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These readings at the vents will be higher and temperature swing slower
and not as obvious. Also blower speed will cause the temperature, levels
to read higher (high air speed) or lower (low air speed) at the same
thermostat setting. When you measure air temperature, an electronic
thermometer/pyrometer is a great tool to have. You can easily measure
cab air temperature at several locations quickly.

Swing temperatures vary depending on where you measure tempera-

ture, and on outside temperature, humidity and altitude. The chart in
Figure 7-6, shows some examples of typical temperature variables. Don’t
forget that cab and sleeper area temperatures can vary within the same
vehicle. Also, electronic controls used in newer HVAC systems often
keep the temperature spread within a narrower range.

2. Check Clutch Cycling Under Load

The following operating inspections, visual and by feel, are done outside the
cab while you wait for the system to stabilize.

A. Lift hood

– With the hood up (or cab tilted) observe the clutch cycling

under load.

Note:

If the condenser is hood mounted you may not have adequate air
flow through it.

B. Touch suction and discharge lines

– Soon after system start up you

can safely feel the suction and discharge lines and note their change in
temperature. The discharge line will get hot (after a while it may be to hot
to touch) and the suction line will get cooler.

3. Check Sight Glass

The sight glass is the only point where you can actually see inside the air
conditioner during operation. Check the sight glass through the window on the
top of the receiver-drier (or the separate in-line sight glass). If the system is
functioning properly and cooling the cab adequately, the sight glass should be
clear (you will not see anything in it). If it is not clear when the system is first
turned on, wait a few minutes for the system to stabilize, then look again. Figure
7-7 illustrates and explains what you may observe in the sight glass. Roof
mounted condenser fans may run continuously or cycle on and off. If you can’t
tell by sound you may have to climb a ladder and observe the fan blades.

Inspection & Maintenance

Figure 7-6

The chart of AC system and
cab temperature range shows
you typical variables.

AIR TEMP.

DEGREES F.

AIR QUALITY

CENTER OUTLET

AIR TEMP.

DEGREES F.

OUTLET AIR TEMP.

RANGE DEGREES F.

HUMID

100

DRY

LEFT & RIGHT AIR OUTLET TEMPERATURE WILL VARY

LEFT

RIGHT

LEFT

RIGHT

LEFT

RIGHT

LEFT

RIGHT

HUMID

DRY

HUMID

DRY

HUMID

DRY

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Note:

A roof mounted condenser or AC unit assembly often includes
a roof mounted receiver-drier (and sight glass) close to the
condenser.

Heater System Inspection

A heater system inspection is really a combination engine cooling system and heater
inspection. All heater/cooling system rubber parts deteriorate due to the air (ozone),
heat, coolant and oils. They should be replaced at regular intervals to prevent
breakdown on the road. Metal parts and gaskets are subject to malfunction or
breakdown due to fatigue and corrosion.

Coolant has a limited life and should be replaced regularly. If it is dirty, the cooling

system should be drained and flushed or back flushed (using special equipment)
before refilling with clean water and anti-freeze. Coolant must be hot when using the
hydrometer to check protection (freeze-up) level. The following inspection proce-
dures are explained in more detail below:

1. Check Heater Control Valve Function

2. Inspect Other Functions

1. Check Heater Control Valve Function

Many air conditioner/heater systems depend on the heater control valve for
temperature control and positive closure. You can easily check heater control
valve function as follows.

A. Cool engine

– Start with the engine cool, set the temperature to cold

and leave the fan off. As the engine warms up, feel the heater return hose.
If the hose feels warm or hot, the heater control valve is leaking internally.
This type of leak can seriously reduce air conditioning performance.

Performance Inspection

Figure 7-7

These drawings illustrate
conditions you may observe
in the sight glass window.

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B. Warm up engine

– Next, let the engine warm up to normal operating

temperature and set both fan and temperature on high. Feel both heater
supply and return hoses. If there is a noticeable difference in their
temperature, it indicates a low flow of coolant through the heater core (a
partially closed or blocked heater control valve). This could result in poor
heating performance during cold weather conditions.

