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Had an interesting failure today and I wanted to make sure it wasn't a fail safe thing that indicates a bigger problem before replacing the component and moving on. 

The comanche was at idle and I was working on the cooling fans. All the sudden I hear a pop and what sound like all of my refrigerant escaping. Well the pressure switch failed in a way where the refrigerant was leaking out of one of the prongs on the switch itself. Is this like a over pressure fail safe? AC was staying on steady with no apparent cycling so I do not think the system was over/under charged. 

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99% this was just a failure of the switch, not any kind of safety precaution. If there was a safety in the system, it would be in the form of a binary high/low pressure switch that disables the A/C request signal, not as an explosive decompression.

 

I've seen quite a few oil pressure sending units fail in exactly the way you describe. You should be OK with replacing the switch and recharging, but you will obviously want to watch the high side pressure as you do so. Since the refrigerant escaped so quickly, you will want to add oil as well.

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Your cooling fans keep the high side pressure from becoming excessive. If you disabled the fans at some point with the A/C on, the pressure increased but your high pressure switch failed to disable the compressor clutch, then the gas found a way out through it...

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I agree - a simple failure of the switch.  But as Zomeizter said, the switch was likely malfunctioning from the beginning and your high side pressure could very easily have exceeded a safe level.  Hopefully it didn't cause any additional damage if so.

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I do not know if the pressure switch on these trucks had a high pressure cutoff feature but I'm leaning towards no. The FSM makes no mention whatsoever of a high cutoff pressure.

 

Now for the later 94-96 systems, I've seen some literature that suggests the switch has a high cutoff at 475 psi.

 

Like I said, be careful when recharging.

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1 hour ago, Minuit said:

I do not know if the pressure switch on these trucks had a high pressure cutoff feature but I'm leaning towards no. The FSM makes no mention whatsoever of a high cutoff pressure.

 

Now for the later 94-96 systems, I've seen some literature that suggests the switch has a high cutoff at 475 psi.

 

Like I said, be careful when recharging.

 

I have a dual manifold for R134a and a vacuum pump. I will have to do some research on R134a as the last few systems I have done have been 410a (house AC and mini-split). 

 

Edit: I am not mixing 410a and 134a manifolds before anyone warns me =P

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