Use of Pressure Gauges For A/C Diagnosis - Refrigerant System

AMBIENT TEMPERATURE/RELATIVE HUMIDITY REFERENCE CHART






COMPLAINT:

Cooling is not adequate.

CONDITION:







- The low-side gauge reading is low, or may go into a vacuum.
- The high-side gauge reading increases as the system operates.
- The discharge air from the evaporator is only slightly cool.
- The expansion valve inlet may show heaving sweating or frost.
- The high-pressure side is abnormally hot.

DIAGNOSIS:

- The expansion valve is stuck closed; or is plugged by moisture, ice, or foreign material.

CORRECTION:

1. Recover the refrigerant from the system.
2. If the condition described exist, replace the receiver/dryer.
3. Evacuate the system for a minimum of 30 minutes* and recharge it.
4. Operate the system and check its performance.
5. If the system fails to function correctly, replace the expansion valve.

*Longer periods of applied vacuum are better.

COMPLAINT:

Cooling is not adequate.

CONDITION:







- The low-side gauge reading is too high.
- The high-side gauge reading is too low.
- The sight glass is tree of bubbles; the system is fully charged. (If equipped)
- The discharge air from the evaporator is not sufficiently cool.

DIAGNOSIS:

- There may be a leak in the compressor, or the drivebelt may be loose/worn. The compressor pistons, rings, valves, or cylinders may be excessively worn or scored.

CORRECTION:

1. Check the compressor for noisy or knocking operation.
2. Recover the refrigerant from the system..
3. Remove and replace the compressor, if it is noisy/knocking.
4. Examine the condenser for metal fragments - clean if required.
5. Replace the receive/dryer.
6. Evacuate the system for a minimum of 30 minutes* and recharge it.
7. Operate the system and check its performance.

*Longer periods of applied vacuum are better.

COMPLAINT:

Cooling is not adequate.

CONDITION:







- The low-side gauge reading is excessively high.
- The high-side gauge reading is excessively high.
- Bubble may appear occasionally in the sight glass. (if equipped) The liquid line is very hot.
- The discharge air from the evaporator is warm

DIAGNOSIS:







- The system may be overcharged
- The condenser may not be operating properly.
- Air flow through the condenser may be poor. The [1][2]auxiliary fan may not be operating properly.

CORRECTION:

1. Recover the refrigerant.
2. Recharge the refrigerant according to the underhood label or the specifications in TIS.
3. Operate the system and check its performance.

If the gauge readings are still too high:

1. Recover the refrigerant.
2. Blow shop air through the condenser to check whether its passages are free. A condenser can be clogged by debris, such as fragments from a failed compressor valve or desiccant from the receiver/dryer. If the condenser passages are clogged, replace it. Determine what material clogged the condenser.
3. Replace the receiver/dryer.
4. Evacuate the system for a minimum of 30 minutes* and recharge it.
5. Operate the system and check its performance.

*Longer periods of applied vacuum are better