A/c System General Servicing: Other Chevrolet Sportvan G20

SAFETY PRECAUTIONS - USING R-12 REFRIGERANT

1. Always work in a well-ventilated, clean area. Refrigerant (R-12) is heavier than oxygen, and will displace oxygen in a confined area. Always wear eye protection when working around air conditioning systems and R-12. The system's high pressure can cause severe injury to eyes and skin if a hose were to burst. R-12 evaporates quickly when exposed to atmosphere, freezing anything it contacts.
2. Use care when handling refrigerant containers. DO NOT drop or strike containers or expose refrigerant containers to excessive heat. Containers must never be heated more than 125°F (52°C). Never expose R-12 directly to open flame.

SAFETY PRECAUTIONS - USING INDIVIDUAL R-12 CANS

Disposable refrigerant cans (referred to as one pound cans) have a flat type seal or a screw type seal, and proper can tap must be used for each type. Be sure sealing gasket on can tap is in good condition. A proper safety can tap will prevent refrigerant from flowing back into open can, as tap has a one-way flow control.

Note. Recent findings by the EPA indicate that refrigerant is harmful to the Earth's protective Ozone layer. When discharging refrigerant avoid allowing refrigerant to enter the atmosphere. Refrigerant recovery system should be used when discharging the system.

SAFETY PRECAUTIONS - MULTI-CAN DISPENSING VALVES

A multi-can dispensing valve allows attachment of several cans of refrigerant, and is a good substitute when a bulk container is not available. Cans are installed onto each leg of multi-can dispensing valve in the same manner as the individual cans, and each leg has its own can tap.

FLAT TYPE SEAL CANS

On cam-lock or one-piece can taps, first turn the handle outward to the fully open position. Securely engage locking lugs over the can flange, and lock them in place by turning cam lock or locking nut. Screw tap assembly into adapter so sealing gasket is fully seated against the can top. Turn tap inward to pierce the can and close the tap. DO NOT open tap until ready to purge the service hose or dispense refrigerant into the system.

On 2-piece can taps, be certain tap handle is turned fully inward to the closed position. Check that locking base is turned to its outer limit. Securely engage locking lugs over the can flange. Turn entire tap assembly (without disturbing the closed setting) downward into the locking base to pierce the can. DO NOT open tap until ready to dispense into system.

SCREW TYPE SEAL CANS

Ensure can tap is fully closed. Screw refrigerant can into can tap fitting until tight. This will pierce the can. Connect tap to center hose on manifold gauge set. DO NOT open tap until ready to dispense R-12 into system.

SIGHT GLASS INDICATORS

Note. Receiver-drier may be used on some models, while other models use an accumulator.

A sight glass (if used) is usually mounted in receiver-drier or in discharge line to expansion valve. Through sight glass, a visual check of refrigerant condition passing through the system can be made. There are several "indicators" that help diagnose possible problems. (Scheme 8) These "indicators" are outlined as follows

CLEAR SIGHT GLASS

A clear sight glass indicates system has correct charge of refrigerant or is excessively low on refrigerant for system circulation. Sight glass may be clear and system may contain excessive R-12. This must be verified with test gauge readings.

BUBBLY/FOAMY SIGHT GLASS

A "bubbly" or "foamy" sight glass indicates system is low on refrigerant, and air has probably entered system. However, if only occasional bubbles are noticed, during clutch cycling or system start-up, this may be a normal condition.

OIL STREAKED SIGHT GLASS

If oil streaks appear on sight glass, a lack of refrigerant may be indicated, and the system's compressor oil is circulating through the system.

CLOUDY SIGHT GLASS

A cloudy sight glass indicates desiccant contained in receiver-drier or accumulator has broken down and is being circulated through system. Sight glass readings are not necessarily positive identification of a problem. Readings should be relied upon only in conjunction with other system symptoms.

Scheme 8

BACK-SEATED (OPERATING) POSITION

This is normal operating position, and position used for connecting and disconnecting manifold gauge set. Stem is turned fully outward to seal the service gauge port.

FRONT-SEATED (OFF) POSITION

With service valve stem turned inward, valve blocks refrigerant flow through system, isolating compressor for service.

