AC Compressor Cycling

[Ludigdrums]

How long is the AC Compressor supposed to stay engaged with the AC on. I know it's supposed to cycle, but at what intervals? Mine was unplugged and I thought the AC didn't work, but plugged it in and it works just fine now. My mechanic said to make sure it was cycling though, and I'm not sure that it is. What are the risks of this?

 

[69MyWay]

tempurature, and air flow over the system will affect the cycle speed.

Watch it at idle for a couple of minutes. It should cycle in and out once or twice. At the least, rev the motor and watch. They will often cycle out as the RPM comes up fast.

The best thing to do is put a gauge on it and watch the pressure drop.

What you don't want is it to cycle in and out and in and out every couple of seconds. That is bad.

 

[cruzer99]

You are low on freon. Have it recharged.

 

[DDLS3]

The compressor clutch should engage and disengage at fairly short intervals while at idle. If it engages for only a few seconds then you are likely low on freon. To confirm this, take a hand held thermometer and stick it into a discharge duct with the fan switch on high. You should see 36-40 degrees with the engine just above an idle. If the temp is much above this and the cycle time is only a few seconds then a pound of freon may revive your a/c. If you are still running R-12 then you have decisions to make as the cost is very high.

 

[Ludigdrums]

The clutch engages, I just don't think that it disengages. What could that mean? The air is definately cold.

 

[Ludigdrums]

Anyone know how the compressor is supposed to be wired. My connector has a green and black wire, with a little transitor of some sorts connecting them both. I don't know which wire is supposed to go on which terminal as the connector goes on both ways. The results are the same, the clutch engages and the AC is cold, but the clutch doens't cycle. I'm thinking maybe it's that little transistor thing or something. Any info would be great. THANKS!

 

[vettenick]

The a/c clutch doesn't care which way the connector is hooked up. Current will flow in either direction. That little gizmo is a diode. That prevents your computer from getting spiked every time the clutch engages or disengages. The diode must be hooked up correctly other wise it'll fry.
Clutch cycling time is dependent on outside air temperature and the temperaure inside the vehicle. On a "normal" day, 80 degrees, I would say 10-15 seconds on, and approximately the same off. If you're not cycling at all, you might be short a little freon. Cycling is dependent on the evaporator temperature being brought down to approximately 32 degrees. If it didn't cycle, the evaporator would freeze. The only way to tell if everything is OK is to hook up some gauges and check the pressures. Making sure the system is charged properly will extend the compressor's life.

 

[drsantos]

Does any one know the value of the diode used on the A/c clutch?

 

[drsantos]

A/C issues

Since your talking A/C maybe you can help...Whenever I turn the temp selection to AC, the 25 Amp fuse for the blower motor blows. If it's in the off or heat position the fuse is OK. any ideas?

 

[vettenick]

Sorry I did not respond sooner. There's only three items that receive power when you're in the a/c mode: the a/c clutch, the pressure cycling switch and the idle solenoid. I doubt the pressure cycling switch is the problem with the fuse blowing, but it could be the cause of your compressor not cycling off. The only way to tell is to use an a/c gauge to see if the low side pressure pulls down to 28 psi. At that point the switch should open and turn the compressor off until the pressure reaches 47 psi, at which the switch will close and turn the compressor on. This is what is called cycling. If the pressure pulls down below 28 and does not shut off, then the switch may be stuck. If the pressure does not pull down, you're probably short of freon. Now back to the fuse: Check the resistance of the idle solenoid which should be 23 ohms. The clutch should be 3.6 ohms at room temperature. If either one is lower than spec that's what's blowing the fuse. If both measure OK. then check for a shorted green wire that's going to the solenoid, pressure switch or a/c clutch. The diode is rated for about 400 volts.

 

[DDLS3]

Guessing that you may be miswired at the switch or the compressor clutch which appears to be on this same circuit has a short.

 

[drsantos]

Ac Blowing Fuse

Last night I disconnected the idle stop solenoid and the fuse no longer blows when I select AC, Will the AC work without the idle
stop solenoid, and is the solenoid defective?

 

[vettenick]

It sounds like the solenoid is your problem. All the solenoid does is raise the idle about 100RPM to compensate for the load of the compressor. If you can live without it, do it. I don't think it's that expensive-about $25

 

[DDLS3]

My engine will stall at idle without the rpm raised. All I can say is try it and see.

 

[jsinga]

If the AC is properly charged it WONT cycle it will only cycle to keep the evaporator from freezing up.
A cycling clutch orfice system is desigened to be charged where the compressor runs at optimum pressures all the time and it cycles because the low pressure cut off switch senses the pressure is low enough the temp of the evaporator will start to freeze.
If you put gauges on a normal system the low side pressure will stay around 30psi and the compressor will stay engauged. If it drops to low it will cycle off.
That diode it to prevent voltage spikes when the magnetic clutch engauges and disengauges.

JS

 

[vettenick]

Without getting into a long winded discussion....any system that's running properly will cycle. When the temperature drops, the pressure will drop along with it (that's physics). The fact that the pressure drops is indicative of a system that is able to handle the load. There are a few exceptions to the cycling...if ambient temperatures are very high,the system may not be able to cool efficiently, thus the system runs continuously at idle. But put more air through the condenser by driving the car or using a large fan while the vehicle is idling will help with the system's efficiency...then you'll see the system cycle. Check any service manual. They will even calculate based on ambient temperatures as to what the on/off cycling periods should be like.
As far as handling the idle problem, don't use the idle screw to compensate, otherwise your throttle position voltage will be too high. Then the computer will try to adjust by changing your timing and actually may make you run a little richer at idle. If you're stalling, gedt a replacement. Good luck!