Use of Pressure Gauges For A/C Diagnosis - Refrigerant System
Use of Pressure Gauges For A/C Diagnosis:
COMPLAINT:
Cooling is not adequate.
CONDITION:
- Discharge air slightly cool.
- Gauge readings normal.
- Occasional bubbles.
DIAGNOSIS:
- Air or moisture present in the system.
CORRECTION:
1. Leak check the system.
- Examine the compressor seal area for evidence of excessive oil leakage.*
2. Recover the refrigerant from the system.
3. Repair any leaks.
4. If the conditions described in "Receiver/Dryer Replacement"exist, replace the receiver/dryer.
5. Evacuate the system for a minimum of 30 minutes** and recharge it.
6. Operate the system and check its performance.
*Minor oil seepage is normal.
**Longer periods of applied vacuum are better.
COMPLAINT:
Cooling is not adequate during the hot part of the day.
NOTE: Cooling may be satisfactory during the early morning or late evening hours.
CONDITION:
- The low-side gauge reading is normal but may drop into vacuum during testing.
- The high-side gauge reading is normal but drops when the low side gauge reading drops into vacuum.
- The sight glass may show tiny bubbles.
- The discharge air from the evaporator is sharp and cold but becomes warm when the low-side gauge reading drops into a vacuum.
DIAGNOSIS:
- Moisture in the system. Moisture may be freezing in the expansion valve orifice.
CORRECTION:
1. Recover the refrigerant from the system.
2. Replace the receiver/dryer.
3. Evacuate the system for a minimum of 30 minutes* and recharge it.
4. Operate the system and check the performance.
*Longer periods of applied vacuum are better.
COMPLAINT:
Little or no cooling.
CONDITION:
- The low-side gauge reading is low.
- The high-side gauge reading is low.
- There is a stream of bubbles evident in the sight glass and oil streaks.
- The discharge air from the evaporator is warm or only slightly cool.
DIAGNOSIS:
- The system is low on refrigerant. This may be caused by a small leak.
CORRECTION:
1. Charge the system and perform a leak check.
2. Recover refrigerant from the system if it is necessary to replace components or lines.
3. Repair any leaks.
4. If the conditions described in "Receiver/Dryer Replacement" exist, replace the receiver/dryer.
5. Evacuate the system for a minimum of 30 minutes* and recharge it.
6. 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 very low.
- The high-side gauge reading is very low.
- There is no liquid or bubbles evident in the sight glass.
- The discharge air from the evaporator is warm.
DIAGNOSIS:
- The system is excessively low on refrigerant, probably due to a serious leak.
CORRECTION:
1. Leak check the system; add a partial refrigerant charge before leak-testing to insure the leak check works.
- Examine the compressor seal area for evidence of excessive oil leakage.*
2. Recover the refrigerant from the system.
3. Repair the leaks.
4. If a serious leak was present, replace the receiver/dryer.
5. Evacuate the system for a minimum of 30 minutes** and recharge it.
6. Operate the system and check its performance.
*Minor oil seepage is normal.
**Longer periods of applied vacuum are better.
COMPLAINT:
Cooling is not adequate.
CONDITION:
- The low-side gauge reading is low.
- 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 heavy 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 conditions described in "Receiver/Dryer Replacement" 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 low.
- The high-side gauge reading is too low.
- The discharge air from the evaporator is only slightly cool.
- The liquid line is cool to the touch; the line on the receiver/dryer may show heavy sweating or frost.
NOTE: a change of state occurs too soon due to the restriction.
DIAGNOSIS:
- There a a restriction in the receiver/dryer, or the liquid line. The compressor is removing refrigerant from the evaporator faster than it can enter, resulting in a "starved" evaporator.
CORRECTION:
1. Recover the refrigerant from the system.
2. Remove and replace the receiver/dryer; the liquid lines, and other defective parts.
3. Evacuate the system for a minimum of 30 minutes* and recharge it.
4. 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 too high.
- The high-side gauge reading is too low.
- The sight glass is free of bubbles; the system is fully charged.
- The discharge air from the evaporator is not sufficiently cool.
DIAGNOSIS:
- There may be a leak in the compressor, or the drive belt may be loose/worn. The compressor pistons, rings, 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 receiver/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:
Little or no cooling. The engine temperature may be high.
CONDITION:
- The low-side gauge reading is excessively high.
- The high-side gauge reading is excessively high.
- Bubbles may appear occasionally in the sight glass. 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.
Refer to basic checks in "Verified System Malfunction Follow-Up".
CORRECTION:
1. Recover the refrigerant.
2. Recharge the refrigerant according to the underhood label or the specifications in the 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:
COMPLAINT:
Little or no cooling.
CONDITION:
- The low-side gauge reading is too high.
- The high-side gauge reading is too high.
- The discharge air from the evaporator is warm.
- The low-side hose to the compressor shows heavy sweating.
- When the system is started, there is little or no pressure change.
DIAGNOSIS:
- The expansion valve is stuck open allowing too much refrigerant into the evaporator, causing flooding.
CORRECTION:
1. Recover the refrigerant from the system.
2. Replace the expansion valve.
3. If the conditions listed in "Receiver/Dryer Replacement" exist, 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.
COMPLAINT:
Little or no cooling.
CONDITION:
- The low-side gauge reading is too high.
- The high-side gauge reading is too high.
- There are occasional bubbles in the sight glass.
- The discharge air from the evaporator is warm.
DIAGNOSIS:
- There is air in the system. The refrigerant is contaminated by non-condensable material (air and/or moisture).
CORRECTION:
1. Leak-check the system.
2. Recover the refrigerant from the system and repair any leaks found.
3. Replace the receiver/dryer, which may be saturated with moisture.
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.