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AC Clutch Switch Adjustment?

Old 02-09-2019, 11:57 AM
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Car: 1984 Firebird S/E
Engine: 1985 2.8 MPFI
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AC Clutch Switch Adjustment?

Hey everyone,

Finally got the new system gassed up with R134a and the cycling switch isn't seeing the correct pressure, either that or its dead, despite that its new! Sounds legit.
Anyway if i jumper the connection the AC system runs fine, if i reconnect the switch it doesn't work at all. So I'm guessing either the low isn't low enough on the R12 switch the new accumulator came with, or the switch is dead and I need a new one.

But if the switch is alive which way do I turn the grub screw to lower the switch pressure?

Thanks in advance!
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Old 02-09-2019, 04:38 PM
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Re: AC Clutch Switch Adjustment?

It isn't a "cycling" switch. It's a low pressure cutoff switch. Its purpose is to protect the compressor against running with an empty system, which will prevent oil and cooled refrigerant from flowing through it, and thereby burning up the comp.

Accumulators don't generally come with switches. Might want to take the one off the old one and put it on the new one.

No AFAIK there is no adjustment.

The switch should allow the comp to run as long as there is any pressure in the system above 25 psi or so. It will shut off when it goes below that.The pressure in the system should go to the vapor pressure of the refrigerant, on both sides, when the system is not running. Should be anywhere from 60 some psi @ 5C up to 100 psi @ 35C. (not that you're ever likely to reach that...) The pressure on the high side should increase to 200 some odd psi once it starts running, and decrease on the low side. Under normal conditions - let's say 28C ambient - the low side should go down to 35 or 40 psi. If there's not enough cold juice in it, the low side pressure will go too low, and it will shut off.

It's also not impossible that your switch isn't screwed on far enough, and hasn't reached the point of opening the Schrader valve to expose it to the inside of the system.
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