A/c System General Servicing GMC Jimmy Typhoon

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 1) 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.

Sight Glass Indicators. Scheme 1

1992 PASSENGER CAR SERVICE VALVE LOCATIONS

1992 TRUCK/VAN SERVICE VALVES LOCATION

1992 TRUCKS & VANS SERVICE VALVE LOCATIONS

STEM-TYPE VALVE OPERATION

This manually operated service valve has adjustable stem, located under a protective cap. Valve stem must be manually positioned when making gauge connections and/or reading system pressure on the gauges. (Scheme 2)

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.

MID (TEST) POSITION

After service gauge manifold set has been installed (valve stem in back-seated position), turn valve stem 1 1/2 to 2 turns inward. This positions valve stem midway, allowing full system operation and permits refrigerant pressure to reach gauges.

FRONT-SEATED (OFF) POSITION

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

Stem-Type Service Valve Positions. Scheme 2

SCHRADER-TYPE VALVE OPERATION

Schrader valve is similar in construction and operation to a tire valve. When a test gauge hose (which has a valve core depressor) is attached, Schrader stem is pushed inward to the open position and allows system pressure to reach the gauge.

If test hose being used does not have a built-in core depressor, an adapter must be used. Never attach hoses or adapters to a Schrader valve unless it is first connected to manifold gauge set.

Note. Although similar in construction and operation to a tire valve, the Schrader-type valve cannot be replaced with a tire valve.

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.

PURGING TEST HOSES

1. Be sure high and low side hoses are properly connected to service valves and all hose connections are tight.
2. If stem-type service valves are used, turn stems inward 1 1/2 to 2 turns to mid-position. Place clean shop towel over end of center service hose.
3. Now purge high side test hose by opening hand valve on the high side gauge for 3-5 seconds. This allows system's refrigerant to force air through test hoses and out center service hose into the shop towel. Immediately close high side gauge hand valve.
4. Purge low side test hose in the same manner, using hand valve of low side gauge. Close hand valve after 3-5 seconds. Purging of test hoses is complete. System is ready for 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

OTHER SYMPTOMS

Sight Glass - Tiny bubbles.

Discharge Air - Becomes warm as low side cycles into vacuum. As moisture is released by saturated desiccant, it becomes released by saturated desiccant, it becomes trapped and freezes at expansion valve or orifice tube, blocking R-12 flow into the evaporator. As low side drops to a vacuum, high side may rise.

Excessive Moisture Pressure Gauge Indications. Scheme 3

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

Compressor - Cycles on and off too fast.

Low Side Gauge - Not enough range shown on low side gauge.

Defective Thermostatic Switch Pressure Gauge Indications. Scheme 4

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.

Misadjusted Thermostatic Switch or Defective Clutch Cycling Switch Gauge Indications. Scheme 5

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

Discharge Air - Slightly cool.

Sight Glass - Some bubbles.

Low R-12 Charge Pressure Gauge Indications. Scheme 6

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

Discharge Air - Warm.

Sight Glass - Clear or Oil Streaks.

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

Very Low R-12 Charge Pressure Gauge Indications. Scheme 7

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

Discharge Air - Slightly cool.

Evaporator Inlet Pipe - Sweating or frost build up just ahead of orifice tube.

TESTING

If evaporator inlet pipe after orifice tube and accumulator surface are warm, orifice tube is plugged.

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

Discharge Air - Slightly cool.

Evaporator Inlet Pipe - Sweating or frost build up.

1. If evaporator inlet is cool to touch, proceed as follows: Set air conditioner for maximum cooling and operate the system. Spray liquid R-12 on head of valve or capillary tube if equipped). Note low side gauge reading. Low side gauge should drop into a vacuum. If low side vacuum reading was obtained, warm expansion valve diaphragm chamber with hand, then repeat test step b.). If expansion valve test indicates valve operation is satisfactory, clean contact surface of evaporator outlet pipe and temperature sensing bulb. Make sure bulb is securely in contact with pipe. If expansion valve test indicates the valve is defective, discharge the system, using approved refrigerant recovery/recycling equipment. Replace expansion valve, and proceed with correction procedure.
2. If expansion valve inlet shows sweating or frost proceed as follows: Discharge system using approved refrigerant recovery/recycling equipment. Disconnect inlet line at expansion valve. Remove and inspect screen. Clean and replace screen and reconnect inlet line. Proceed with correction procedure.

