High RPM with A/C On

[bhogue18@yahoo.com]

1999 Ranger, 2.5L I4, Manual Transmission, 197K miles

After driving for a few minutes, the a/c will blow warm and, when I put the clutch in, the RPM's will stay around 2000. When I turn the a/c off, the RPM's go down to around 800 (dash gauge).

I have used a new IAC valve and a new throttle position sensor to no avail. I have not found any vacuum leaks that might be causing the problem.

Not sure what is going on. Any help appreciated.

 

[onlyme]

Have you checked the vacuum lines to the vacuum canister in the passenger inner fender? I had to replace 1 of mine because it was brittle and had cracks in it and was causing an issue. Does your max ac blow warm also? If it does Id check the heater control valve to see if it's working properly, and also check the vacuum line to the heater control valve, mine needed replaced.

 

[tomw]

The IAC is supposed to add some 'idle bump' to compensate for the load of the A/C compressor. If the compressor is disengaging, the idle would increase until the computer caught onto the increased rpm.
When it starts to blow warm air, pull over, open the hood, engine at idle and look at the A/C compressor, right at the front, where the belt is. The 'center' of the compressor should be turning if there is enough A/C load{HOT outside, not cool} to keep the compressor busy. If it is not turning, there are two major reasons: 1)low refrigerant and 2) bad clutch or too large a clutch gap. The clutch is the A/C clutch in the center of the pulley. It 'grabs' when the A/C is on, and lets the pulley free-wheel when the A/C is off. If the gap is too big, it may not be able to pull the clutch together all the time.
Low refrigerant is noted by the LPCO switch on the accumulator. Get your pressures checked.
You can, if adventurous, use a broomstick to poke the center of the clutch to see if 'helping' it draw the parts into connection works. If so, the gap may be too big. It is adjustable by moving 'shim' washers from front to rear or vice-versa on the compressor drive shaft.
tom

 

[bhogue18@yahoo.com]

It will blow cold in max a/c for a while and then blows warm. When it starts blowing warm is when the engine rpm's will not drop below 2000 until I turn the a/c to off. I did a leak check through the vacuum canister to the interior vacuum control valve and there was no leaks.
Not sure why the pcm wants to maintain a high rpm?

 

[onlyme]

There is a vacuum line that runs from the engine to the vacuum canister, and another vacuum line that runs from the canister to the firewall. On the firewall though there is an additional white/grayish vacuum line coming from the firewall up to the heater control valve, and it does not run to or from the vacuum canister. You can follow that vacuum line from the heater control valve back to the firewall. On my 98 that vacuum line had small cracks in it and caused a vacuum leak. You can't really see that vacuum line well without removing the inner fender which is fairly simple to do. On max ac that vacuum line operates the heater control valve.

 

[tomw]

Does the A/C clutch turn all the time or does it stop now and again?

If you cannot answer that, you have chosen to ignore a basic piece of troubleshooting data. Your choice.

 

[bhogue18@yahoo.com]

Thanks for all the help. It turned out to be the air gap on the compressor clutch. There was a .055" gap so I jumpered the field coil and it engaged the clutch but with a faint 'clank'. I removed the one and only spacer and now there is a much more pronounced sound. Test drove over the past two days and no problems.

@TomW I was unable to duplicate the high rpm condition in a convenient place to observe the compressor. But I did observe it when the the a/c would blow warm and the clutch was not engaged. The high rpm through me for a loop. Thanks for pointing me in the right direction.