1991 AC & RPM question

[tsr2185]

Got a odd question...

My compressor blew, so i got it unplugged at the compressor so it doesnt try and kick on when I put defrost on. I plan to completely overhaul the AC system and get it working this summer. When I hit the AC on button, the controls would show it was on, and I can feel/hear an increase in RPM due to this even though it was unplugged.

I noticed the other day, that the RPMs dont kick up anymore when I had accidently hit the AC button. Is this because the ECU doesn't sense the compressor plugged in, or is there something else wrong now?

I just want to make sure this is addressed before i spend $300 plus getting the AC all back operational.

Picture taken from google, as I am offshore for another few weeks.....

TIA

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[someotherguy]

The ECM is always monitoring idle speed and controlling it with the IAC; when the load of the A/C compressor causes idle speed to dip a little, the ECM tells the IAC to shore it up. With a non-functioning A/C, no dip in idle to correct.

Richard

 

[tsr2185]

The ECM is always monitoring idle speed and controlling it with the IAC; when the load of the A/C compressor causes idle speed to dip a little, the ECM tells the IAC to shore it up. With a non-functioning A/C, no dip in idle to correct.

Richard

thanks

It did for sure increase idle when the AC button was pressed while the compressor was unplugged before....

Just noticed it didnt do it anymore. This is about 6 months of it being unplugged.

 

[studigggs]

I believe there is a little more to it rather than just the IAC trying to maintain a fixed idle speed. When I unplug the compressor clutch the idle speed increases. There must be a feedback to the ECM when power is directed to the clutch cycling switch that calls for increased RPM.

 

[PlayingWithTBI]

There must be a feedback to the ECM when power is directed to the clutch cycling switch that calls for increased RPM.

^^^Yes - on my 88, when the A/C is turned on, the power goes through the Low Pressure Cycling switch (if it sees pressure) then to the Compressor Clutch and the ECM which then raises the idle. It will do that even with the clutch wire disconnected.

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If it was raising the idle then stopped you probably lost your Freon charge.

 

[tsr2185]

^^^Yes - on my 88, when the A/C is turned on, the power goes through the Low Pressure Cycling switch (if it sees pressure) then to the Compressor Clutch and the ECM which then raises the idle. It will do that even with the clutch wire disconnected.

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If it was raising the idle then stopped you probably lost your Freon charge.

I did have some freon left after it blew out the seal on the compressor. I did open up and check the orifice tube. I dont remember for sure if it started doing this just after i evacuated the system completely. This would make sense for sure.......