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?

 

Did you get a chance to check the evaporator drain located in the engine compartment on the passenger side on the firewall just below the heater hoses? If the rubber tube gets clogged with debris (leaves etc,) that falls into the cowl the moisture can't drain and gets blown around inside the cabin.

Also , there may be a problem with the HVAC system controls depending on whether they are full or semi automatic. Some systems behaved like that when a vacuum hose was cracked and leaking.

 

Thanks hanky. I think you're referring to that short 1/2 diameter outlet that comes from the box the heater core is located in? Had to change the h core out a few months back and that drain seemed to be free of debris. Also since the heater core is new I'd say that can be ruled out as causing my fog problem.

My a/c is only blowing medium cold air as well. It seems to cycle from medium cold to slightly cold, and back again about once every minute or two.

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 condenser I forget which. Said you need a special tool to remove this valve from the line. Does this sound familiar?

 

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.

 

Please,,,,,,,,,,,,,before contemplating any work on an A/C system, read ,watch and learn as much as you can.
The following may help you and maybe not,
Always wear safety glasses when working with refrigerant !
IF,,, the system is low on refrigerant,you should hear the compressor clutch cycling, (Turning on and off ). The lower the charge , the more the frequency of on and off cycles .
If low enough the compressor clutch will not come on at all.
If refrigerant gets on your skin , it can cause freeze type burns.
What might help, with the system calling for max cooling inside the vehicle and the engine running, , you should be able to feel the Accumulator ( The large can connected to the piping) starting to get cold. If it does not and the system is cycling it could be low on refrigerant. Otherwise if it is not low , adding more refrigerant than what is required will prevent it from cooling properly. I hesitate from describing adding refrigerant because there is too much chance of getting injured if not done properly.
The system has to be calling for cooling, engine running and gauges connected properly before it will allow refrigerant to go into the system. You just can't open the can and connect it and let the refrigerant go into the system,There has to be a pressure difference where the system will allow the pressure in the can to be higher than the pressure in the system. Different size fittings are supposed to prevent attempting to add refrigerant to the high pressure side where the can can explode , and it is not hard to do.
I would suggest if you can , have someone that is experienced do this for you.

 

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?

 

You are wearing eye protection ,,,right?

The blue gauge/hose is the low side AND the only way you should consider adding refrigerant.
You need to be able to control the 134 coming out of the container, there should be a valve on the container or you will need to install one.With the engine running and the vehicle calling for cooling.
Make sure both valves on the gauge set are tightly closed. Keeping the can in an upright position, the refrigerant should go into the middle hose and the valve for the low side (Blue) is opened slightly to allow the refrigerant to enter. You will notice the reading on the low side attempt to go down and as the clutch disengages the reading will go up. again. Each time it goes down it will take in more refrigerant.You should notice the cycling will get less.When the low side pressure gets near 30# it should cycle around one or two times a minute, depending on ambient temp. You should also notice the accumulator should be starting to get cold. If you add too much it will not cool as it should. For now, I would stop there, close all the vales and observe the system operation. If you close the valve on the can and the valve on the low side when the pressure is lowest,that will prevent some refrigerant from going into the air when you remove the hoses.

 

Yes thank you the eye protection is def on.

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?