A/C Switch question
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A/C Switch question
The '79 F150 that I bought recently has factory air with the Hi/Lo feature, etc. I discovered a toggle switch had been installed on the dash just under and to the left of the steering wheel; thought it was for some fog lights that were installed. To my surprise, the previous owner rigged up the a/c compressor to this switch. Obviously, the factory switch doesn't turn on the compressor when it is slid to its position. I would like to eliminate the toggle switch and get it back to "normal". What will I most likely find when I tear into the dash? By the way, all of the other features work with the switch and air is diverted to the areas that they should respective of the position of the switch. I assume the switch failed and that is why the previous owner rigged up the toggle switch. Any help would be greatly appreciated.
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The previous owner probably rigged up the toggle switch to by-pass a failed high or low pressure sensor in the a/c system.Before you tear the dash apart, check under the hood for the a/c compressor. Trace the black wire connected at the a/c clutch and see if it has been tied into. There probably has been a splice through a hot lead into the toggle and back to the a/c clutch.
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You will need to figure out if the by-passed sensor that has gone bad is a high or a low pressure sensor. If you are not familiar with auto a/c systems you will need to find some one is. The repair of this involves opening up the refrigerant lines.And since you can no longer get R-12 freon( at least not cheaply) possibly a conversion to R-134a.
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Good advice. Do you know where I can find a wiring diagram of this particular area? Where should the wire running from the compressor go? I have to sign off for now, but will check in later tonight. Thanks for your help.
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I'm guilty of doing the same thing. It was a temp. fix to get A/C working until I could get a new switch. I got the whole dash switch assembly at a junk yard for $25. Plugged it all in, put the wire back to the factory wire...worked no prblem..took a hour max. Its a little tricky getting all the vacuum, and other linkage just right, but not to bad...and I'm no mechanic!!
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It will be a wire that runs along the side of the valve cover to the front of the compressor.
It is a flat slide-on connector as they usually fail because they get too hot and burn/melt the connector.
I can supply some diagrams but thay aren't perfect.
One of them is already psted in another active AC related thread.
My guess is the P/O didn't want to replace the entire dash switch which usually is the problem
It is a flat slide-on connector as they usually fail because they get too hot and burn/melt the connector.
I can supply some diagrams but thay aren't perfect.
One of them is already psted in another active AC related thread.
My guess is the P/O didn't want to replace the entire dash switch which usually is the problem
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Any diagrams that you could provide would be greatly appreciated. My guess is that the original wire you described running along side the valve cover has been removed. I may have to rewire that section. If you would, please supply me with the diagrams you have, or point me to the active thread you referenced. Thanks a mil1ion!!
Fleet Owner
Joined: Jan 2004
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From: Brentwood,CA
the factory setup does not use a HI low switch in the ac line. it uses a frost switch mounted inside the cover of the plenium. its a silver box with a green , brown and black wire in it.these do go bad .
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Here's the other active thread.
https://www.ford-trucks.com/forums/s...d.php?t=465047
Here's the underhood look.
https://www.ford-trucks.com/forums/s...d.php?t=465047
Here's the underhood look.
More Turbo
Joined: Mar 2002
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From: Colstrip, MT
It's possible that the only thing wrong is the electrical connection of the brass contact on the vacuum switch. The contact acts like a spring. When the slide switch is moved to the A/C position, the spring contact is supposed to "fall" into place. I had the same toggle switch. Replacing the vacuum switch on the heater A/C panel with a NOS one from e-bay solved the problem. Cost was about $30 for the switch and about 2 hours of my time.
Cargo Master
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Originally Posted by farmnaggie
Thank you for that bit of info, ford390gashog. Help me out with the location of the plenium. I'm not sure I know where you are talking about. Thanks!