A/c System General Servicing Chevrolet Cab & Chassis K3500

HANDLING/SAFETY PRECAUTIONS

1. Always work in a well-ventilated, clean area. Refrigerant (R-12 or R-134a) is colorless and invisible as a gas. Refrigerant is heavier than oxygen and will displace oxygen in a confined area. Avoid breathing refrigerant vapors. Exposure may irritate eyes, nose and throat.
2. The system's high pressure can cause severe injury to eyes and skin if a hose were to burst. Always wear eye protection when working around A/C system and refrigerant. If necessary, wear rubber gloves or other protective clothing.
3. Refrigerant evaporates quickly when exposed to atmosphere, freezing anything it contacts. If liquid refrigerant contacts eyes or skin (frostbite), DO NOT rub eyes or skin. Immediately flush affected area with cool water for 15 minutes and consult a doctor or hospital.
4. Never use R-134a in combination with compressed air for leak testing. Pressurized R-134a in the presence of oxygen (air concentrations greater than 60 percent by volume) may form a combustible mixture. DO NOT introduce compressed air into R-134a containers (full or empty), A/C system components, or service equipment.
5. DO NOT expose A/C system components to high temperatures (steam cleaning for example), as excessive heat will cause refrigerant system pressure to increase. Never expose refrigerant directly to open flame. If refrigerant needs to be warmed, place bottom of refrigerant tank in warm water. Water temperature MUST NOT exceed 125°F (52°C).
6. Use care when handling refrigerant containers. DO NOT drop, strike, puncture, or incinerate containers. Use Department Of Transportation (DOT) approved (DOT 4BW or DOT 4BA) refrigerant containers.
7. Never overfill refrigerant containers. The safe filling level of a refrigerant container MUST NOT exceed 60% of the container's gross weight rating. Store refrigerant containers at temperatures less than 125°F (52°C).
8. Freon (R-12) will be sold and stored in White colored containers, while R-134a refrigerant will be sold and stored in 30- or 50-pound Light Blue containers.
9. Refrigerant R-12 and R-134a must never be mixed, as they and their desiccants and lubricants are not compatible. If the refrigerants are mixed, system cross-contamination or A/C system component failure may occur. Always use separate servicing and refrigerant recovery/recycling equipment.
10. Read and follow equipment manufacturer's instructions for all service equipment to be used. The Material Safety Data Sheet (MSDS), provided by refrigerant manufacturer/supplier, contains valuable information regarding the safe handling of refrigerants.

IDENTIFYING R-134a SYSTEMS & COMPONENTS

To prevent refrigerant cross-contamination, use following methods to identify R-134a based systems and components.

Fittings & "O" Rings

All R-134a based A/C systems use 1/2" - 16 ACME threaded fittings (identifiable by square threads) and quick-connect service couplings. (Scheme 6)

Scheme 6

Underhood A/C Specification Labels

Most R-134a based systems will be identified through the use of underhood labels with R-134a refrigerant clearly printed on labels. (Scheme 7) Most manufacturers will identify refrigerant type with labels affixed to compressor. Before servicing an A/C system, always determine which refrigerant is being used.

Scheme 7

Other Means Of Identification

Refrigerant R-134a is "milky" in appearance due to the mixture of refrigerant and lubricating oil. As the refrigerant and oil DO NOT exhibit a "clear" sight glass on a properly charged A/C system, most R-134a systems have no sight glass.

REFRIGERANT OILS

Refrigerant R-12 based systems use mineral oil, while R-134a systems use synthetic/Polyalkylene Glycol (PAG) oils. Using a mineral oil based lubricant with R-134a will result in A/C compressor failure due to lack of proper lubrication.

Note. Use only specified oil for the appropriate system and A/C compressor. Always check the underhood A/C specification label or A/C compressor label before adding refrigerant oil to A/C compressor/system. (Scheme 7)

The following R-134a refrigerant oils are currently available.

GM

Use PAG Refrigerant Oil (Part No. 12345923).

Note. Synthetic/PAG oils absorb moisture very rapidly, 2.3-5.6% by weight, as compared to a mineral oil absorption rate of .005% by weight.

SERVICE EQUIPMENT

Note. Ensure "O" rings are designed for use with specified refrigerant. Deterioration of "O" rings and system contamination will result if incorrect "O" rings are used.

Because R-134a is not interchangeable with R-12, separate sets of hoses, gauges and recovery/recycling equipment are required to service vehicles. This is necessary to avoid cross-contamination and damaging system.

