Model: towncar limo
Engine Size: 4.6
Refrigerant Type: 134
Ambient Temp: 80
Pressure Low: 50
Pressure High: 225
Here's the deal. When I first start this car, all is well. The AC in front & in the back is blasting cold air everywhere.However, about an hour or so after driving the front air begins to lose blower volume (like turning it down to low) and then the rear follows right behind. I can put my hand over the dash vent & feel cold air but very little comes out. Same in the rear. If I close all the vents but one I can feel a very small amount of cold air. Since the back AC is aftermarket by the limo designer and doing the same as the front AC I know it's not the blend door. When I park the car and shut it off, in a few minutes a lot of water comes out of the evaporator drain in front and also out of the rear evap drain. So I opened the hood to see if I could spot any thing odd. Amazingly, the accumulator and the attached lines going to and coming out of it are FROZEN OVER with solid white frost! After sitting for about 20 minutes, I start it up and everything is back to blowing again. So I'm assuming the evaporators are freezing up and then the lines freeze up and then it stops. I tried a test while going down the road today. Everything began to shut down so I switched the front AC to the vent only setting and turned off the rear AC. As I suspected, freezing cold air came out of the vents for at least 15 minutes and the blower volume increased with each minute passed. After about 20 minutes the vent temperture began to warm up to the outside air temp. Then I turned the AC back on and all was good again for about an hour and then it froze up again. I have serviced the system with evac/recover/vacuum/recharge and all tests indicate no leaks or issues. Any ideas?? Thanks
You are goin to have to find out the pressure the system is cycling at..I suspect the cycling switch is bad, and on the highway it is dropping below the usual 21 psi they are set at. Simple and cheap enough to just change the cyling switch.. Make sure some mechanic didn't by-pass the cycling switch...Seen that before... As far as the accumulator frosting over, it will do that on a humid day, less on a less humid day.. Should be dripping water on humid days though..
Freedoms just another word for nothing left to lose
With these limo/motorhome/truck custom installations, must be classified as to the kind of control circuits they are using as they don't give out any information. With my 82 Pace Arrow, I called their tech service and they told me the AC system was strictly Chevy, dealer was no help, but let me look at some very old shop manuals, still couldn't find anything on the climate control panel, practically all have mating connectors, this one while looking like GM has 19 spade terminals on it with individual wires that the previous owner really screwed up. So had to take it apart and make my own circuit diagram tracing out all the wiring to see where it went. With a drawing of the rest of the system components.
So the first question is, did your freeze up problem just start, or was it always that way? Are you using an expansion valve system or a FOT?
You got to know what you have before playing with it, did you try contacting the limo company? Somebody put this system in, think they hired some guy off the street and never got his name, because nobody left there seems to know nothing. Chris142 is having the same problem with trucks.
This looks like it'd be about the same as an American factory dual air setup -- stock CCOT system front with rear evaporator added in parallel with a TXV on it. If there's a two-wire cycling switch, unplug it and the compressor should disengage, showing the car's wiring is in order. Then it pretty much has to be the switch iteslf. It is very simple to replace, can be done with the refrigerant still charged.
Make sure that it isnt a case like my 1985 Caprice where there is an adjustable cycling switch. This car did the same thing and nobody could figure it out until the A/C guy removed the connector from the accumulater. He found the screw which is inside the connector, adjusted it by trial and error and all is well. Says he never saw that before. My Bonneville doesnt have such an adjustment never mind its the same system.
2008 Chevrolet Impala LS
1981 Pontiac Bonneville
2007 Sears Craftsman Lawn Tractor
1985 Chevrolet Caprice
1986 John Deere 165 lawn tractor
Hello again: OK I just installed a new cycling switch. When I unhooked the old one with the motor running the compressor shut off so the wiring is normal. However, as I loosened the old switch a bit of pressure came out of the threads and it was covered inside with A/C oil. Is this normal??? I'll test drive the car tomorrow and see if my problem is fixed and then I'll post again.
Yes this is normal, there will be a tiny amount of refrigerant and oil trapped in the old switch. Not enough to worry about. You should check for leaks at the new switch to make sure you got a good seal with the o-ring.
Hello again. I installed a new cycling switch and all appears well. I'm going to take a 2 hour trip this weekend so I'll post back the results. Thanks to everyone who gave me advice.
Good news!!! I'm freezing again! Took that trip and the AC was great and never stopped working. Thanks to every one who chimed in. Hard to believe that little part was the problem. What a great forum for guys like me. I know where to buy my parts now too.
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