Hello,

I'm new to the forum. I have a 1990 F150. The AC compressor won't kick on at all. I want to see if I can jumper the low pressure switch to see if the compressor will work. Does anyone know exactly where it would be located and what it looks like?

Thanks!

 

The LPS is screwed onto the side of the accumulator. That's the "AC can" near the firewall on the passenger side. It is the only thing with wires attached on the accumulator.
It looks exactly like a low pressure switch screwed onto the side of the accumulator.
Sorry, I had to say it. I don't have a pic.

You should find it very easily now that you know where to look. A paper clip works nicely to jumper the switch CONNECTOR. (I've told folks to jumper the cycling switch and they have jumpered the switch contacts). Don't run it for more than about 1 minute or so at idle or you could damage the compressor.

If the compressor runs with the LPS connector jumpered, feel the pipes on the accumulator. If they start getting cold, the switch is faulty. If they stay warm, the system is probably empty of refrigerant.

Post back with the results.

Edit: If the switch happens to be bad and the system is full of refrigerant, there is a schrader valve on the switch port. You can safely remove the switch without losing the system charge.

 

Thank you for the information. I'll take a look this evening and post back.

Thanks again.

 

I have a '94 F-150 4.9L. I bought it new. It eats low freon switches. I'm probably on my 3rd one. Every few years, I'll be driving with the AC on, then the air goes warm. Jumper out the connector, blows cold. Go buy a new switch and screw it in...problem solved. For a few years anyway!

 

Ok I was able to jumper the switch and the compressor kicked right on, but it's blowing warm air.

Since it's a 1990 I guess it has R12 correct? How much would it cost if I took it to a shop to have converted to R134a?

Thanks.

 

Would you by any chance be using Wells brand switches from Auto Zone? That's about how long they last.

 

Depending on where you live, I'd say about $3-500 to have it done correctly. (system flush, new accumulator, new orifice, etc.). Beware of shops that say they can do it for ~$135. It's a down and dirty conversion and the results usually show it.
If the compressor body or shaft seal is leaking, add ~$300.

 

No, they've all been from O'Reilly's...I can't spell it...

 

Just posting here cause I have to do the same thing.

 

Hmm. A quick check of O'reilley in Mansfield, Ohio, or whatever the spelling, only shows Motorcraft switches. If that's what you're buying thet should last for many years. I can't even guess why they're failing so soon.