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Have a '11 Crown Vic with 290k miles and I've been having a problem with the windows fogging up all the way around. The defrost seems to be working about half the time. On humid rainy days it'll work for say a half hour keeping the windows clear, then the windows will fog hard for 10-15 mins. And then it might decide to start working again, back and forth it goes. When I started it just now the compressor clutch turns when the a/c is turned on, although I haven't had a chance to observe it when the windows are fogging.


A secondary problem it has is that it only blows air through the vents on the front of the dash, straight out into the cabin. The air flows only very weak out the defrost vent at the windshield or the floor. It does this on all settings. Although this might contribute somewhat to the problem, it seems like the a/c does completely cut out as the windows will still fog hard with the a/c set to on and on full fan. When it cuts off the air in the cabin feels immediately humid. One that that helps somewhat is to turn the temp toward cooler and it seems to not fog as much and gives it a chance to maybe clear the fog some.

I'm sure it's not my heater core leaking as I just had to replace it a few months back.

Any idea what's causing this or what I should do to start testing?

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I gotta say, I think it is time for a replacement for her....looking at the forum in which you have posted, you are having all sorts of issues with a car with a lot of miles on it...maybe it is time for a trade in.

Edited by twintornados

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You gotta get the HVAC doors working correctly, and achieve correct flow first. This still uses vacuum to control the mode doors. Defrost on, outside air door open is the default (no vacuum) setting, so either the door(s) are binding or something is going on in the control. THEN worry about what the AC clutch is or is not doing. 

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I'm gonna assume my problem is being caused by low refrigerant and take a shot at fixing it as cheaply as I can.  But at the same time I'd like to take steps at identifying where the leak might be.

So what will this look like?  Renting some gauges from the local car store and checking my refrigerant lines?  How would you go about this and what readings should I be looking for?

And then if things read low I would get a can of refrigerant with leak revealing dye and put it in the system?

Sorry I'm so remedial here, first time working on an a/c system.

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Please see my above post.   Addition...I agree I'd like to get the air flowing correctly first but I've got both a time and budget crunch and I believe if I can get my a/c fogging / luke cool air problem fixed everything will work well enough.

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Hooked the gauges up and it seems like I've got a low refrigerant condition.  Before turning the engine on both gauges read about 75.  After starting the engine and setting the AC on max you could really tell the compressor was cycling fast.  The needles cycled every 5-6 seconds...one going up and the other down, then reversed.  The blue gauge cycled between 22 and 38 PSI while the red cycled between 90-140 PSI.  The outside temp was about 60 F.

From what I've read, especially with the compressor cycling so fast, this indicates low refrigerant.  Hopefully my compressor isn't hurt by running it for so long like this.

How do I go about using this 2 gauge setup to add refrigerant?  Should I add it through the middle hose somehow or get a can of 134 with a gauge on it and just add it directly from the can? 

And how do you know how much to put in?

 

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Dude. Fixing the AC wont do dick if you can't control the air doors correctly. A/C working or not, you can't defog without proper airflow. You say you want to fix it cheap, but are still putting money into the A/C.  

Not using an AC machine, I would slowly add through the low side with one of those aftermarket fillers so as to NOT flood the compressor with liquid. Ambient temp, underhood temp  and moisture in the air play a role in calculating pressures. WARM ENGINE, FAN ON HIGH, RECIRC DOOR OPEN at 60 degrees F, I would probably expect your high side pressure to be stable in the 150 psi range, with the low in the  very low 30s. I might expect some cycling, but not much. Altering temps will alter those readings. 

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OK thanks YT I got it.

After I took the gauges off I noticed one of the schrader valves was hissing, and now the system is down to 0 psi.  So I believe a faulty valve has been the culprit all along.

Now that the system is down I'm going to replace both valves, but my regular schrader valve removal tool won't fit down on the valve.  The stem of the valve is too long and the tool won't go down around it to twist it out.  I need a tool with prongs longer to fit down into the recessed sides of the valve.  Does this '11 Crown Vic have schrader valves or a different kind of valve?

Also, when I go to fill the system with refrigerant, do I need to add any PEG oil or just add refrigerant up to the specified capacity?

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How about not posting the same problem in three different threads....

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I can't remember what it has for sure. Some of the ENDS (where the cap screws on) are replaceable and that is the only way to service the valves. They usually will have flats that you can put a wrench on. Some of them have larger valves than the typical tire type, for which you need a different tool. You might need to add a couple ounces of PAG oil, but I'd do so sparingly. 

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