AC freezing up

I had a 92 WS. It had the trinary switch. I think it’s a low pressure, high pressure, for air compressor, and another high pressure for fan. 3 switches in one. My Freightliner has a binary, high/ low for compressor, and separate fan high pressure switch. I’m thinking if you run 3 jumpers. Establish which one turns compressor on, that’s the low pressure switch. Then after it’s been running a while, see which one turns the fan on that’s the fan high pressure switch. Last one is compressor high pressure switch. Just guessing honestly. It’s been a long time 22 yrs since I had my WS. Learned on that Truck. The power switch to compressor is a cheater switch. Very common in the older Trucks. Lot of Guys would do that, instead of fixing it right. Need to eliminate it, or keep it for an emergency, I guess for anytime the low pressure switch goes bad. Hope I’m not sending you on the wrong direction. I don’t really know how to diagnose the circuits. Just test them with a light, and guess, any more is a mystery. Lol.

 

I’m looking at my book. Says you should have one of these trinary switches. # 11-2625, it has a 1/4” male thread, it’s Normally open. it shows open at 22-325 lbs. and closes at 40-230 lbs. Or # 2627, it has a 1/4” female thread, it’s normally closed. It shows opening at 22-325 and closes at 40-230 lbs. Both operate at same pressures. Normally Open # 2625 disallows current within the pressure settings, Normally closed # 2627 allows current flow within pressure settings. I don’t know which side the fan operates from, or if it operates on from one and off from the other. No idea. I can’t recall if my compressor cycled off and fan went on at the same time. Seems like fan would be the 230 setting, then compressor would shut off at 325. That way fan would come on first. Need to trace that added dash switch, find the power source, probably from the solenoid on firewall, and then it’s spliced into the compressor power wire. Disconnect it. Start from scratch jumping wires from plug to trinary switch. All vague ideas. Hope it helps.

 

Is this a 379 Pete? I was assuming it was. Peterbilt ran grounds to activate relays, not power.

So you'd have a ground to thermostatic switch, then to trinary, then through firewall connection to relay. Newer trucks would be the same substituting a high and low pressure switch.

The relay once grounded sends power to A/C clutch

 

Your thinking about Kenworth. Peterbilt uses power to activate the relays.

 

Probably a short somewhere. That’s why they wired the extra switch. Between the compressor switch and fan switch, you could just about run without the trinary switch. Just have to leave Freon a little low, and manually turn fan on when stopped. A friend of mines doing that now, on his Freightliner. Someone took the fan switch off, it’s missing, don’t know why yet, he’s going to get a new switch. Meanwhile we left the Freon a little bit low. Compressor runs almost constantly. Hardly ever cycles off at all. It’s blowing ice cold, since it’s running all the time. He just turns fan on manually while idling for any amount of time. Every stop light. I’ve done that when my hi/Lo binary pressure switch is bad. Jump the pigtail, and run it low on Freon, so it doesn’t get too high and blow a hose. Shortens the life of Compressor, since it will run hotter, when low on Freon. Freon cools the compressor. Low Freon will shorten the life more than low oil will. As long as it’s not too hot to touch, it won’t really hurt it being a little low. I’m guessing that’s what they were doing when they added the switch. Putting just enough freon to make compressor run all the time, and cool the cab.