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TRUCK SERVICE MANUAL
TM 5-4210-230-14&P-1
BODIES AND CABS
TROUBLE SHOOTING GUIDE
Outlined below are possible causes of problems most frequently experienced with the heating/air conditioning system.
When analyzing air conditioning operational problems, it is required that the manifold gauge set be connected to the
compressor service ports and that the system be operated for a sufficient period to normalize (e g. to have removed the initial heat
from the cab and settled to an average flow rate and pressure). See Performance Checks under SERVICE OPERATIONS.
Problem
Possible Cause
No Heat.
1. Kinked or obstructed heater hoses.
2. Faulty blower motor, resistor assembly or switch.
3. Plugged or defective heater core.
4. Faulty water flow control valve.
5. Faulty control assembly or cables.
Insufficient Heat.
1. Kinked or obstructed heater hoses.
2. Faulty blower motor, resistor assembly or switch.
3. Faulty water flow control valve.
4. Obstructed heater core.
5. Faulty control assembly or cables.
6. Poor sealing around vent door, blend door or other cab
areas.
Too Much Heat (Heater
won't regulate).
1. Blend door cable disengaged or misadjusted.
2. Faulty water control valve.
All Air Flow Coming from
1. Faulty control assembly.
Defroster Outlets.
2. Control cable defective or disengaged from defrost door.
No Cooling.
1. Loss of Refrigerant.
2. Broken or slipping compressor drive belt.
3. Inoperative Compressor Clutch.
4. Frozen or faulty expansion valve.
5. Faulty thermostat control.
6. Faulty compressor.
7. Broken refrigerant line.
Insufficient Cooling.
1. Low refrigerant charge.
2. Clogged air filter.
3. Obstructed air passages.
4. Slipping compressor drive belt.
5. Inoperative or faulty blower or switch.
6. Faulty thermostatic control switch.
7. Faulty expansion valve.
8. Faulty compressor.
CTS-2731 Page 42
PRINTED IN UNITED STATES OF AMERICA
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