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Compressor cycling, but not a freon issue

Ed_of_Texas on Tue September 13, 2011 7:29 PM User is offline

Year: 2007
Make: Lincoln
Model: MKZ
Refrigerant Type: R134
Ambient Temp: 100
Pressure Low: 50
Pressure High: 220
Country of Origin: United States

I have already been through the obvious steps: had it evacuated and recharged to a proper charge, had the dealer look for leaks, etc. So I am fairly certain that it is not under or overcharged and that all of the major ac components are fine. But it is only cooling down to about 74 degrees in the car (with an outside temperature of 103). The temperature coming out of the vents is about 52. Even though I realize we're in hot weather, I still believe that it should be getting cooler than that. And, most significantly, the compressor is cycling about every 20 seconds. I have talked with several car folks I trust and the concensus is that something (besides freon charge) is causing the compressor to kick off and on and it is simply not staying on long enough to cool the car adequately. But what could be causing the cycling? Is there a sensor or switch that could be bad? Apparently, this car does have an "Ambient Air Temperature Sensor" in the evaporator, but I can't find out what it does. I would sure like to know with 99% certainty if that could actually be the problem before I dismantle the dashboard. I hope one of you has experience with this. Thanks. (Note: this car cross-references with the Mercury Milan and, I think, the ford Fusion, if that helps).

tvlunn on Wed September 14, 2011 6:01 AM User is offline

Can't be sure of your exact issue, but read the following post ....................... go to the last post if you don't care to read all of the other comments:

Edited: Wed September 14, 2011 at 6:02 AM by tvlunn

bohica2xo on Wed September 14, 2011 11:16 AM User is offline

That vehicle has an EATC panel. There are useful built in diagnostics available.

The EATC panel is capable of testing all three of the temperature sensors in the system from the driver's seat. No need to tear out the dash to test a sensor.

The EATC is also sensitive to battery voltage. It even has a code for this. Check the vehicle battery voltage before starting the engine in the morning with a voltmeter right at the battery. Check it again after starting the engine. Post those voltages here.

I would recommend a subscription to Mitchell for that vehicle. It covers the steps to retrieve the codes via the A/C display, and gives detailed info on the codes. It will also show you how to get to the sensors if one is actually bad. There is so much complicated stuff on vehicles like that you really need the full manual like the dealership has. Mitchell does a nice job of presenting it.


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