QuestionQUESTION: Hi,my AC works fine until the engine warms up to normal driving temp(slightly lower then mid point on temp gauge) then it cuts out.When the engine cools down the AC kicks on,and again cuts out when the engine warms up.The heater works fine. I have done the following-took the car to Chrysler they replaced the expansion valve-this did not correct the problem 2,Had all air removed from coolant system.again the problem still exzist.I have been told by mechanics that other sensors;other then AC sensors such as the coolant sensor could be telling the on board computer to cut the AC off, Is this a possibility? I think this is a common problem as my neighbor who owns a 01 Sebring has the same problem. I would appreciate any advise you might have regarding this problem. Thanks so much,Al
ANSWER: Hi Al,
The factors that control the compressor are: the mode control switch, refrigerant pressure transducer, evaporator probe, thermal limiter switch, compressor clutch relay, and the pcm.
I would set aside the mode switch, clutch relay, and pcm for the moment though they could be involved.
The pressure transducer will cut off the clutch from either too low or too high a pressure reading so that might be a cause of the problem if it was inaccurate (cutting off by misreading the pressure as being too high assuming that you don't have too low of a refrigerant charge).
When the evaporator temp sensor is too cold it will tell the pcm to turn of the compressor so that the evaporator doesn't freeze up. It could be misreading that temp. or have an inappropriate set point relative to the ambient temp. (that ambient value is only used in the ATC type of control panel). The turn off point depends upon the outside ambient temp as well so that sensor might be involved.
The engine coolant temp is also involved in allowing the compressor, so conceivably if that were misreading the temp it too could cause a cut off.
There is also a thermal limiter switch on the compressor which turns off the relay if the compressor surface temp gets too hot, but it should cycle on again after it cools down.
Those are the possible causes, along with the possibility of the relay being weak, of the mode switch faulty on the control panel, of even the pcm that intergrates it all.
You might look at the costs of the individual devices and the ease of install and pick the most practical for a do-it-yourself approach.
Does the unit cycle back on after a while? The answer to that might help narrow down the choices before throwing any more parts at it. Some of the devices can be monitored with the diagnostic readout box at a dealer or by measuring the voltage at the device. It is a bit too complex to try and tell you how to go through the process from a distance and I probably don't know everything needed.
Roland
PS Sorry for the delay but I just found your question in the 'pool'.
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QUESTION: Thank you Roland for your very speedy response. My next question to you,as I have spent almost a thousand dollars so far,is what is the easiest fix. Sounds like the thermal limiter switch would be relatively easy to get to and test.Is the pressure transducer located in the engine compartment? And could you please tell me the easiest place to start? I think the control anal is O.K.because when the engine is cool it seems to work fine,both heat and AC. To answer your question,the unit does not come on if the control panel is set to AC,however if I switch to heat and let it run on high fan for five minutes then switch back to AC, most times the compressor will kick in. I guess the last thing I want to do is go after the evaporator temp switch as this is a very involved,and costly process.
I think the next step is to go back to Chrysler and let them do another diagnostic(they told me they would wave the $280 diagnostic fee as I have already paid it once. Again,thanks so much for your help AL
ANSWER: Hi Al,
I am hearing two problems. At first you said it comes on and then the compressor quits as the engine warms up. Now you say that it does not come on (without reference to the engine temp) but that you have to run the heat on high fan for 5 minutes, then switch back to AC and then it will come on, most times. And then does it go off again?
As to where various items are located:
The pressure transducer is located in the return refrigerant line right at the point where it enters the compressor at the rear of the compressor on the engine side of it. It has a gray 4-wire plug with 3 actual wires.
The thermal switch on the compressor but the manual says it can't be replaced without replacing the compressor. Furthermore the manual doesn't show its exact location but the way it is described it appears to be in series with ac clutch actuation plug (which only has 1 wire and is near the pressure transducer (but the manual describes the switch as having 2 terminals??).
So that one I would let go on for now.
The evaporator temp sensor is not so bad as you might think according to the manual. I can xerox and postal mail the pages to you so you can see how it is done (you go in thru the glove box and the resistor block near the blower housing to retrieve it). That behavior involving running the unit on heat with the blower going makes me suspect it could be mis-reading the temp of the evaporator.
I guess I would opt for the free diagnostic of the system as otherwise you are still throwing parts at it. See if there is a clear answer from that effort and if not, then you are left with the parts throw. I would do the pressure transducer first and then the evap temp sensor.
Let me know if you want the instructions for doing those yourself. Let me know what you learn/want to proceed with.
Roland
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QUESTION: Hi again Roland,and thanks for your help. Well the AC ran fine all day Saturday and Sunday. Today,Monday it cut out once again at normal running temp,and again as soon as I put the heat on high for a couple of minutes and switched back to AC it ran fine without cutting out. I also noticed over the weekend,while it was running no water was dripping from the evap. drain. Took the car in today to my local mechanic and he checked the drain hose to see if it was plugged(the drain hose was not clogged) then he took a camera(not sure what this devise is called)and took a photo of the inside of the evap.There appeared to be something that looked like a small piece of foam at the bottom of the evap. housing. He thought this might be causing the problem by not allowing the evap to drain correctly and therefore effecting the evap.temp. sensor. Said he thought this was the problem and could fix it but he would have to remove the evap and open it to remove the blockage,estimated cost $800. Roland is there a way I can clean out the bottom of the evap.without taking it apart.(Maybe a shop vac or other devise) I would appreciate your thoughts on this. Also if I need to replace the evap.temp sensor via the removal of the glove box,I would appreciate any detailed input you might have on this as well. I do have a Haynes repair manual which explains how to remove the glove box. Again, I want to thank you for your Help Looking forward to fall and COOLER weather HA HA! Your friend,Al
AnswerHi Al,
There are 8 pages in the manual that show the various sensors I described and their function/replacement. I can xerox copy and mail you those. If you would care to cover my costs you could send me back three 44-cent stamps after you receive them. There is shown how to get to that temp sensor to replace it, and maybe in the course of doing that you would learn about the location of the foam. If you can't see a way to reach it, then there are a dozen specific pages (and more pages about the process of removing the HVAC unit by dismanling the dash which is a really big job) that I could copy snd send you. So let me know a postal mailing address and I will get these 8 on the way to you.
Roland
PS You are welcome.