All equipment used to service systems using R-134a must meet SAE standard. The service hoses on the manifold gauge set must have manual (turn wheel) or automatic back-flow valves at the service port connector ends. This will prevent refrigerant from being released into the atmosphere.

For identification purposes, R-134a service hoses must have a Black stripe along their length and be clearly labeled SAE J2196/134a. The low pressure test hose is Blue with a Black stripe. The high pressure test hose is Red with a Black stripe. The center test hose is Yellow with a Black stripe.

Note. Refrigerant R-12 service hoses will ONLY be labeled SAE J2196.

R-134a manifold gauge sets can be identified by one or all of the following

1. Labeled FOR USE WITH R-134a on set
2. Labeled HFC-134 or R-134a on gauge face
3. Light Blue color on gauge face

In addition, pressure/temperature scales on R-134a gauge sets are different from R-12 manifold gauge sets.

SIGHT GLASS INDICATOR

Note. Sight glass indicator conditions listed are for R-12 systems. Information for R-134a systems is not available from manufacturer.

Not all systems use a sight glass. If used, a sight glass may be mounted in receiver-drier (accumulator) or in discharge line. Refrigerant's condition can be visually checked while passing through sight glass. The following are possible conditions of sight glass indicator, which may help in the diagnosis of problems. (Scheme 8)

Note. Sight glass readings are not positive identification of a problem. Readings should be relied upon only when other system symptoms exist.

Clear Sight Glass

A clear sight glass indicates refrigerant level is correct or is excessively low for system circulation. Sight glass may be clear, but system may contain excessive refrigerant. This must be verified by 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. 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.

Identifying Sight Glass Indicator Conditions. Scheme 8

STEM-TYPE VALVES

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 9)

Identifying Stem-Type Service Valve Positions. Scheme 9

Back-Seated (Operating) Position

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

Mid (Test) Position

After installing manifold gauge set (valve stem in back-seated position), turn valve stem 1 1/2 - 2 turns inward. This positions valve stem midway, allowing full system operation and permitting 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.

SCHRADER-TYPE VALVES

Note. Although similar in construction and operation to a tire valve, NEVER replace a Schrader-type valve with a tire valve.

Schrader valve is similar in construction and operation to a tire valve. When a test gauge hose is attached (hose has built-in valve core depressor), 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.

SERVICE VALVE LOCATIONS

For service valve locations, see SERVICE VALVE LOCATIONS (CARS) or SERVICE VALVE LOCATIONS (TRUCKS & VANS) table.

SERVICE VALVE LOCATIONS

SERVICE VALVE LOCATIONS

SPECIAL VALVE CONNECTORS

All vehicles with R-134a refrigerant use quick-disconnect service valves. To help prevent installing hoses and other parts used on R-12 systems, all fittings on R-134a systems use 1/2"-16 ACME threads.

On some General Motors models, thread size on high-side service valve (3/8-24 threads) is different from thread size on low-side service valve (7/16-20 threads). 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-side 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. Manifold gauge sets for the 2 refrigerant types are basically the same except for fittings at ends of hoses. Fittings are different to ensure connection only to appropriate refrigerant system.

Low-Side Gauge

Low-side gauge, which may have a Blue identifying feature, is used to measure low-side (suction) pressure. Low-side gauge is also called a compound gauge because it can measure pressure and vacuum. Pressure scale ranges from 0 to 150 psi; vacuum scale ranges from 0 to 30 in. Hg.

High-Side Gauge

High-side gauge, which may have a Red identifying feature, is used to measure high-side (discharge) pressure. Gauge scale ranges from 0 to 500 psi.

1. Put on safety goggles, and cover vehicle's fender. Slowly remove protective caps from Schrader valves to check for leaky valves. CAUTION: Ensure hand valves on manifold gauge set are closed before connecting test hoses to Schrader valves.
2. Ensure service hoses are equipped with valve core depressor to match Schrader valve. Special adapters are required if service hoses do not have built-in core depressor. Ensure both manifold gauge hand valves are closed.
3. Connect low-side service hose to low-side (suction) service valve, and finger tighten connections. Connect high-side service hose to high-side (discharge) service valve, and finger tighten connections.

1. Put on safety goggles, and cover vehicle's fender. Place valves in back-seated position. Slowly remove protective caps from service valves to check for leaky valves. CAUTION: Ensure hand valves on manifold gauge set are closed before turning service valve to mid-position.
2. Attach low-side service hose to low-side (suction) service valve. Connect high-side service hose to high-side (discharge) service valve. Finger-tighten both connections.

