GEAR-DRIVE 7G3208 - Caterpillar

Problem: The cooling effect is poor due to abnormal low side pressure.
Check the refrigerant pressure on the low side.Expected Result: The pressure is abnormally high. The pressure measures approximately 290 kPa (42 psi) or more.Results:
OK - Proceed to step 2.
NOT OK - Proceed to step 5 if the pressure is approximately 50 kPa (7.5 psi) or less..
Check the system for an overcharge of refrigerant.Reference: Refer to "Problem: The system is overcharged with refrigerant. This causes poor cooling by the condenser." for further information.Expected Result: The amount of refrigerant charge is correct.Results:
OK - Proceed to step 3.
NOT OK - Recover the refrigerant until the level is correct.. Refer to Testing and Adjusting, "Refrigerant Recovery".
Check the compressor for proper functionallity. The following problems could exist:
bad gasket at the head of the compressor
failed suction valve
debris cought in the suction valveExpected Result: The compressor functions properly.Results:
OK - The opening of the expansion valve is too great. Proceed to step 4.
NOT OK - Replace the compressor.
Check the contact of the thermal tube.Expected Result: The thermal tube is correct.Results:
OK - Replace the expansion valve.
NOT OK - Repair the poor contact of the thermal tube.Note: An abnormally low ambient temperature can cause low pressure.
Check the system for an undercharge of refrigerant.Reference: Refer to "Problem: The system has an insufficient amount of refrigerant charge." for further information.Expected Result: The system is charged correctly.Results:
OK - Proceed to step 6.
NOT OK - Perform a leak test and charge the system to the correct level. Refer to Testing and Adjusting, "Refrigerant Leakage - Test" for the proper procedures. Be sure to repair any leaks that are found before you charge the system.
Check the receiver-dryer for clogging.Expected Result: The receiver-dryer is not clogged.Results:
OK - Proceed to step 7.
NOT OK - Replace the receiver-dryer.
Check for a clogged expansion valve and check for a gas leak at the thermal tube.Expected Result: The expansion valve is functioning properly.Results:
OK - Proceed to step 8. The evaporator is freezing.
NOT OK - Replace the expansion valve. If temporal clogging has caused a frozen expansion valve, moisture is mixed in the refrigerant circuit. If this situation exists, replace the receiver-dryer and the expansion valve. You must evacuate the system and recharge the system after these repairs are made.
Stop operating the air conditioner in order to check the voltage at the magnetic clutch.Expected Result: Voltage is supplied at the magnetic clutch.Results:
OK - Proceed to step 9.
NOT OK - Replace the magnetic clutch.
Check a/c clutch relay (19) .Reference: Refer to Testing and Adjusting, "Air Conditioning System Schematic" for the proper wiring diagram.Expected Result: The relay is functioning properly.Results:
OK - Proceed to step 10.
NOT OK - Replace a/c clutch relay (19) .
Make sure that the evaporator sensor does not have a short circuit.Expected Result: A short circuit does not exist.Results:
OK - Proceed to step 11.
NOT OK - Repair the short circuit.
Illustration 8 g00455508
Heater/Air conditioner unit
Check the resitance of the evaporator sensor (12) .Reference: Refer to Systems Operation, "Air Conditioning and Heating System Sensor Operation" for a graph that shows resistance versus