AC Pressure Switch

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565bbchevy

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Aug 8, 2011
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Is there a GM pressure switch that will fit my 86' Regal that is compatible with 134A and uses the same 2 prong harness?
Maybe off of a later model vehicle.

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melloelky

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can i ask what difference that'll make? i only ask because i tried the 134 and it didn't work so i settled for the r12 version.
 

69hurstolds

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You can always buy one...

But most pressure switches have a screw between the blades that you can adjust the pressure. 1/4 turn is about 4 psi. After conversion to 134, you're supposed to lower it to get around 20-21 psi to cut the compressor on. Counter clockwise lowers the cut in pressure. Watch your low pressure side to see where the compressor cuts off and adjust accordingly. Obviously, be careful with this.

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I'm betting those "conversion" switches are just re-adjusted R12 switches. I don't know though.
 
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melloelky

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hmm,i tried adjusting mine as the compressor doesn't cycle on/off but runs the whole time the a/c's on.it's shuts off when selected to do so.maybe the swich is bad i don't know.
 

69hurstolds

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hmm,i tried adjusting mine as the compressor doesn't cycle on/off but runs the whole time the a/c's on.it's shuts off when selected to do so.maybe the swich is bad i don't know.
It's easier to do when you're charging the system and it's kind of low, and the compressor cycles. Kind of a PITA if the pressure stays high enough to keep going. Easier to do on colder days. Summertime probably ain't it.

Sometimes it's tricky.
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melloelky

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fair enough reverend run..i did it the first time i charged the new system actually i didn't know where to start and i put two lbs in it and it wasn't twisting the needle off so i left it.
 
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69hurstolds

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If it's working fine, you should be ok. I also know quite a few people that do the 134 conversion and don't change the accumulator (R12 ones have wrong desiccant, get a 1993 one if possible) or mess with the cycling switch and GM even said you can leave the mineral oil in the system. I disagree. I guess technically you could, since it doesn't mix with 134, but if it ever slugs out on you...Get as much mineral oil out as possible. But I digress.
 

69hurstolds

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I just thought of this...if you are daring....if you back off the screw in the switch 1/4 of a turn CCW, that lowers the pressure approx. 4 psi. Since the R12 switches are normally factory set to 25 psi, that 1/4 turn should get you right around 21 psi where you need to be.

Just an idea. I make any and all disclaimers of knowing nothing or seeing nothing.

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melloelky

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I'm not worried about,i only spoke up originally because 565 asked about the switch and when i tried the 134 switch way back it wouldn't thread into the new accumulator so i exchanged it for the r12 version.still it wouldn't adjust.the evap core hoses,condenser,compressor everything's new and it's fine.i think with the heat index we've had as of late i don't think the pressure's on the low side rite now anyways @60 degrees inside the cab and 95 outside the car.
a/c can never be cold enough imho
 
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