I have a 1978 F150 with Factory Air. I replaced the York with a Sanden Style Compressor, R134, new condenser, hoses last summer but kept the original evaporator and controls.


It worked well until this past month my blower motor began to howl so I bought a new blower motor, new heater core, and a new evaporator for only $11 on Ebay and it was the right part. Amazing!.

I went in from under the dash and replaced all these part and then charged the system today.


It was blowing really cold air () 35 degrees and then on my test drive of about 6 miles I noticed that the air was coming mostly out of the heater duct on the floor. Then it stopped blowing cold.


When I got home I put the gauges on and it still has R134 but the compressor was not running. Low side about 70 lbs and high side just about 20 lbs


Could it be the Deice Switch? I had to take it off to do the new evaporator install? If it fails my understanding is that the compressor stops. I found this part online AKA AC Limiting Switch. Is this the same as Deice?


Could it be the AC Damper Switch Assembly? I am asking this because of all the air coming out the heater duct. I did not touch this during the install. I found the new part for $50 online. I have read that a vacuum leak can cause the air compressor to stop as it defaults to defrost but my air was coming out of the heat duct.

I am guessing I should get a volt meter check to see if I have power to the clutch on the compressor first.


If not then it is probably one of the above switches.


There is no pressure switch on the 78 F150 that I know about.


Any help would be appreciated.