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

Discharge Air - Warm

Evaporator - Sweating or frost.

Check for expansion valve stuck open, or incorrect mounting of temperature sensing bulb as follows

1. Set air conditioner for maximum cooling and operate system several minutes.
2. Spray liquid R-12 on head of valve or capillary bulb, and note low side gauge reading. It should drop into a vacuum (if not, a stuck open valve or incorrect bulb mounting is indicated). This test may not be possible on applications where sensing bulb is not accessible.
3. If low side vacuum reading is obtained, warm expansion valve diaphragm chamber with hand, then repeat test.

Expansion or "H" Valve Stuck Open Pressure Gauge Indications. Scheme 8

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

Compressor - Noisy.

Compressor Malfunction Pressure Gauge Indications. Scheme 9

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

Discharge Air - Warm.

High Side Lines - Very Hot.

Sight Glass - Bubbles.

Condenser Malfunction or R-12 Overcharge Pressure Gauge Indications. Scheme 10

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.

After Making Above Corrections. Operate system and check performance. If Condition is Not Corrected.

1. 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.
2. Operate system and check performance. If Gauge Readings Still Too High Discharge system, using approved refrigerant recovery/recycling equipment. 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.

REMOVAL

1. Orifice tube may be located at condenser outlet or evaporator. See 1992 ORIFICE TUBE LOCATION & REMOVER/INSTALLER APPLICATION table below. Discharge refrigerant from system using approved refrigerant recovery/recycling equipment and disconnect liquid line at evaporator or condenser.
2. Remove orifice tube using needle nose pliers or proper orifice tube remover/installer. See 1992 ORIFICE TUBE LOCATION & REMOVER/INSTALLER APPLICATION table below.

1992 ORIFICE TUBE LOCATION & REMOVER/INSTALLER APPLICATION

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.

INSTALLATION

1. To install orifice tube, coat pipe area with refrigerant. Lubricate new orifice tube and "O" ring with refrigeration oil and insert into inlet pipe.
2. Install orifice tube with shorter screen end first. To complete installation, reverse removal procedure. Evacuate and recharge system. Test system for proper operation.

REFRIGERANT RECOVERY

1. Close both valves on manifold gauge set. Connect manifold gauge set to high and low side service valves. See SERVICE VALVE LOCATIONS in this article.
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 in this article.

FLUSHING A/C SYSTEM

1. Manufacturer does not recommend flushing A/C system. If system is contaminated, discharge system using approved refrigerant recovery/recycling equipment and install a liquid line filter between condenser and evaporator.
2. Filter may be an integral part of the line or line may need to be cut and filter installed (non-integral type). Filters may contain an orifice. (Scheme 11)
3. Filters with orifice are used when filter is being installed on low pressure side of the orifice tube. Original orifice tube must be removed if filter with orifice is installed. Filter without the orifice must be installed on the high pressure side of the orifice tube.
4. To install liquid line filter, discharge A/C system using approved refrigerant recovery/recycling equipment and remove liquid line. Using a tubing cutter, cut section from liquid line to allow installation of liquid line filter. Clean all burrs and smooth surfaces.
5. Install nut over the line. Install ferrule on line with small end toward the nut. DO NOT install "O" ring at this time.
6. Push line into fitting until it bottoms on filter assembly. Tighten nuts on each joint to 11 ft. lbs. (15 N.m). Disassemble joint assembly.
7. Install new "O" rings, lubricated with refrigeration oil, on the lines. Install filter assembly. Ensure arrow on filter indicates proper flow of refrigerant. Tighten nuts to 11 ft. lbs. (15 N.m). Evacuate system and charge system. Check for leaks.

Scheme 11

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.