Scheme 9

SPECIAL VALVE CONNECTORS

Most General Motors vehicles use a high side service valve with a different thread size than that on low side (3/8-24 thread on high side and 7/16-20 on low side). Special adapters are required to make this connection. These adapters are available in 45 degree and 90 degree angles, in addition to straight fixed and flexible adapters.

MANIFOLD GAUGE SET

A manifold gauge set is used to determine system's high and low side pressures, correct refrigerant charge, system diagnosis and operating efficiency. High (discharge) and low (suction) pressures must be compared to determine system operation.

LOW SIDE GAUGE

This gauge, which may have a Blue color identifying feature, is used to measure low side (suction) pressure. It reads from 0 to 150 psi (pressure scale) and from 0 to 30 inches of mercury (vacuum scale). This low side gauge is called a compound gauge because it has a dual purpose, to register either pressure or vacuum.

HIGH SIDE GAUGE

The high side gauge, which may have a Red identifying feature, is used to measure high side (discharge) pressure. It reads from 0 to 500 psi.

SCHRADER-TYPE VALVES

1. Put on safety goggles and cover vehicle's fender. Remove protective caps from Schrader valves. Do this slowly to check for leaky valves. CAUTION: Be sure hand valves on manifold gauge set are closed before connecting test hoses to Schrader valves.
2. Be sure service hoses are equipped with valve core depressor to match Schrader valve. If not, install special adapters for this purpose. Ensure both manifold gauge hand valves are closed.
3. Connect low side service hose to low side (suction) service valve. Tighten finger tight. Connect high side service hose to high side (discharge) service valve. Tighten finger tight.

STEM-TYPE VALVES

1. Put on safety goggles and cover vehicle's fender. Place valves in back-seated position. Remove protective caps from service valves. Do this slowly to check for leaky valves. CAUTION: Be sure hand valves on manifold gauge set are closed before turning service valve to the mid-position.
2. Attach low side service hose to the low side (suction) service valve. Connect high side service hose to the high side (discharge) service valve. Tighten both connectors finger tight.

Note. After test gauges are installed, you must purge test hoses of all air before proceeding with testing.

STABILIZING A/C SYSTEM

1. Once manifold gauge set is attached to system, and test hoses have been purged, system is ready for testing. Place all test hoses, gauge set and other equipment away from all engine moving parts.
2. Start engine and turn air conditioner controls to maximum cooling (full cold and "MAX A/C"). Set blower fan on high speed. Open doors and/or windows and operate system for 5-10 minutes. System should now be stabilized and ready for test readings.

PRESSURE GAUGE READINGS

The following typical pressure gauge indications represent conditions that may be encountered during system servicing. Temperature and humidity, as well as other factors, affect pressure gauge readings. Pressure gauge indications should be used only as a guide.

EXCESSIVE MOISTURE GAUGE READINGS

Low Side Gauge - Normal-to-Low

High Side Gauge - Normal

CORRECTION

1. Discharge refrigerant from system using approved refrigerant recovery/recycling equipment.
2. Replace receiver-drier, accumulator or desiccant bag.
3. Evacuate system with vacuum pump.
4. Charge system with R-12.
5. Operate system and check performance.

DEFECTIVE THERMOSTATIC SWITCH GAUGE READINGS

Low Side Gauge - Normal

High Side Gauge - Normal

1. Stop vehicle engine and turn air conditioner "OFF".
2. Remove and discard old clutch cycling switch, install a new switch of same type.
3. Operate system and check performance.

MISADJUSTED THERMOSTATIC SWITCH GAUGE READINGS

See DEFECTIVE CLUTCH CYCLING SWITCH PRESSURE GAUGE READINGS below.

DEFECTIVE CLUTCH CYCLING SWITCH PRESSURE GAUGE READINGS

Low Side Gauge - Low-to-Normal/Normal-to-High

High Side Gauge - Normal

Compressor

Cycles at incorrect temperature or pressure.

Evaporator

May freeze and restrict airflow if switch is allowing compressor to remain on too long.

Scheme 10

CORRECTION WITH THERMOSTATIC SWITCH

Note. If no adjusting screw is provided, the switch is nonadjustable and must be replaced.

