  mode  switch  to  check  the
leads to the switch. You should be able to hear a “click” from the ther-
mostat  and  hear  the  clutch  drive  plate  “snap”  against  the  clutch  pul-
ley. You can not check thermostat cycling on and off until you do the
performance  inspection.  Figure  7-5  illustrates  a  typical  AC  electrical
system and the places you should inspect.

C. Check Fuses – If there is a failure and you have made sure all con-
nections are clean and tight, you need to check fuses—in-cab as well as
in-line.

D. Check Clutch Engagement – Since you can’t see and may not hear
the clutch engage, get out and look at the clutch. If it’s engaged, you
will see that the drive plate is against the pulley and not slightly spaced
from it. If you are not sure the clutch is engaged, look for the lead wire
connector near the clutch. Break and close that connection. The clutch
will disengage and engage again.

E.  Test  Blower  Speed  Operation  –  Some  systems  have  a  common
switch  that  turns  on  the  air  conditioner  and  powers  the  blower  motor.
Test  blower  speed  operation  by  adjusting  this  or  the  separate  blower

control switch. Feeling the air flow from the ducts or note blower

sound (speed) changes.

F. Inspect Roof Mounted Condensers – Don’t forget to inspect roof
mounted condensers and AC systems for dirt and debris. Be sure the
condenser fan(s) are working properly and all parts and electrical con-
nections are securely fastened. The roof mounted condenser fans may
come on when the system is turned on. Like the thermostat and most
clutches, the normal on-off cycling action can not be observed until the
engine is running with the AC system on.

Inspection & Maintenance

Figure 7-5

The electrical system inspec-
tion points are noted with
check marks (

✔

) on this

wiring diagram (electrical
schematic).

Takeuchi Hydraulic Excavator TB175W (S/N 17540001~). WORKSHOP MANUAL - page 6