What Makes A/C Compressor Turn Off&ON?

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  #1  
Old 04-20-05, 02:12 AM
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Angry What Makes A/C Compressor Turn Off&ON?

Hi Everyone,

I posted another question about a week ago about evacuating my AC. Well, I decided to get that done at a shop so I knew it was done right. I replaced the compressor, evaporator, and drier myself though. When I got my car back, the AC blows very cold. Problem is, it never shuts down I remember it used to turn the compressor on and off automatically every 30 seconds or so. Now it just runs forever, making frost form on the lines. What did I do wrong? I'd really like to avoid taking it apart again because then I'll have to pay to have it evacuated again. Any suggestions? BTW, it is a '97 Acura CL, pretty much exactly the same as a Honda Accord.
 
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  #2  
Old 04-20-05, 06:54 AM
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most vehicles use either a pressure switch or a temperature sensing bulb to kick compressor off when evaporator reaches a certain temperature to keep it from freezing up, the amount the clutch cycles will vary depending on how long the a/c has been running, and ambient outside temperature, and engine rpm as your a/c is more efficient at a higher rpm versus idle, per example if its 95 degrees outside the a/c compressor may never need to cycle with just the engine at idle but at higher rpm such as driving on the highway it would cycle, on a 80 degree day it would cycle more often as it reaches the pressure or temperature point at the evaporator faster.
if you evaporator is freezing up you will have very little airflow coming from your vents even when on high so im not sure you actually have a problem
 
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Old 04-20-05, 08:44 AM
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I guess I just remember that when the air functioned correctly, I would hear the compressor turn off and on when it was idling. Now it never seems to go off (obviosly I can't tell when on the highway). I also never remember frost forming on the lines inside the engine compartment. Now it forms frost. Maybe this is nothing to worry about?

There was a small wire, that lead what looked like a temperature sensor, that sat on the evaporator. Is this what turns the compressor off? Maybe I put it in wrong?

Any advise it greatly appreciated!
 
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Old 04-20-05, 09:08 AM
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I also never remember frost forming on the lines inside the engine compartment. Now it forms frost. Maybe this is nothing to worry about?
Sounds like your low on freon with frost .Or you can have noncondensables in the unit. I dont know if you have a TXV
valve in there or not that could be bad.

ED
 
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Old 04-20-05, 09:30 AM
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Originally Posted by Ed Imeduc
I dont know if you have a TXV valve in there or not that could be bad.
And that's exactly what I was worried about. I do have a TXV valve and to replace it would mean recharging it again! I don't think it can be low in refridgerant because I just had it filled and its holding the charge perfectly. Does the TXV valve control the compressor? I think the frost is forming because its running constantly. Do you think it never shuts off because of the TXV valve or the wired "bulb" that attaches to the evaporator?
 
  #6  
Old 04-20-05, 03:34 PM
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When you mean never shut off, do you mean it cycles even when the A/C is not selected? If that is the case, then it is an electrical problem. If you mean that the clutch never disengages, that (shooting from the hip) means that it is low on refrg. Some compressors do not "cycle" as in the clutch goes in and out, my compressor on the Grand Am all ways has the clutch out when in A/C, it internaly (sp) cycles. If it is electric, does the fan cycle on and off?
 
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Old 04-21-05, 02:07 AM
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Originally Posted by Cabot
If it is electric, does the fan cycle on and off?
That's a good point. The fan does not turn off and on either which most likely means it's an electrical problem. And to clarify, I mean when the AC is on, it doesn't cycle. It turns off if I turn the AC off but it never cycles off automatically when I have the AC on. I'm finding it hard to believe its low on refridgerant because I just had it charged after replacing everything and the pressure is reading fine. I guess I'm just looking for clarification that its an electrical sensor or the thermal expansion valve.
 
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Old 04-21-05, 03:27 AM
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That TXV valve dont work off electric. That bulb works off the temp of the coil.
I just had it charged after replacing everything and the pressure is reading fine. I guess I'm just looking for clarification that its an electrical sensor or the thermal expansion valve.

Low freon, noncondensables in there can all screw up the TXV valve.

ED
 
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Old 04-21-05, 03:38 AM
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Another thing to add to the ---could be wrong all the above is true also if the shimming on the new clutch is incorect then the clutch will stay on all the time. You have to have the proper clearence for the clutch to be able to kick out. check clearance for your model/feeler gaige between clutch and compressor.
 
  #10  
Old 04-21-05, 09:12 AM
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If you know, what are your pressures and what temp is it at the condensor? your fan(s) do not come on at all with a/c selected?
 
  #11  
Old 04-21-05, 01:08 PM
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pete try this little test while observing your compressor to see if it cycles out. Turn your AC on to MAX with blower on high run it for several minutes to egualize the system and cool the interior of your car as much as possible Now turn the blower to its lowest setting and close off all the dash vents that you can. This should be done in the shade when the ambient temp is below 80f. If you have gauges have them on the car also so you can check the readings, what we are trying to do is cool the evaporator below the level that it should cycle out the compressor. If you do this with gauges and you see the low side setting in the low teens or below and the compressor does not cycle out your problem is most likely the TXV sensing bulb perhaps it fell out of the coil fins or shifted a bit and is not getting proper temp readings. If you can pull the blower and access it, move it to a different location in the coil and make sure it fits in tightly. while you have it accessible try to stick it to a ice cube and see if it cycles the compressor out, if so, you just have to find the right spot in the coil. Move closer to the inlet pipe and you should receive better readings. Good Luck
 
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