2. Inspect Other Functions

There are some things you can’t see or feel when you inspect the thermostat,
heater core, radiator pressure cap, electrical switch and control valve functions.
Some of these can be checked with the pressure and thermostat testers as
described in

Chapter 6

. A hand pump pressure tester can also be used to check

for coolant leaks. This is done by using the pump to raise the pressure inside the
system above normal operating pressure to force small suspected leaks to show
up.

Heater/cooling electrical and valve component inspection is the same as air

conditioner inspection. The controls are operated to see if they function
correctly to maintain or vary cab temperature and air flow.

Preventive Maintenance Worksheet

Please feel free to modify or copy the worksheet in Figure 7-9. Actual vehicle use,
mileage, operating conditions and maintenance budget may influence service
frequency.

Inspection & Maintenance

Figure 7-8

Heater/cooling system
potential problem areas and
checks are indicated in this
drawing.

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Chapter Review

The purpose of these brief inspection procedures is for vehicle system maintenance
and to determine if further, more detailed service is required. The uses of a manifold
gauge set, system troubleshooting, recovery, flushing, evacuating and charging are
explained in the next chapter.

High usage and operating condition variations are tough on air conditioning and

heater components. You should establish and follow regular inspection and mainte-
nance procedures to improve overall system function and component service life.

The typical inspection should not take more than 15 to 20 minutes unless

component replacement and/or complete system evacuation and recharging is
warranted. The survey results shown in Figure 7-1, indicate belts, compressor clutch
assembly, condenser and the refrigerant lines are the most frequent problem areas.
However, your own experience with service and maintenance may vary from survey
results.

Inspection should first be visual and by feel. Some of your electrical system

inspection will be done as you inspect other components (checking leads, connec-
tions and for loose wires). When you check the electrical circuit, begin with the
engine off but ignition on. A system performance inspection with the engine running
and system on really combines electrical and AC or heater system function.

Chapter Review

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Troubleshooting
& Service Procedures

• Troubleshooting Overview
• Understanding System Function
• A Troubleshooting Example
• Manifold Gauge Set Installation
• Troubleshooting by Manifold Gauge Set Readings
• Review of Frequent Problem Areas
• Conclusion

Can you fix an air conditioner or heater system without finding and correcting
the cause of the problem? You bet you can!

It happens every day and it’s not good

for business. Here is an example. A truck pulls in off the road and the operator asks
to have his rig serviced in a hurry. He tells you the air conditioner isn’t cooling like
it should and dashes into the restaurant for lunch.

You tip the hood, and check the sight glass on top of the receiver-drier. You see

bubbles, not a lot but a fairly constant stream of them. It is obvious the system is low
on refrigerant so you hook up the manifold gauge set, purge the gauge set hoses of
air, and add refrigerant until the sight glass clears. Then you check evaporator
temperature and it’s OK.

The air conditioner is repaired right?

Wrong! What you

did is add refrigerant and the problem went away. You did not find and fix the cause
of the problem.

Component failure in an air conditioning system may be the result of a problem

elsewhere in the system. For example, a belt or clutch failure might be caused by a
dirty condenser restricting air flow and increasing head pressures. High head
pressures commonly create problems with other system components.

Take time to

look beyond the obvious for a potential hidden problem

Troubleshooting Overview

Troubleshooting includes collecting enough information to locate the cause of the
problem, then correcting the problem and its cause by replacement, adjustment, and/
or repairing. You begin by gathering information from the most to the least important
sources.

Starting with the most important:

Your personal knowledge and experience with AC systems.

The vehicle operator's knowledge and experience—question him or her.

The work order.

Good test equipment and the HVAC system

The routine you follow when troubleshooting should proceed from the most to least
productive way of locating the problem and fixing the cause.