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

PURGING TEST HOSES

1. Ensure high-side 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 - 2 turns to mid-position. On all applications, place clean shop towel over end of center service hose.
3. Purge high-side test hose by opening hand valve on high-side gauge for 3-5 seconds. This allows system's refrigerant to force air through test hoses and out of 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 now complete, and system is ready for testing.

STABILIZING A/C SYSTEM

1. Once manifold gauge set is attached to system and test hoses have been purged (if required), system is ready for testing. Place all test hoses, gauge set and other equipment away from all moving parts of engine.
2. Start engine, and turn A/C controls to maximum cooling position. 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 INDICATIONS

Note. Pressure gauge indications are for R-12 systems only. For additional information see the A/C COMPRESSOR SERVICING or A/C COMPRESSOR REFRIGERANT OIL CHECKING articles in the AIR CONDITIONING & HEAT section.

The following typical pressure gauge indications represent conditions that may be encountered during R-12 system servicing. (Scheme 10)- (Scheme 19). Temperature and humidity, as well as other factors, affect pressure gauge readings. Compared to R-12 systems, pressure readings on R-134a systems are generally lower for low side pressure and higher for high side pressure. Pressure gauge indications should be used only as a guide.

Scheme 10

Scheme 11

Scheme 12

Scheme 13

Scheme 14

Scheme 15

Scheme 16

Scheme 17

Scheme 18

Scheme 19

ORIFICE TUBE REPLACEMENT

Note. Orifice tube is located in end of liquid line closest to component listed in ORIFICE TUBE LOCATION & REMOVER/INSTALLER APPLICATION table.

Note. If refrigerant system was contaminated, a liquid line filter (with or without an orifice tube) may be installed. See FLUSHING A/C SYSTEM. It is possible for original orifice tube to still be installed in system.

Removal

1. Locate orifice tube. See ORIFICE TUBE LOCATION & REMOVER/INSTALLER APPLICATION table. Discharge A/C system using approved recovery/recycling equipment. Disconnect liquid line at evaporator inlet. Remove orifice, and disconnect liquid line at evaporator or condenser.
2. Remove orifice tube using needle-nose pliers or orifice tube remover. See ORIFICE TUBE LOCATION & REMOVER/INSTALLER APPLICATION table.
3. If difficulty is encountered during removal of a plugged or restricted orifice tube, remove as much residue as possible. Using a heat gun, carefully heat inlet pipe. If inlet pipe has small dimples, apply heat1/4" from dimples. Be careful not to overheat pipe. NOTE: If system has a pressure switch near orifice tube location, remove switch before heating inlet pipe to avoid damaging switch.
4. While heat is being applied, install orifice tube extractor. Use a turning motion along with a push or pull motion to loosen and remove orifice tube.

ORIFICE TUBE LOCATION & REMOVER/INSTALLER APPLICATION

Installation

1. To install orifice tube, coat inside of inlet pipe with refrigerant oil. Lubricate new orifice tube and "O" ring with refrigerant oil and insert them into inlet pipe.
2. Install orifice tube with shorter screen end first. To complete installation, reverse removal procedure. Recharge and test system for proper operation.

REFRIGERANT RECOVERY/RECYCLING

Note. The use of recovery/recycling equipment is required by law.

Refrigerant recovery/recycling equipment is used to remove refrigerant from vehicle's A/C system without polluting atmosphere. To remove and recycle refrigerant, ALWAYS follow instructions provided with the refrigerant recovery/recycling equipment being used.

The removed refrigerant is filtered, dried and stored in a tank within the recovery/recycling equipment until it is ready to be pumped back into the vehicle's A/C system.

Note. Separate sets of hoses, gauges and refrigerant recovery/recycling equipment MUST be used for R-12 and R-134a systems. DO NOT mix R-12 and R-134a refrigerants, as their refrigerant oils and desiccants are NOT compatible.

