1989 F150 A/C freezing at Orifice tube

[mattrenegade]

Personal truck for hauling and shop use. The A/C line started to freeze up and blow hot air. Pressure side. Strange thing is.. New Evap, New Lines and orifice tube. Flushed out condensor ( stock) I know moisture causes freeze up. But system was pulled down with vacuum for an hour before charging it... Any ideas? Clogged orifice tube maybe ?

Compressor comes on all the time on this truck Even if system is empty it will come on. Only has a High Pressure switch on it. From what I can see and know. Low side is around 45 High side is 150 . Compressor is not cycling at all.... On all the time. Suction hose is warm , High side is really HOT ! Freezes after orifice tube going into evaporator. I took all the hoses off. Blew through everything with alcohol. Put it all back together and charged it a little. And it is cold at the inlet tube into the evap after the orifice tube and that is it. Frosts up as in pictures. Maybe the new compressor is not functioning correctly ? Plugged or restricted New Evaporator ? I get air and alcohol through the system when I blew it all out. Its so simple... yet something is messed up....

I will pull another vacuum on it and check the compressor. There is a Cycle switch on the dryer. That is new as well. When I bought the truck for the shop the Evaporator and all the hoses were gone. Compressor was locked up. So the compressor, Hose assembly, Evaporator , Dryer, orifice tube and switch are all new. When I first replaced all the stuff to get the system back working. It worked very well. Cooling at the vents at 45 degrees. Ran it for about an hour total after the re- install of everything. The truck sat for about a month before I used it again and the A/C was not working. Found the freezing inlet tube on the evaporator and that is where I am now. Truck is parked again and I will get to it a little later this week. Was using it and started to check on this A/C issue because shop was slow. Back to the Customer Pay stuff for a bit.

[GM Tech]

You answered your own question-- you said it never cycles- and compressor stays on even with no charge-- so that is what is wrong--make your cycling switch work so IT WILL AVOID FREEZE UP. as designed. If pump runs with no refrigerant in it- someone somewhere has bypassed the cycling switch - so find that mess and wire it back to OEM specs...It could just be a stuck relay- so try that first....

[mk378]

Unplug the cycling switch while it is running-- this should make the compressor stop. If it does not, troubleshoot the electrical problem. If it does, the switch is probably bad. Make sure the switch is screwed on all the way (hand tight only though), as it needs to be all the way on to open the shrader valve and see the pressure from inside the accumulator.

The switch is supposed to open when the low side goes below about 25 psi. Setting the interior fan on low and revving the engine should pull the low side down enough to test the switch.

[mattrenegade]

I will double check the cycling switch and wiring. The wiring does not looked hacked or messed with. I will also check the switch . Murray parts on the whole thing. All knew. So it is confusing.

[mattrenegade]

This is where this system is freezing. But.. I dont think this is causing a block. Its right at the Orifice tube Cycle switch is good. Pull wires and compressor goes off. I was looking for a High side switch on this truck and cant find one anywhere... Not even one on the compressor.

http://www.batauto.com/attachments/0916161131-jpg.9160/

[mk378]

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Have you confirmed the compressor cycles off when low side goes below 25?

Many R-12 vehicles did not have a high side switch. Those only function to cut the compressor off before a hose or something else blows out in an abnormal situation.