Click on any of these

subject headings to go

directly to the page

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Experienced troubleshooters talk to the operator if they can, then personally verify
the symptoms of the problem whenever possible. They attempt quick fixes on the
basis of their knowledge of common system problems and causes when appropriate.
They know where components are located, and make repairs when they have a good
idea of what the problem is. They fix the cause or causes as well as the problem. They
are confident of their knowledge and ability.

Note:

The best troubleshooters all know who to call when they get
stuck.

They know someone who knows more than they do and

are not too proud to ask for help or suggestions when needed.
The key—understanding system function

The Key–Understanding System Function

Your complete understanding of AC and heater systems and how they work,
plus what can go wrong, is the key to troubleshooting and repair.

We have talked

about components and system function before. Now let’s take a little different
approach in describing what happens when the air conditioner is turned on. In Figure
8-1 we have used numbers on the illustration to track normal air conditioner function.

Troubleshooting & Service Procedures

Figure 8-1

An illustration of the typical
HVAC system. The numbers
follow the action when the
AC part of the system is
working properly (moving
heat out of the cab and into
the outside air).

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When you turn on the air conditioner at the control panel (1), the thermostat (2), is
supposed to sense a warm temperature at the evaporator. A circuit in the thermostat
should close, allowing current to flow through the thermostat to the compressor
clutch field coil (3). When this happens, the clutch field coil becomes an electromag-
net and pulls the clutch drive plate (4) tight against the clutch pulley (5).

Note:

The same AC switch (1) may also turn on the fan or blower
motor (2a) to circulate air in the cab. The air feels warm at first
but will cool quickly.

A belt connects the clutch pulley to a drive pulley (6) on the engine. The engine
provides the power to turn the clutch pulley and drive the compressor (7) when the
clutch is engaged. When operating, the compressor compresses and pushes refrig-
erant gas to the condenser (8), through the receiver-drier (9), and to the expansion
valve (10) orifice. When it does, it puts a lot of pressure on the gas. The compressor
raises the temperature and pressure of the refrigerant inside the high side of the
system.

At the same time, the compressor is also sucking in low pressure refrigerant gas

from the expansion valve orifice, evaporator and through the low side of the system.
The movement of the refrigerant inside the system transfers heat energy from the cab
to the outside air for occupant comfort.

The automatic functions of the thermostat (or the pressure valve on some

accumulators), and the expansion valve, help maintain pressures and temperatures
inside the system at safe and efficient operating levels. Pressure and temperature are
constantly changing due to compressor and expansion valve action, the amount of
heat energy being moved and the environment or weather conditions.

The engine cooling system fan and clutch (11), and the evaporator blower motor

(2a), move a sufficient amount of air through the condenser and evaporator. On the
road, vehicle speed provides most of the (ram) air required for the condenser to work
right. In a parked or slow moving vehicle the engine fan (or roof or remote mounted
condenser and fans) moves sufficient air through the condenser fins.

Note:

Clean refrigerant and refrigeration oil should be inside the
system in the amount specified by the manufacturer. Moisture,
sludge (moisture combined with refrigerant oil or desiccant), or
desiccant particles will prevent the correct performance of the
system and may cause component damage.

A Troubleshooting Example

Remember the story at the beginning of this chapter? The vehicle operator pulled in
off the road and asked you to repair the rig. He was in such a hurry he didn’t tell you
anything except that the air conditioner wasn’t cooling. Here is the best way to handle
that kind of situation.

Understanding System Function

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Use your knowledge and experience. Ask yourself what could have caused a lack of
cooling in that rig! Did the compressor drive belt break? Did a pressure switch or
relief valve cutout the compressor because of high or low system pressure? Does the
switch or valve in this type of system reset itself? Could there be a superheat switch
and thermal limiter with a melted fuse. Did someone else service the system recently
and put in too much refrigerant?

