Unstable Gauge Readings

Test Results
1. Low pressure reading in normal but a vacuum is indicated during test.
2. High pressure reading is normal but falls when a vacuum reading is indicated on the low pressure side.
3. Air at center vent nozzle is cold until a vacuum is indicated on the low pressure side, then becomes warm.

Cause
Large amounts of moisture in system. Drying element in receiver/dryer is saturated with moisture and is releasing moisture into A/C system when ambient temperatures are high. This moisture freezes in the expansion valve, blocking it, and prevents refrigerant from flowing to evaporator.

Correction
1. Drain A/C system.
2. Replace receiver/dryer.
3. Evacuate A/C system.
4. Fill A/C system.
5. Perform operational test.