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Chapter 8

– Troubleshooting & Service Procedures

8-10

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Index

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 condi-

tions.

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 appro-

priate service and repair procedures.

0

100

200 300

400

500

HIGH

TEMPERATURE

LOW

TEMPERATURE

150

120

90

60

30

0

10

20

30

Low Refrigerant Charge in the System

LOW SIDE LOW

HIGH SIDE LOW

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.

Figure 8-5

Gauge reading, low refriger-

ant charge in the system.