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Old 09-06-2013, 03:25 PM
Mike In Bama Mike In Bama is offline
Electronics Tech
 
Join Date: Mar 2013
Posts: 1,194
Default AC Troubleshooting

I'm reading a book for ASE Certification in Heating & AC. I've come across several tips that might be handy. I'll be adding to this soon.



With a vehicle off, the High and Low gauges should read equal. (About 71 psi at 70*)

To find leaks, there must be at least 50 psi in the system.

First, start the engine. Turn the AC on and off to listen for the compressor clutch. If you can't hear it or there is no change in RPM, there is a problem with the electrical control circuit or the system is low on refrigerant.

Bad compressor bearings won't make noise until the clutch is engaged, but bad clutch bearings will make noise all of the time the engine is running.

Clicking or buzzing noise from the compressor indicates an overcharge and liquid is entering the compressor. That needs to be corrected immediately! Other noise may indicate air in the system.

Knocking or rattling usually indicates internal compressor damage. However, loose mounting can also produce this.

MAP and MAF sensors are also engine load sensors. If dirty they could fool the PCM into not operating the compressor.

A bad Power Steering Pressure switch could do the same thing.

A dirty TPS could make the PCM think you have the gas pedal much closer to the floor than you do, cutting the compressor off.

A bad Engine Coolant Temperature sensor could signal that the truck is boiling over. That would be a bad time to put the load of a compressor on it, so it won't.

Even the Ambient Temperature sensor can bring things to a halt. If the weather is too cold, the oil in the compressor will thicken and not protect it properly. You won't get it to kick in. (I believe, but haven't proven yet, that this is built in with the MAF sensor)

2005 2.3L XL Electronics Tech since '70's
__________________
2005 2.3L XL 5SOD 3.73 K&N
KYB Shocks Husky Toolbox
Alpine / Rockford Fosgate Sound

"Ask me about my AC Vent fix!"
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  #2  
Old 09-06-2013, 03:57 PM
Mike In Bama Mike In Bama is offline
Electronics Tech
 
Join Date: Mar 2013
Posts: 1,194
Default

[QUOTE="Mike In Bama;1664791"]I'm reading a book for ASE Certification in Heating & AC. I've come across several tips that might be handy. I'll be adding to this soon.

With a vehicle off, the High and Low gauges should read equal. (About 71 psi at 70*)

To find leaks, there must be at least 50 psi in the system.

First, start the engine. Turn the AC on and off to listen for the compressor clutch. If you can't hear it or there is no change in RPM, there is a problem with the electrical control circuit or the system is low on refrigerant.

Bad compressor bearings won't make noise until the clutch is engaged, but bad clutch bearings will make noise all of the time the engine is running.

Clicking or buzzing noise from the compressor indicates an overcharge and liquid is entering the compressor. That needs to be corrected immediately! Other noise may indicate air in the system.

Knocking or rattling usually indicates internal compressor damage. However, loose mounting can also produce this.

MAP and MAF sensors are also engine load sensors. If dirty they could fool the PCM into not operating the compressor.

A bad Power Steering Pressure switch could do the same thing.

A dirty TPS could make the PCM think you have the gas pedal much closer to the floor than you do, cutting the compressor off.

A bad Engine Coolant Temperature sensor could signal that the truck is boiling over. That would be a bad time to put the load of a compressor on it, so it won't.

Even the Ambient Temperature sensor can bring things to a halt. If the weather is too cold, the oil in the compressor will thicken and not protect it properly. You won't get it to kick in. (I believe, but haven't proven yet, that this is built in with the MAF sensor)


Interpreting Gauge Readings

Low side normal, High side normal (But Poor Cooling)
- Air or moisture in system
- Blend door stuck open
- Defective or misadjusted Thermostatic switch
- Defective Pressure Cycling switch

Low side low, High side low
- Low refrigerant charge (possible leak)
- Expansion valve stuck closed
- Restriction on the high side

Low side high, High side high
- Damaged compressor (bent or damaged valves)
- Refrigerant overcharge
- Condenser restriction or inoperative fan
- Expansion valve stuck open

Low side high, High side low
- Damaged compressor (bent or damaged valves)
- Loose drive belt or slipping clutch (if no compressor noise)

Low side low, High side normal to high
- Expansion valve stuck closed
- clogged orifice tube

Common causes of high pressure
- Refrigerant overcharge
- Restricted condenser (leaves, paper, bugs, etc)
- Clogged receiver/drier
- Plugged orifice tube

2005 2.3L XL Electronics Tech since '70's
__________________
2005 2.3L XL 5SOD 3.73 K&N
KYB Shocks Husky Toolbox
Alpine / Rockford Fosgate Sound

"Ask me about my AC Vent fix!"
Reply With Quote
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