A/c System General Servicing: Diagnosis Dodge Cab & Chassis Dakota

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.

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.

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.

Scheme 1

Compressor - Cycles on and off too fast.

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

Scheme 2

Compressor - Cycles at incorrect temperature or pressure.

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

Scheme 3

Discharge Air - Slightly cool.

Sight Glass - Some bubbles.

Scheme 4

Discharge Air - Warm.

Sight Glass - Clear or Oil Streaks.

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

Scheme 5

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.

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.

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.

Scheme 6

Compressor - Noisy.

Scheme 7

Discharge Air - Warm.

High Side Lines - Very Hot.

Sight Glass - Bubbles.

Scheme 8

LEAK TESTING ALL MANUFACTURERS

Operate system to stabilize high and low side pressures. Turn engine off. Using an R-12 leak detector, check all refrigerant line connections for leaks. Check compressor seal area and condenser. R-12 is heavier than air. Always check for leaks at bottom of refrigerant lines and components. Refrigerant oil will leak with R-12. 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 R-12 leak detector slowly to check for leaks, as leaks will not be detected if leak testing is performed too quickly.