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Discussion Starter · #1 ·
When I sit at idle, or go less than 15 mph, the air conditioner works great. But if I get up to 20 or above, it quits working and blows hot like I turned the A/C switch off. I have changed batteries recently. It did it before and after. So bu changing the battery, it should have reset the ECM if there was a problem there. And the battery was out for about 2 hours as I pulled it then went and bought a new one so I didn't have to go back for the core charge.

Any ideas? Getting warmer
 

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I think you will need a shop. Your system will have high and low pressure cut off sensors. If you are getting either high pressure or low pressure cut offs you need to find out if it is a sensor failure or if you actually have high or low pressure. Some cars are set up for the electrical system to shut off the compressor if the engine is having to work too hard like climbing a mountain. If you just start changing parts, you might get lucky or you might just spend a fortune in new parts that don't fix it. My Magnum was cooling fine for the driver's side, but my wife complained that her side of the car was not getting cold. It turned out that I had leaks at the shrader valves in the suction & discharge ports. If your engine overheats, the computer will possibly chut off the ac to help keep it cool. You could have a freon leak, or moisture in the system. I've probably toalk about lees than 10% of the possible problems. Take it to a shop to have it checked out by a professional.
 

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Ac systems are not that complicated if you have a complete wiring diagram. In my 30+ years as a refrigeration mechanic, I found most people immediately replace the expansion valve if it quits cooling, but it is almost never the expansion valve. Put a set of gages on the system and check suction and discharge pressures at idles with the ac working. Then have someone rev the engine a bit to see if the compressor clutch disengages. If it disengaged, what were the pressures? Typically, a low-pressure cutout is set somewhere around 10#. The high-pressure cutout will open at @300#. If your pressure is below 10# and it cuts out or above 300# and it cuts out, you have a problem. High pressure is caused by something blocking airflow through the condenser, non condensables (air) in the system, or a restriction such as a pinched line between the compressor & the condenser. Low pressure is caused by a restriction between the evaporator and the compressor, moisture in the system (one drop of water freezing in the expansion valve will stop the flow of freon through the system until the ice melts), low freon charge (look for leaks before adding freon-freon is an oil magnet, look for oil on lines, use soap bubbles on any fittings or Schrader valves), lastly low freon pressure could be caused by air flow restrictions in the evaporator coil.
 

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Discussion Starter · #5 ·
Well, as weird as it may sound, I think it was like a high pressure switch that was stuck. It must have worked its self loose as it blows super cold now. As good as ever. Thanks for all the tips. Might come in handy in the future. I do want to get a set of gauges and learn how to use and read them
 

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Sounds like moisture in the system. One drop of water freezing in the expansion valve will cause the unit to quit cooling. Once the ice thaws the unit will start cooling until that drop gets back to the expansion valve and freezes again. You need to pump down the system and replace the receiver/drier.
 
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