AC question on 96 Mustang GT

96 mustang gt 4.6L
With the AC switch on vent or floor, everything is fine. Put the switch in AC mode, every five seconds, idle jumps up to 1100-1200 rpm for a second, then drops back to normal. Blower works
fine in all modes but no cold air.
I know I am going to have to take this to be serviced, just need an opinion whether it is the compressor or something less serious.
Thanks
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Max Lawler wrote:

Your compressor is cycling and if it does so every few seconds, it's a shure sign of low 134a in your system. Needs to be checked for leaks and recharged. Good luck.
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Max Lawler wrote:

It probably does this in Defrost mode also. It is caused by the AC compressor cycling and the IAC trying to hold the RPM steady. Most likely reason (of course, not the only reason)is that the AC is undercharged. Some cycling in cold weather is normal with the compressor running for a fwe seconds and then staying off for a period of time. The on\off time depends on ambient temperature,interior temperature,and humidity. Rapid cycling like yours usually indicates a low refrigerant charge. Your '94, being 11 years old,is probably due for some AC system work.             Tom Adkins
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wrote:

Now this is what I would do.
I would run the car, outside, and pop the hood. With all your windows open, and vents on fresh air, turn down the temp control, and turn on the a/c. Now watch the compressor. You should see the a/c compressor pulley engage when the clutch engerizes. See if it's cycling every 5 secs. If it is, you might have a low(or high) pressure problem. That is fixed by adjusting system presures.(which is only to be done by trained licensed individuals ;) ).
Now if the clutch engages, and stays engage, and the engine is still cycling, be prepared for something else. I use to have a engine that looped under heavy idle conditions(like when warming up, or a/c on). I found my pcv was cloged, and after a change it stopped the 'looping'.
imho,
tom @ www.Love-Calculators.com
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