A/c System Diagnosis - Manual GMC Suburban R1500

INSUFFICIENT COOLING

Note. This procedure may be used to determine whether or not the A/C system has the proper refrigerant charge, providing ambient air temperature is above 70°F (21°C).

QUICK CHECK PROCEDURE

1. Engine must be at normal operating temperature, choke must be open, and throttle must be off fast idle speed cam. Open vehicle's doors and engine hood.
2. Set function lever to "NORM" position, temperature lever at "COLD" position, and blower on "HI" position. Engine should be at normal slow idle speed.
3. Feel the temperature of the accumulator surface and the evaporator inlet pipe while the compressor is engaged. On some vehicles it is normal for the compressor to cycle on and off to meet system requirements.
4. If the accumulator surface and evaporator inlet pipe are both at the same temperature, and slightly cooler than ambient air, system is normal. If inlet pipe is frosted or feels cooler than accumulator surface, refrigerant charge is low.
5. Add refrigerant in 4 oz. increments, allowing system to stabilize between additions, until both feel same temperature. Add 14 oz. more refrigerant.

Note. CCOT system does not have a sight glass. DO NOT install a sight glass.

THOROUGH CHECK PROCEDURE

1. Attach manifold gauge set, and refer to «CCOT SYSTEM INSUFFICIENT COOLING CHARTS»(/gmc/suburban-r1500/1987-1991/remont/manual-hvac-system/#ac-system-diagnosis-manual) and «V5 SYSTEM INSUFFICIENT COOLING CHARTS»(/gmc/suburban-r1500/1987-1991/remont/manual-hvac-system/#ac-system-diagnosis-manual) below. Compressor clutch cycles on and off during normal operation.
2. When using insufficient cooling charts, note that procedures apply to all models. When checking compressor clutch cycling, it may be necessary to jumper different cut-off switches and relays to check system fully.

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OPERATIONAL TESTING

When trouble shooting and diagnosing an air conditioning system, always refer to the appropriate vacuum and wiring diagrams for the system involved. Refer to the applicable operational chart for characteristics, and note the following

1. Blower operation at all 4-speeds and engagement of the compressor clutch would indicate that electrical circuits are functioning properly.
2. If evaporator inlet pipe and accumulator surface both appear to be the same temperature when felt by hand, system is properly charged with refrigerant.
3. An indication of proper vacuum and diaphragm function is selector lever operation.

BLOWER MOTOR WON'T RUN

1. Check fuses. Turn ignition switch to "RUN", and check for voltage at function control switch.
2. Switch blower selector to "HI" position and check for voltage at switch and at high speed blower relay.
3. Ground blower motor with ignition switch in "RUN".

BLOWER DOES NOT OPERATE IN "HI"

1. Check for voltage at high speed blower relay with ignition in "RUN" and blower switch in "HI". If not OK, check for voltage at blower switch.

BLOWER OPERATES ONLY IN "HI"

1. Check blower resistors for open condition.

BLOWER OPERATES IN "HI" WITH IGNITION SWITCH "OFF"

1. Check blower motor relay.

AIR CONDITIONER DOESN'T WORK

1. With engine running and mode lever at "NORM", check for voltage at pressure cycling switch.
2. Check for voltage between pressure cycling switch and compressor clutch.
3. Ground compressor clutch circuit. If clutch engages, check wide-open throttle cut-out switch and A/C compressor cut-off switch.

Note. To check Celebrity with 2.5L or 2.8L engine, Pontiac Sunbird with 2.0L MFI engine, see appropriate ECM article in the COMPUTER ENGINE CONTROL Section.

VACUUM SYSTEM DIAGNOSIS

1. With engine idling, move mode selector lever to each position. If airflow is not as shown in vacuum diagram operational charts (see appropriate vacuum diagram), go to next step.
2. Check for poor vacuum hose connections at actuators, control head valve, reservoir, tees, etc. Check vacuum source circuit by installing tee and gauge (with restrictor) at vacuum outlet.
3. Idle engine, and check that vacuum is equivalent to engine vacuum in all selector positions. If vacuum is less than normal in all positions, remove tee and connect gauge line directly to tank.
4. If vacuum is normal, problem is downstream. If vacuum is less than normal in some positions, problem is in the feed circuit.
5. If vacuum was normal and even at all positions, malfunction may be caused by improperly connected, plugged lines, or a defective vacuum valve(s).
6. To check a specific vacuum circuit, place mode selector lever in the malfunctioning position. Check for vacuum at the affected actuator. If vacuum exists, but door does not move, actuator is defective or binding.
7. If low or no vacuum exists at the actuator, determine whether the vacuum harness or vacuum valve is faulty. Check vacuum harness first.

See also:
• CCOT SYSTEM INSUFFICIENT COOLING CHARTS