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.
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
the only reason)is that the AC is undercharged. Some cycling in cold weather is
with the compressor running for a fwe seconds and then staying off for a period
time. The on\off time depends on ambient temperature,interior temperature,and
humidity. Rapid cycling like yours usually indicates a low refrigerant charge.
'94, being 11 years old,is probably due for some AC system work.
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
tom @ www.Love-Calculators.com
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