AC compressor wiring question


themoneypit

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I have what used to be a 1998 4 cylinder Ranger. Early in 2018, I finished swapping in a 5.0/trans from a 1997 non-PATS 2wd Explorer. The swap was very straightforward, and all things were working like factory at the time APART from the AC. I left that for later. In the past week, I reinstalled all AC components and wired up an AC compressor switch. One the 4 banger Rangers, the AC system is ECU controlled, but on the 5.0 Explorers the ECU plays no part. Since I swapped in the Explorer computer with the engine, the Ranger AC system was essentially inoperable. I've since wired the AC compressor in line with both the high and low pressure switches to a simple on/off toggle. From my understanding, this should work just fine. I tested all of the AC switches, and they worked as you would imagine. When pressure in the lines is too low (like when all the refrigerant has leaked out), the low pressure switch cuts the circuit. This is a normally-open circuit until refrigerant pressure is present. The high pressure switch is the opposite. It is a normally-closed circuit switch until the pressure in the lines gets too high. Then it trips, opens the circuit, and the compressor stops.

The wiring works, and the compressor worked great during testing while I had the low pressure switch bypassed. After recharging the system and reconnecting the low pressure switch as normal, the compressor was allowed to kick on as expected. The issue now however is that the compressor builds very little pressure at all and begins cycling on and off repeatedly. It's an endless cycle of 2 seconds of charged AC clutch, then 2 seconds open circuit, and repeat.

I have to assume that this is a faulty high pressure AC switch, but it's possible my very basic AC compressor circuit is flawed somehow. Any suggestions before I buy another high pressure switch?
 


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themoneypit

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On 2nd thought, it could just be the usual low line pressure causing AC compressor cycling. I wrote that off initially since I had just paid a shop to recharge the system, but who knows. Worth checking after work I suppose. If it turns out to be that, then I guess I'll snag a can of off the shelf refrigerant and try to top it up. And never go to that shop again.
 

Ranger850

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I think you figured it out, I'm no expert though
 

themoneypit

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Yeah, I'm betting on occam's razor here. The simplest and most likely scenario is just low refrigerant. AC compressor wiring is pretty darn simple, and all of the components worked flawlessly in the vehicles they came from.

Not gonna be too hard on the shop I guess. They seemed pretty scared as soon as I told them about the engine swap, and showed them the dash toggle for the AC compressor.
 

Bird76Mojo

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Just a thought here, but if you buy a can of refrigerant with the built in pressure gauge, then that might tell you if your refrigerant charge is too low before doing any other work to the system or buying any other parts..
 

themoneypit

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Turned out to be exactly as I feared. Found a pretty blatant leak in the AC condenser. Green refrigerant oil absolutely everywhere. Replaced the condenser this evening, and I guess I get to yell at the shop tomorrow. I'm willing to pay for the refrigerant for recharge 2.0, but I'm sure not paying for labor again.
 

themoneypit

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I'll have to cover the cost of the refrigerant, but the shop is going to cover the second evac and recharge. Fair enough outcome as far as I'm concerned.
 


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