1. Close both valves on manifold gauge set. Connect manifold gauge set to high-side and low-side service valves. See SERVICE VALVE LOCATIONS under SYSTEM SERVICE VALVES.
2. Connect center hose on manifold gauge set to inlet port on Refrigerant Recovery/Recycling Equipment (J-39500). Start engine. Turn A/C on for about 2 minutes. NOTE: Operating A/C for 2 minutes warms refrigerant, allowing greater recovery of refrigerant from system.
3. Shut engine off. Open both valves on manifold gauge set. Simultaneously open both valves on refrigerant recovery/recycling equipment storage tank.
4. Turn refrigerant recovery/recycling equipment on. Depress compressor START switch. Ensure the compressor ON light is activated.
5. The refrigerant recovery/recycling equipment will shut off when manifold gauge indicates vacuum reading of 17 in. Hg. Vacuum should remain at 17 in. Hg for at least 2 minutes.
6. Run recovery/recycling equipment one complete cycle. If vacuum reading is greater than zero after one complete cycle, some refrigerant still remains in vehicle's A/C system. Depress compressor START switch, and operate refrigerant recovery/recycling equipment through another cycle.
7. Once refrigerant is recovered, open accumulator pressure valve on the refrigerant recovery/recycling equipment for 15 seconds. This will pressurize the oil separator so refrigerant oil can be drained.
8. Open oil drain valve on refrigerant recovery/recycling equipment, and drain refrigerant oil into a container. Measure exact amount of oil to be added when system is put back in service.

FLUSHING A/C SYSTEM

1. Manufacturer does not recommend flushing A/C system. If system is contaminated, discharge system 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 or may not contain orifice. (Scheme 20)
3. Filter with orifice is installed on low pressure side of orifice tube. Remove original orifice tube if installing filter with orifice. Filter without orifice must be installed on high pressure side of orifice tube.
4. To install liquid line filter, discharge A/C system using approved recovery/recycling equipment. 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 line. Install ferrule on line with small end toward 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. Lubricate new "O" rings with refrigerant oil and install them on lines. Install filter assembly. Ensure arrow on filter indicates proper flow of refrigerant. Tighten nuts to 11 ft. lbs. (15 N.m). Evacuate and charge system. Check system for leaks.

Scheme 20

R-12

1. Close both valves on manifold gauge set. Connect low-side gauge hose to low-side service valve. See SERVICE VALVE LOCATIONS under SYSTEM SERVICE VALVES. Connect high-side gauge hose to evacuation pump and center hose to R-12 drum. Ensure valve on R-12 drum is closed.
2. Fully open both valves on manifold gauge set. Operate evacuation pump until vacuum reading of at least 28-29 in. Hg on low side is obtained. If specified reading cannot be reached, check for defective evacuation pump or leak in A/C system or gauge set. Repair or replace components as necessary.
3. Continue operating evacuation pump for 5 minutes after reaching 28-29 in. Hg. Close both valves on manifold gauge set. Stop evacuation pump. Observe low-side gauge. Any loss of vacuum indicates a system or gauge leak.
4. If leak is indicated, charge system with 8 ounces of R-12, and perform leak testing procedure. See LEAK TESTING. Repair any leaks, and repeat evacuation procedures.

R-134a

Information is not available from manufacturer.

CHARGING A/C SYSTEM

Note. Manufacturer does not recommend using one-pound cans. Using a charging station will allow precise measurement of refrigerant charge. See REFRIGERANT OIL & REFRIGERANT SPECIFICATIONS tables in the A/C COMPRESSOR SERVICING article for system capacities.

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 connected (from evacuation procedure), start engine, but DO NOT turn on A/C. Connect refrigerant drum to hose on center connector of manifold gauge set. Invert refrigerant drum for liquid charging. Open low-side gauge valve on manifold gauge set. Allow 16 ounces of refrigerant to enter system.
2. When 16 ounces of refrigerant have entered system, turn A/C system to normal operating position with blower fan on high speed. Continue charging (liquid charging) until proper amount of refrigerant has entered system.
3. Close refrigerant 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. See LEAK TESTING.

LEAK TESTING

Operate system to stabilize high-side and low-side pressures. Turn engine off. Using a refrigerant leak detector, check all refrigerant line connections for leaks. Check compressor seal area and condenser.

Refrigerants are heavier than air. Always check for leaks at bottom of refrigerant lines and components. Refrigerant oil will leak with refrigerant. Visually check all connections and compressor clutch area for oil stains. If compressor shaft seal is leaking, a fresh oil streak will normally be seen on underside of hood, above compressor clutch.

Always perform leak testing after A/C service. Move refrigerant leak detector slowly to check for leaks, as leaks will not be detected if leak testing is performed too quickly.

See also:
• A/C COMPRESSOR SERVICING
• A/C COMPRESSOR REFRIGERANT OIL CHECKING