Chapter 8- Troubleshooting & Service Procedures
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-
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.
Low Refrigerant Charge in the System
Gauge reading, low refriger-
ant charge in the system.
You see bubbles in the sight glass. The air from
vents in the cab is only slightly cool.
Insufficient refrigerant (charge) in the system.