Could there be contaminants in the system blocking the expansion valve (expan-

sion tube)? If there is a leak, why and how did refrigerant get out of the system? You
know if refrigerant can get out, air and moisture may get inside as well, especially
if the leak is on the suction side of the system. Could there be a restriction to
refrigerant flow in one of the high pressure lines because of a kink? From your
knowledge and experience, you already know about these possibilities and others
when you talk to the operator (before he has the chance to leave).

The right kind of questions can speed up troubleshooting and your service work

by pinpointing the problem(s) that needs fixing. Your conversation with the operator
might be as follows:

• How long ago did the AC system stop cooling?

Answer:

About an hour ago.

• What steps did you take when you noticed the lack of cooling?

Answer:

I put it on maximum cool.

• Then what did you do?

Answer:

When it wouldn’t cool, I opened the window and

turned the air conditioner off.

• Is this problem new or has it happened before, and when?

Answer:

In the last few days I’ve had problems with cooling off

and on—this is the first time it’s happened when I was close to
a place that did AC service.

• Do you get any cooling at all?

Answer:

Yes but it seems to quit after a while.

• Do you still get air flow at the vents from the blower?

Answer:

Yes.

• When was your air conditioner checked thoroughly?

Answer:

Before I bought the rig last May (a year ago).

• Has the heater been used recently and did it work OK?

Answer:

Yes.

Troubleshooting & Service Procedures

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• Have you had other service problems in the last few months?

Answer:

No.

• (If the answer was yes, you should ask—When? Where?

What was fixed or replaced?).

• Finally, ask the operator if he or she has a wiring diagram for the

system.

Now let’s look at the information you have gathered from the operator and what you
know from experience. He believes the problem is that the AC system quits cooling
after it has been on for a while! You know that the AC system has not been maintained
since the rig was purchased a year ago. Because of that, there could be several causes
for the problem (lack of cooling) and there may be other potential problems about
to develop.

It is possible that some refrigerant has leaked. Moisture and other contamination

may be inside the system. You have been told there are no heater problems, but that
doesn’t mean there are none that might affect AC system operation. The AC system
has quit cooling several times in the last few days. The problem may have become
more severe than when it quit cooling the first time.

If enough refrigerant or oil has leaked out, a low pressure cutout switch may have

cut the circuit to the clutch, protecting the compressor. Because the system has not
been maintained in a year, there may be other components that should be serviced.
You could fix the probable causes, and the system might work and then break down
again as the rig drives out of your place. From your knowledge and what the operator
has just told you, you know this may not be a quick fix problem.

It’s up to you to describe the service situation to the operator. Tell him you need

to do a complete system maintenance inspection to find and correct the problem or
other potential problems. He can give you the go ahead for full service and repair
now, wait till you have inspected the system to determine cause and cost, or delay
repair until he has some down time available.

Normally when the operator can tell you what the problem is, you would first

operate the system to verify the problem. In this situation your troubleshooting (your
own knowledge added to what the operator told you), indicates the next step. You
need to do a complete maintenance inspection instead! Proceed as described in

Chapter 7

. Correct any obvious problems and check carefully for leaks. Leak testing

should be visual, by feel and with a leak detector. Next, do your performance test with
the engine running and the AC system on.

Note:

Don’t forget to check the heater system too! If the water valve
is not closed, then hot engine coolant flowing through the heater
core would warm the air at the same time the evaporator was
trying to cool it. The result would be the appearance of an AC
problem.

A Troubleshooting Example

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If your AC and heater visual, electrical and leak inspections don’t turn up any
problems, save time by hooking up the manifold gauge set before you make the
performance test. If you find a leak and can correct it easily by tightening a
connection, do so. But if too much refrigerant leaked out, you may have to add some
refrigerant to the system for an effective performance test. We will get into detail on
troubleshooting with gauges after we explain manifold gauge set installation and
adding refrigerant.

Manifold Gauge Set Installation

Never hook up the gauge set when the engine and air
conditioner are running. Be sure all the valves on the mani-
fold are closed all the way (turn them clockwise). Check the
hose connections on the manifold for tightness.

