A/C Compressor cycling. Is this normal?

[IS300E30]

I just replaced a defective remanufactured a/c compressor because it was leaking like crazy. The thing is on that compressor when the a/c was turned on the a/c clutch would spin continously until you turned off the a/c compressor.


Now, the new a/c remanufactured compressor that I just had put on is different. When you turn on the compressor it turns on then kicks off for around 7 seconds (havent timed it yet) then cycles back on for a few seconds and then cycles back off for 7 seconds and so on and so forth.
Is this normal or not?


Which way is normal?


Please help, but only if you have true knowledge of how our a/c compressor clutch is supposed to work.

[bmwstephen]

I think thats how AC works. There is an AC switch on your receiver/dryer that sends a voltage to disconnect and reconnect the AC clutch so your system doesn't get too cool to the point it freezes

[Ryann]

Your new compressor is short cycling which usually occurs because your system is low on refrigerant. Suction pressure on the inlet side of your compressor quickly drops while the compressor is running causing the low pressure switch at the drier to open, de-energizing the compressor clutch. Short cycling can also occur when the high pressure switch is opening. High discharge pressure can be caused by atmospheric air in the system that was let in while the system was opened and not properly evacuated, an overcharged system, or by a lack of air flow over the condenser coil.

bmwstephen- e30's have an evaporator temperature switch inside the car that does what you're talking about.

[IS300E30]

I went back to the shop. The mechanic belives it is an unfair test right now as it is around 40 degrees outside and with the wind factor around 25 degrees.

The a/c hose that is supposed to be cold is cold. The vents is shooting out really cold air.

He says that it is so cold outside that the a/c system is cycling on/off as it knows it is too cold to be running a/c fully.the a/c clutch turns on, then stops then slowly moves (really slowly, hard to see its moving) this happends in seven second intervals then kicks back on for a few seconds then stops and goes to the seven second interval and kicks back on and so on and so forth.

The mechanic says he would not be surprised if it gets a little warmer later today that the interval extends a little longer then seven seconds.

And when it get warm outside 80 degrees and up or around there it will be on constantly.

He said he would put more R134a in if I liked but he does not believe thats the problem and he rather me leave it alone until it is warm enough to really test it.

I do have a year warranty in parts/labor.

Thoughts?

[IS300E30]

Read the Bentley and it states this:



"The compressor is engaged by an electro-magnetic clutch that is actuated when the A/C is turned on. The thermostat switch automatically disengages the clutch when the temperature in the passenger compartment reaches the level set on the operating controls."



Reading this, it seems like the a/c clutch is doing like it is supposed to do since it was so cold the other day? Am I crazy, or am I reading this right and maybe the mechanic is right and the a/c compressor clutch is working like it is supposed to?

[Ryann]

You could test his theory by turning on the heat full blast for a while to warm up the interior, then switch over to a/c. You could even use the temp. dial to open your heater valve while the a/c is on, which should keep the evaporator warm enough to force the evaporator temperature switch to remain closed and compressor clutch engaged.

He very well may be right though. In my initial response to your question I made the assumption that your compressor was short cycling in warm conditions.

[IS300E30]

You could test his theory by turning on the heat full blast for a while to warm up the interior, then switch over to a/c. You could even use the temp. dial to open your heater valve while the a/c is on, which should keep the evaporator warm enough to force the evaporator temperature switch to remain closed and compressor clutch engaged.

Thank you for the quick response.

Can you give a little more detail how this

"You could even use the temp. dial to open your heater valve while the a/c is on, which should keep the evaporator warm enough to force the evaporator temperature switch to remain closed and compressor clutch engaged."

is done?

I think you are reccommending to turn on the heater AND the cold a/c at the same time. if so, how do you do that?

[Ryann]

Turn your a/c on but turn your hot/cold knob to hot.

[IS300E30]

Turn your a/c on but turn your hot/cold knob to hot.

So, press the blue snow flake button and turn the hot/cold knob to hot and that will turn the a/c on and the heat on? That is also safe for the system?

[Ryann]

Yes. It won't hurt anything. After the car is warm and you've got heat blowing out of the vents the compressor shouldn't cycle if your mechanic is right. If he's wrong then it's the pressure switch causing short cycling.