Air conditioner problem
 

I finally replaced the clutch on my AC. It is cooling well. Works fine at idle and around town but when i get out on the highway between 55-65 it freezes up.

Any Ideas?

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Does the ac continue to work when the ice forms on the outside of the pipes?

Jim

Do you have condensor coil cooling fans. Do you have a seperate relay to turn on your fans or is it common with your compressor clutch relay. I had the same problem with an old air system. The fan motors are permenant magnet motors, at highway speeds the blades are driven by the wind and the motor becomes a generator. It produced enough power to hold the clutch in and freeze everything up. I added another relay to isolate the fans from the clutch and have had no problems since. Don't ask how long it took to figure this one out. Steve

No it slowly looses air flow. I have to tun off the AC and let thaw out.

I have electic fans on my truck. But I don't think it has anything to do with my problem. When the AC is on the cluch on my system does not cycle on and off.

Could be a low on refrigerent this will cause the evaporator to freeze up. Might try adding a small amount at a time to see if it helps.

I could be wrong but it sounds like a POA valve problem.

Clutch on our trucks is engaged continuosly when a/c is selected. Evaporator freeze-up in a properly functioning system is prevented by the poa (pilot operated absolute) valve.

I am too new to A/C to arm chair diagnose your problem. You can try asking over in the a/csource forum. Be prepared to provide high/low gauge readings though.

I agree with zeke. Check for low refrigerent. That has happened to me before.

Freezing can be caused by an overcharge condition, not an undercharge. Low airflow at the evaporator or condenser can also cause freezing. Seeing as you probably have plenty of airflow across the condenser at highway speeds- that is out. Leaves and other crud coming in through the cowl can clog the evap coil. A sticking POA valve is another definite possibility. Check the airflow in the cab at all fan speeds. if it is fine probably the POA.

I had same problem, replaced expansion valve and it did not cure problem. Tried to find new POA valve but they are not avail. Repaced POA valve with an adjustable valve that cycles the compressor off before evap. freeze up. Works fine now.

Just to be clear (I am an AC novice), the compressor does not cycle on and off if the truck has a factory set-up? If that is so, isn't that unusual compared to the way most vehicles' AC behaves?

You ar correct, as I am an A/C novice myself, I asked this same question when I was getting ready to recharge my system after re-installing a new compressor. My system was bone dry and I turned on the A/C and the compressor stayed engaged. This as I was told is normal function for these model year trucks. There is a single switch that supplies power to the compressor clutch and when this switch is made the compressor stays on always.

You can get a poa eleminator kit that will turn your system to a cycling clutch. Old air products. Around $100.