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Discussion Starter #1
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.


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

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How well does your ac work? Does it cut out at only wide open throttle or randomly?


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Sounds like your blend door isn't working, at least not properly. The fan working intermittently sounds more like a safety, your evaporator coil may be icing up.
 

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Discussion Starter #5
Thanks for the help and sorry it's been so long since posting this. Still having the same problem.


A/C works sort of intermittently like the defrost. It goes from medium cool air to slightly cool air, back and forth about once every minute or two. Doesn't seem to be effected by the throttle but I'll try to remember to test it out.


CatSkinner actually the fan works ok, it's the temp (a/c) that goes up and down, or the defrost that seems intermittent. But the fan, air movement, is ok.


Had a guy tell me earlier today that 70% of the time when you see a problem like mine it turns out to be what he called a valve inside the high pressure line that comes straight off the compressor, or condensor I forget which. Said you need a special tool to remove this valve from the line. Does this sound familiar?


And if my evap coil is icing over how could I test that out. I don't even know where the dang thing is. The cycling of the cool to slightly cool air and back again happens like I was saying about once every minute or two, so without knowing much about this I'd think that wouldn't be enough time for the coil to ice up and then thaw out. But that just my amateur 2 cents.
 

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The evaporator is in the dash not accesable but youll know its icing over when the ac isnt sweating as much as before and the compressor would short cycle. There is a high pressure cutoff switch on the drier (its a black cylinder on the passenger side near the firewall in the engine bay) but I doubt the switch is the culprit. At this point your best bet is to put manifold gauges on it and see where the pressure is on the low and high side.


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The evaporator is in the dash not accesable but youll know its icing over when the ac isnt sweating as much as before and the compressor would short cycle. There is a high pressure cutoff switch on the drier (its a black cylinder on the passenger side near the firewall in the engine bay) but I doubt the switch is the culprit. At this point your best bet is to put manifold gauges on it and see where the pressure is on the low and high side.
That is the low pressure switch on the receiver/drier
 

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That is the low pressure switch on the receiver/drier


Hmm Im sure youre right. Thanks for correcting that.


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Discussion Starter #9
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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Try the dye first. Any leak will then be easily detectable with ultraviolet light. The system probably has some already installed from the factory, but add some to be sure (Gauges will only indicate a leak, but not where). You can then fix the leak before losing expensive refrigerant.
 

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Discussion Starter #11
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 went between 90-140. 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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Your compressor isn't hurt. Its doing what its supposed to do. It will cycle via the low pressure switch at the receiver/drier to prevent freezing.

Make sure both gauge valves are closed. The middle yellow hose is connected to the can of refrigerant. You charge only through the blue, low pressure side. Do not open the high side or you can explode the can. Add a little at a time. If the outside temp is around 60 to 65 you'll want it to maintain a low pressure of around 30 with compressor running full time. Don't overcharge like some do thinking it will cool more. Its just the opposite. The lower the pressure the colder the temps across the evaporator.

Air on max and blower on high.

Outside temps

60° - 30psi
70° - 35psi
80° - 40psi
90° - 45psi
 

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Discussion Starter #13
Gotcha, thank you.

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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It has a schrader valve.

Oil is collected in the compressor no need to add more.

When you change the valve you will be introducing air and moisture into the system and technically should pull the system into a vacuum to remove it. Might try tightening the valve and see if it seals before changing.
 

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If you are going to replace Schrader valve cores you may need something like this ,

[ame]https://www.amazon.co.uk/Magiin-Accessories-Conditioner-Schrader-Remover/dp/B0776S45CZ[/ame]

[ame]https://www.amazon.com/MASTERCOOL-81490-R134a-Remover-Installer/dp/B000KITSMI[/ame]
 

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And if it leaks that bad, you probably ought to evacuate the system before adding refrigerant to it.
 
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