I have a 97 F-150 that the A/C went from blowing cold to hot instantly. I have done the following;
1. Checked fuse. Was good.
2. Checked Low Pressure connection.
On this, I jumpered the connector and could not get the clutch to engage. I also checked to make sure I had 12v from that point, which I did.
3. Checked the power to the clutch assembly. Got nothing. I also put 12v directly to the clutch and it poped in just fine.
Based on all of this I think I have a bad relay between the low pressure sensor and the clutch assembly. The only problem is I cant find it. If anyone knows where this relay is located I sure would appreciate the help.

 

Hi Gator and welcome to the forum
Your truck doesn't use a relay for the a/c clutch.
You have a low pressure cycling switch which I assume is the one you jumped. It is on the accumulator.
There is also a high pressure cutout switch on the high pressure line. It looks pretty much like the low pressure cycling switch. I would try jumping that and see what happens.

 

Thanks for the welcome Racer.

If there is not a relay on the 97 I guess thats why I couldn't find the darn thing. I did jump the low pressure switch and got nothing. (BTW-I am extremly happy that the clutch and compressor seem to be fine) What it comes down to is that I am getting no power to the clutch assembly at all. Do you think replacing the low pressure switch may do the trick?

 

Check continunity across the low pressure switch. If it's goood there will be continunity.

 

Power goes from the function switch on the dash, through the high pressure switch, then through the low pressure switch and to the clutch. Both switches have to be good.

 

I am getting power from the function switch all the way to the low pressure switch, but nothing from there to the clutch. I'm thinking I just need to change out the low pressure sensor/switch and see what happens.

 

It was the Low Pressure Switch ($18). Thanks to all for the info!!

 

OK, I have been reading for about 4 hours as to why the AC Clutch was not kicking in, did the usual checks described above, and findlay added a little R134a to the low pressure side and just as I added a very little amount, with the AC dash and key on, I heard the clutch click...
So... I cut the can off and disconnected the hose, and cranked the engine...
Well the clutch was smoking when engaged, and not turning... I cut the engine...

Does that mean my compressor is bad and locked up?

Bought the truck a year ago, it had been sitting since 2008... and the wire to the compressor was unhooked... No telling how long since it had a working AC...
Any input would be helpful...

 

I know this is an old post but I was wondering what wires do you mean that connect from the functioning switch what color are they