1. Stop engine and turn air conditioner off.
2. Remove components necessary to gain access to thermostatic adjustment screw.
3. Make certain that all wiring is positioned so that no short-circuiting can occur. Connect battery cable so that engine can be operated while making switch adjustment. Adjust thermostatic switch.

Note. A pressure sensing switch is used on most late General Motors models with accumulator-type systems. It performs the same function as thermostatic switch.

CORRECTION WITH CLUTCH CYCLING SWITCH

Note. Switch is non adjustable and is mounted on a Schrader valve fitting. Therefore, no system discharge is required.

1. Stop engine and turn air conditioner off.
2. Detach electrical connector from pressure sensing switch at accumulator.
3. Remove pressure sensing switch, and install a new switch.

LOW R-12 CHARGE GAUGE READINGS

Low Side Gauge - Low

High Side Gauge - Low

1. Leak test system.
2. Discharge refrigerant from system, using approved refrigerant recovery/recycling equipment, if necessary to replace units or lines.
3. Repair leaks.
4. Check compressor oil level. System may have lost oil due to leakage.
5. Evacuate system using vacuum pump.
6. Charge system with R-12.
7. Operate system and check performance.

VERY LOW R-12 CHARGE GAUGE READINGS

Low Side Gauge - Low

High Side Gauge - Low

Operation may have stopped if system is equipped with a refrigerant pressure sensing switch.

Scheme 11

1. If compressor operation is stopped due to a pressure sensing switch, by-pass switch with jumper wire until testing and correction are complete.
2. Add a partial refrigerant charge (to at least 50 percent system capacity), then make thorough leak test.
3. Discharge refrigerant from system using approved refrigerant recovery/recycling equipment.
4. Check compressor oil level. System may have lost oil due to leakage.
5. Evacuate system using vacuum pump.
6. Charge system with R-12.
7. Operate system and check performance.

ORIFICE TUBE PLUGGED GAUGE READINGS

Low Side Gauge - Low

High Side Gauge - Low

1. Evacuate system using vacuum pump.
2. Replace orifice tube.
3. Charge system with R-12.
4. Operate system and check performance.

EXPANSION OR "H" VALVE STUCK CLOSED

Low Side Gauge - Low

High Side Gauge - Low

1. Evacuate system using vacuum pump.
2. Charge system with R-12.
3. Operate system and check performance.

EXPANSION OR "H" VALVE STUCK OPEN GAUGE READINGS

Low Side Gauge - High

High Side Gauge - High

1. If expansion valve test indicates valve operation is satisfactory, proceed as follows: Clean contact surface of evaporator outlet pipe and temperature sensing bulb, then clamp bulb securely in contact with pipe and recover with proper insulation tape. Operate system and check performance.
2. If expansion valve test indicates valve is defective, proceed as follows: Discharge system using approved refrigerant recovery/recycling equipment. Replace expansion valve, making sure all contacts are clean and secure. Evacuate system using vacuum pump, then charge system with R-12. Operate system and check performance.

COMPRESSOR MALFUNCTION GAUGE READINGS

Low Side Gauge - High.

High Side Gauge - Low.

1. Isolate compressor (if equipped with stem-type service valves) or discharge entire system using approved refrigerant recovery/recycling equipment.
2. Remove compressor cylinder head and inspect compressor. Replace reed valve plate assembly if necessary. Install cylinder head using NEW gasket.
3. Check compressor oil level.
4. Replace receiver-drier, desiccant or accumulator if: System previously opened. System operated two or more seasons with present unit. Compressor inspection revealed desiccant particles (very fine golden or brown particles).
5. Using vacuum pump, evacuate compressor or entire system (depending on procedure used in step 1).
6. Charge system with R-12.
7. Operate system and check performance.

