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:

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:

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 .