Locate the low and high side system service fittings and remove their protective caps.
Position or hang the manifold gauge set in a convenient location. Figure 8-2
illustrates a good example of manifold gauge set hookup in one service situation.

The manifold gauge set is a necessary tool in troubleshooting AC system problems.
The following steps are performed during and after installing the manifold gauge set:

Purging Air from the Gauge Set Hoses

Adding Refrigerant to the System

Stabilizing the AC System.

Troubleshooting & Service Procedures

CAUTION

Figure 8-2

A typical manifold gauge set
hookup is shown in this
illustration. The center hose
on the gauge set is con-
nected to the vacuum pump.

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1. Purging Air From Gauge Set Hoses

Environmental regulations require that all service hoses have a shutoff valve
within 12 inches of the service end. These valves are required to ensure only a
minimal amount of refrigerant is lost to the atmosphere. R-12 gauge set hoses
have a valve near the end of all three hoses. R-134a gauge sets have a
combination quick disconnect and shutoff valve on the high and low sides. The
utility (center) hose also requires a valve.

The initial purging is best accomplished when connected to recovery or

recycle equipment. Figure 8-3 illustrates the gauge set connections for purging
and refrigeration recovery.

Note:

The manifold gauges read system pressure when the hand
valves are closed if the hose end valves, and the stem type
service valves (if included) are open.

2. Adding Refrigerant to the System

Now that the gauges are connected, you may need to add some refrigerant to the
AC system before you can do an effective performance inspection. However,
if leaks are obvious they should be repaired prior to adding refrigerant.

Note:

Loss of some refrigerant is not unusual over an extended period
of time. Adding refrigerant is a typical procedure when the AC
system is maintained on a regular basis.

When adding refrigerant to the system, connect the center hose from the
manifold gauge set to the refrigerant dispensing valve on the container. Figure
8-4 illustrates this connection.

Manifold Gauge Set Installation

Figure 8-3

The purging setup for
manifold gauge set and
compressor service valves
are shown here.

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Before adding refrigerant to the system you should study the sight glass while
the engine is running and the air conditioner is on. Even if you found a leak
during the system inspection and corrected it, you have no way of knowing how
much refrigerant has leaked. You will not be able to tell how much refrigerant
is in there, but you can see if bubbles are present.

Then check the gauges for unusually high or low readings, or a lack of

pressure. Following this procedure, and using your knowledge and experience,
decide if it is safe and makes sense to add refrigerant in order to make your full
performance inspection.

You are now ready to add refrigerant to the system. For your safety and to

prevent system damage use the following procedure.

Turn on the engine and set the idle at 1200 to 1500 RPM and then
turn on the air conditioner.

Do not open the high pressure hand valve on the manifold
gauge set. The compressor could pump refrigerant into the
container and cause it to BURST. Be sure to keep the
refrigerant container upright to prevent liquid refrigerant
from entering the compressor.

Open the refrigerant dispensing valve on the container and then the
low pressure hand valve on the manifold. This allows refrigerant to
enter the system as a gas on the low pressure or suction side of the
compressor. The compressor will pull refrigerant into the system.

Troubleshooting & Service Procedures

CAUTION

Figure 8-4

In this illustration we have
noted how refrigerant is
added to the air conditioner.

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Add refrigerant until the gauges read in the normal range and the
sight glass appears clear. The sight glass may not be clear for a
moment just before or after the clutch cycles on and off but should
generally be clear. Gauge readings will fluctuate as the compressor
cycles on and off.

Note:

Pressures within the air conditioning system vary with ambient
temperature. A normal pressure range is defined as follows:

Low side

15–30 PSIG

High side

150–280 PSIG

If R-134a is used in place of R-12 the high side readings will be
about 20 PSI higher. For this reason many OEMs are recom-
mending an increase in condenser capacity when retrofitting to
the new refrigerant, R-134a.