CONDENSER MALFUNCTION OR R-12 OVERCHARGE GAUGE READINGS

Low Side Gauge - High

High Side Gauge - High

1. Check electric cooling fan operation.
2. Inspect condenser for clogged air passages, bug screen, or other obstructions preventing airflow through condenser.
3. Inspect condenser mounting for proper radiator clearance. Inspect clutch type fan for proper operation. Inspect radiator pressure cap for correct type and proper operation. NOTE: After Making Above Corrections. Operate system and check performance. If Condition is Not Corrected perform the following
4. Inspect system for overcharge of refrigerant and correct as follows: Discharge refrigerant, using approved refrigerant recovery/recycling equipment, until stream of bubbles appears in sight glass and both high and low gauge readings drop below normal. Add R-12 until bubbles disappear and pressures are normal, then add an additional 1/4-1/2 lb. of refrigerant.
5. Operate system and check performance. If gauge readings are Still Too High: Discharge system using approved refrigerant recovery/recycling equipment, and remove and inspect condenser to ensure free passage of refrigerant or replace condenser. Replace receiver-drier, desiccant bag or accumulator. Evacuate system using vacuum pump. Charge system with R-12. Operate system and check performance.

ORIFICE TUBE LOCATION & REMOVER/INSTALLER ID (PASSENGER CARS) (1)

ORIFICE TUBE LOCATION & REMOVER/INSTALLER ID (TRUCKS & VANS) (1)

1. If difficulty is encountered during removal of a plugged or restricted orifice tube, remove as much impacted residue as possible.
2. Using a heat gun, carefully apply heat on inlet pipe. If inlet pipe contains small dimples in the line, apply heat 1/4" away from the dimples. On all applications, use care not to overheat pipe. NOTE: If system has a pressure switch near orifice tube location, remove pressure switch prior to heating the pipe to avoid switch damage.
3. While heat is being applied, install proper orifice tube remover/installer in orifice tube. Use a turning motion along with a push or pull motion to loosen orifice tube and remove it.

REFRIGERANT RECOVERY

1. Close both valves on manifold gauge set. Connect manifold gauge set to high and low side service valves.
2. Connect center hose on manifold gauge set to inlet port on Refrigerant Recovery/Recycle System (J-38100-B). Start engine. Turn A/C on for approximately 2 minutes. NOTE: Operating A/C for 2 minutes will warm the refrigerant so refrigerant recovery/recycle system can recover more refrigerant from the system.
3. Shut engine off. Open BOTH valves on manifold gauge set. Open BOTH valves on refrigerant recovery/recycle system storage tank at the same time.
4. Plug refrigerant recovery/recycle system in and turn power switch on. Depress compressor START switch and note that the compressor ON light is activated.
5. The refrigerant recovery/recycle system will shut off when a vacuum reading of 17 in. Hg is obtained on manifold gauge set. Manifold gauge vacuum reading should remain at 17 in. Hg for at least 2 minutes.
6. If reading increases to above zero, refrigerant still remains in the vehicle A/C system. Depress compressor START switch and operate refrigerant recovery/recycle system through another cycle.
7. Once refrigerant is recovered, open accumulator pressure valve on the refrigerant recovery/recycle system for 15 seconds. This will pressurize the oil separator so refrigerant oil can be drained.
8. Open OIL DRAIN valve on the refrigerant recovery/recycle system and drain refrigerant oil into a container. Measure exact amount of oil to be added when system is put back in service.

DISCHARGING A/C SYSTEM

Note. Recent findings by the EPA indicate that refrigerant is harmful to the Earth's protective Ozone layer. When discharging refrigerant, avoid allowing refrigerant to enter the atmosphere. Refrigerant recovery/recycle system should be used whenever possible instead of discharging system. Many states now require by law the use of recovery/recycle systems. Check local laws before proceeding.

General Motors does not provide procedures for discharging of A/C system. To discharge system, follow procedures for refrigerant recovery using a recovery/recycle system as outlined under REFRIGERANT RECOVERY .

CHARGING A/C SYSTEM

Note. DO NOT connect high side gauge hose to high side service port. Perform A/C charging service through low side only.

1. System must be evacuated before charging. With manifold gauge set attached from evacuation procedure, start engine, but DO NOT turn on A/C. With gauges and R-12 drum (inverted for liquid charging) connected from evacuation procedure, open low side gauge valve on manifold gauge set. Allow one pound of R-12 to enter system.
2. When one pound of R-12 has entered system, turn A/C to NORM position with blower on high speed. Continue charging (liquid charging) until proper amount of R-12 has entered system.
3. Close R-12 drum valve and continue running A/C system for 30 seconds to clear lines and gauges. Turn off valve on manifold gauge set. With engine running, disconnect low side hose and install service valve cap at accumulator. Perform leak test procedure.