Ford 8700 A/C Pressure switches?

[Conn]

I'm having trouble with my borrowed 8700. The air conditioner compressor is staying engaged, building up too much pressure on the high side and blowing lines around 200+ PSI.

I can't find any pressure switches in parts diagrams or on the tractor.

The only things I see that cycle the compressor are a temperature disc on the condenser that cuts the compressor off at 200 degrees, and the "thermostat" in the cab.


Does this sound right? I've never worked on an AC system from this era (79ish)

Thanks for any help.

 

[CCWKen]

What refrigerant are you using? Has it been converted from R-12 to R-134a? It's not uncommon for the high side to be over 200psi. Especially on hot days. It could be that you simply have bad hoses.

Most of these systems will use an expansion valve to regulate flow through the evaporator. These can stick if the system was open and/or not used for a while or someone put a sealer in the system.

What's the history of the system?
What was the low side and high side pressures at 1500rpm?

 

[Conn]

Its been converter to R134A and I've been adding a few oz of Ester oil to each charge.

The AC hasn't been used on it in probably 12-18 months. It threw the belt on the compressor and no one bothered to figure out why. (wrong belt)

Pressures at 1500 RPM on the high side are around 215PSI, and abour 30-35ish on the low side (if i recall correctly) I don't turn the switch on for very long in fear of blowing the hose again. I've already spent $100 or better on refridgerant trying to diagnose this thing. Hahahah.

The thing cools great if you can keep it from blowing lines. The high side line generally pops above 200PSI. The compressor never cycles off-on. It's just staying on all the time. Even on cooler days.

 

[CCWKen]

The low side sounds good so there's no restriction. The high side can go as high as ~285 in hot weather but should run 150-200 in mild-warm temperatures. The cab temp switch controls the compressor clutch. It should have a capillary that runs to the evaporator. If the clutch doesn't shut off, the switch is bad or maybe the capillary is covered in crud. That part of the evap may be dirty/clogged too. If it's blowing cold air, the switch isn't sensing it. I don't know why they don't (didn't) put high pressure cut out switches in these units. Or at least a compressor pop-off valve. They're required now but I guess they were trying to save a buck.

The TXV should be good or you wouldn't be getting cold air.

Make sure to use crimped hoses--Never, Never, Ever use hose clamps.

Sounds like you know some A/C but I have to ask: Did you evacuate the system before charging?

 

[Conn]

The low side sounds good so there's no restriction. The high side can go as high as ~285 in hot weather but should run 150-200 in mild-warm temperatures. The cab temp switch controls the compressor clutch. It should have a capillary that runs to the evaporator. If the clutch doesn't shut off, the switch is bad or maybe the capillary is covered in crud. That part of the evap may be dirty/clogged too. If it's blowing cold air, the switch isn't sensing it. I don't know why they don't (didn't) put high pressure cut out switches in these units. Or at least a compressor pop-off valve. They're required now but I guess they were trying to save a buck.

The TXV should be good or you wouldn't be getting cold air.

Make sure to use crimped hoses--Never, Never, Ever use hose clamps.

Sounds like you know some A/C but I have to ask: Did you evacuate the system before charging?

I'm guessing the thermostat/switch is bad. I dug around and found the capillary tube. It seems to be clean, but is floating around in a compartment different from the evaporator, so that may be the problem too.

One hose already had hose clamps on it before I started, so I just left them on there. It needs to be replaced.

I temporarily installed a variable pulse-pause timer on it yesterday. Compressor stays on for 5 seconds, and off for 7. Seems to be holding up as I moved hay with it for 2 hours yesterday and stayed as cool as a cucumber.

No. I didn't evacuate the system. (unless you count the 4x the hoses blew)

I'm in the middle of nowhere and don't have the pump to pull it down.