Air conditioner temperature inconsistent - hot, cold, ambient

[azshelby350]

I searched the forums but couldn't find a good thread, besides various mentions of people having A/C evaporator and/or condenser issues. Pardon my ignorance of the A/C system to be able to better self-diagnose what's happening ...

As the title says, the A/C in my Ford Racing school car is completely inconsistent. Sometimes it works and blows cold air (or the appropriate temp based on the dial position), sometimes it blows what feels like vent/ambient temp air, and sometimes it blows downright hot air. I drove it today at varying speeds and loads and I do notice a correlation between load and steady throttle. The A/C temp seems to be more consistent at freeway speed and steady throttle, or at idle. Accelerating makes it blow hot air only most of the time. It's already getting warm here in Arizona (about 86F today) so I'd like to determine if the compressor clutch is the culprit or what.

Please note that the school cars all had their air disconnected for their whole life on track, so I do not know the affect that had on seals, gaskets, freon charge, etc. The school hooked the system back up before delivering to owners like me.

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[mrgooden]

Gone are the days of R12 unfortunately. But, many things effect your temperature with modern day refrigerant. To cool well, you have to have good airflow across the condenser. Hense most cars cool best traveling and why radiator fans kick on when you turn the AC.

If your car is accelerating hard, the compressor is usually turned off and kicks back on when you let off the throttle. If your temperature is varying under no load conditions, you should hook up a set of refrigerant gauges and see what your pressures are reading. If you end up having low pressures, you may have a small leak and require some servicing.

If pressures are correct, you could have a failing compressor, although gauges can help you identify that, or you could have a failing expansion value. That is obviously not the only thing it can be but, step one should always be gauges.

I primarily worked on external aircraft air conditioners using about 130 LBS of R22.

My 2 cents

Richard

 

[526 HRSE]

Sounds like a clutch. Once you lose freon, it's not going to get hot, cold, hot cold. I'll have to dig up the paperwork, but i took mine in last year and it ended up being something minor like a relay or something.

 

[Lurker_350]

I would first check your refrigerant pressures. Ford has a really nice set of temperature dependent suction and discharge pressures in chart form.

Discharge Side:

Suction Side:

My A/C was doing what you are describing last year and I tested the pressures according to the workshop manual. Turned out the refrigerant was just a little low, such that when you increased engine RPM and airflow across the condenser, it would cool as it should, but at low engine and vehicle speed, it wouldn't.

I never figured out where the refrigerant "leaked", but adding a bit until the suction and discharge pressures were in the right spot has kept it operating correctly for over a year. Note that Ford also puts in dye at the factory, so a large leak should be apparent using a UV light and glasses. I couldn't find mine.

Hopefully your issue is as simple as mine was.

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