For 1990-2009 cars

Symptoms | Cause | Correction
--- | --- | ---
Low side: vacuum reading at times, then normal pressure | Receiver/Drier oversaturated with moisture freezing at expansion valve orifice causing temporary stop of refrigerant flow. Normal refrigerant state is restored after ice melts at expansion valve. |

1. Replace receiver/dryer.

Refer to Receiver Dehydrator Replacement

2. Remove moisture in refrigeration system though repeatedly system evacuating.

Low side: pressure below specifications Hi side: pressure below specifications Sight glass: bubbles observed continuously | Insufficient refrigerant due to leakage within the refrigeration system. | Locate and repair refrigerant leakage. Refer to Leak Testing
Low side: vacuum reading High side: pressure extremely below specifications Frost/dew on pipes to receiver/dryer, expansion valve | Restricted flow of refrigerant due to:

• | Obstruction by moisture or dirt.

• | Broken expansion valve's heat sensing tube

1. Inspect expansion valve's heat sensing tube location.
2. Remove and inspect expansion valve. Clean dirt in expansion valve by blowing clean, unlubricated ship air or replace expansion valve if clean.
3. Replace expansion valve if heat sensing tube is broken.
4. Replace receiver/dryer.

Refer to Thermal Expansion Valve Replacement

Low side: pressure above specifications Hi side: pressure above specifications Sight glass: no bubbles observed, even after lowering engine speed from 1500 to 850 rpm | Two possible causes:

• | Refrigerant system is overcharged.

• | Condenser unable to cool air due to clogged fins and/or inadequate blower output.

1. Inspect condenser. Clean if obstructed.
2. Inspect blower operation.
3. If condenser and blower OK, check amount of refrigerant. Charge to proper amount.

Low side: pressure above specifications Hi side: pressure above specifications Sight glass: bubbles observed Evaporator-to-compressor pipe feels hot | Air inside refrigeration system due to insufficient vacuum purging. | Evacuate and recharge refrigeration system. Inspect compressor oil if dirty or insufficient. Refer to Refrigerant Recovery and Recharging
Low side: pressure above specifications Hi side: pressure above specifications Frost/dew on evaporator-to-compressor pipe | Excessive refrigerant flow due to malfunctioning expansion valve that opened too wide or improper heat sensing tube location. |

1. Inspect heat sensing tube for proper location.
2. If heat sensing tube OK, replace expansion valve.

Refer to Thermal Expansion Valve Replacement

Low side: Pressure above specifications High side: pressure below specifications | Leaking valve/broken parts inside compressor causing low refrigerant compression. | Replace compressor. Refer to Air Conditioning Compressor Replacement .