If the gauges show any abnormally high or low pressures as
you are adding refrigerant, stop and investigate for probable
cause. Never add more than one pound of refrigerant. If the
system is low enough on refrigerant to require more than that
amount you should stop and check again for leaks. Then
recover all of the refrigerant, repair, evacuate and recharge
the air conditioner. (See

Chapter 9

). You may want to add dry

nitrogen gas to the AC system instead of R-12 if pressures are
below normal and a leak is suspected. Nitrogen gas is sold in
cylinders under high pressure, 1800 to 2000 PSI. Be sure the
cylinder has a pressure regulating valve to control the pres-
sure when dispensing nitrogen gas. Dispose the gas at no
more than 200-250 psi, as this is sufficient pressure to cause
or indicate a leak point. See note under

Troubleshooting by

Manifold Gauge Set Readings

in this chapter.

When the gauges show normal, close the hand valve on the
manifold, the hose end shutoff valve, and the valve on the refriger-
ant container. You can now proceed with the performance inspec-
tion.

3. Stabilizing The AC System

For reliable gauge readings as an aid in troubleshooting, the AC system must
be stabilized.

Be sure your tools and test equipment are clear of all moving
parts of the engine and air conditioner.

Manifold Gauge Set Installation

CAUTION

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Start the engine and set to a fast idle of 1200 to 1500 RPM. Turn on the air
conditioner. After a quick in-cab performance test of control function, blower
speeds and air flow, set the AC system controls to maximum cooling and blower
speed on high. All windows must be closed. If cab temperature is hot (rig has
been sitting in the sun with the windows closed), open the windows for a minute
or so to let the hot air out. Run the engine and air conditioner about five minutes
for the system to stabilize. In hot humid weather or where the AC condenser
can’t receive adequate air flow from the engine fan you may have to use a floor
mounted fan to force sufficient air flow through condenser fins. This helps to
stabilize the system by simulating ram air flow found under normal operating
conditions.

When a vehicle has a tilt cab or hood and the condenser is part of the grill,

you must use the floor fan to get air to the condenser. You could tilt the cab or
hood back to normal position, carefully routing the manifold gauge set and
hoses away from moving parts. Then place the gauges so you can read system
pressure.

Troubleshooting by Manifold Gauge Set Readings

The series of figures that follow (Figures 8-6 through 8-15) show gauges with typical
readings indicating AC system problems. Each figure is followed by troubleshooting
tips, probable causes for the gauge readings shown, and appropriate service and
repair procedures.

Low Refrigerant Charge in the System

Tip:

You see bubbles in the sight glass. The air from vents in
the cab is only slightly cool.

Cause:

Insufficient refrigerant (charge) in the system.

Troubleshooting & Service Procedures

Figure 8-5

Gauge reading, low
refrigerant charge in the
system.

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Repair Procedure:

Check for leaks with your leak detector. If you find a leak
at a connection, tighten it then add refrigerant as neces-
sary. If a component or line is leaking (defective), recover
all refrigerant from the system. Replace the defective part
and then check the compressor oil level and replace
missing oil. Evacuate and recharge with refrigerant, then
check AC operation and performance.

Extremely Low Refrigerant Charge in the System

Tip:

The sight glass is clear or shows oil streaks. The air from
vents in the cab seems warm. If there is a low pressure or
Trinary™ switch in the system it may have shut off the
compressor (clutch).

Cause:

Extremely low or no refrigerant in the system. There is a
leak in the system.

Repair Procedure:

Add refrigerant to the system, at least half of the normal
full charge amount. Then perform your leak test. As an
alternative to a refrigerant, add dry nitrogen gas to the
system and then test for leaks.

Note:

It may be necessary to use a jumper wire to bypass some
types of low pressure cutout switches to operate the
compressor (clutch) when you add refrigerant to the
system.

Manifold Gauge Set Readings

Figure 8-6

Gauge reading, extremely
low refrigerant charge in
system.

Takeuchi compact excavator TB125, TB135, TB145 / diesel TNE / diesel Yanmar. Service Manual - page 15