How does the AC system work in early OBS models?

[PlayingWithTBI]

You might wanna double check the HP switch if you go this route. If it doesn't close until 200psi, your compressor clutch will not engage because your high side static pressure will equal roughly the ambient temp when the ac is off.

FWIU - it opens when it reaches 400 then closes again when it drops below 200 (hysteresis). I checked it before installing it and it is closed. After installing the new NAPA compressor, HP switch, orifice tube, and evacuating it for 45 minutes it's running about 40psi low side, 300 on the high side at idle (with ambient temp ~110). It goes down when revving it up to ~1800rpm so, it looks good so far. I'll wire in the switches maybe tomorrow.

 

[Jglew82]

FWIU - it opens when it reaches 400 then closes again when it drops below 200 (hysteresis). I checked it before installing it and it is closed. After installing the new NAPA compressor, HP switch, orifice tube, and evacuating it for 45 minutes it's running about 40psi low side, 300 on the high side at idle (with ambient temp ~110). It goes down when revving it up to ~1800rpm so, it looks good so far. I'll wire in the switches maybe tomorrow.

Awesome, then that should work well. Sounds like you might be able to use just a tad more 134a as well with those pressures and temp, but you can judge by feel once you get rolling. Easier to add than subtract!

 

[PlayingWithTBI]

Awesome, then that should work well. Sounds like you might be able to use just a tad more 134a as well with those pressures and temp

Thanks, I stopped adding when the compressor started making noise. May add one of those little cans with 3 oz 150 PAG and 134a to top it off.

 

[wb292]

Does this switch also control the condenser fan?

 

[PlayingWithTBI]

Does this switch also control the condenser fan?

Unfortunately there's no condenser fan on my 88 so I can't help you there.

 

[GoToGuy]

Best practice would be leaving it the way GM engineered it. Pressure cycle switch to control normal operation. Over pressure switch to prevent catastrophic actions. 400 plus blowout and your standing next to it would make a very exciting day.

 

[PlayingWithTBI]

Pressure cycle switch to control normal operation. Over pressure switch to prevent catastrophic actions.

The only problem was the earlier GMT400 R12 A/C systems didn't come with a high pressure shutoff switch. The discontinued (by GM) one-wire switch that came with them just opened the fresh air door to help lower pressures. Originally the compressors came with a blow off valve which, when it blew to atmosphere (R12 to atmosphere hmm), you had to go back to the dealer and get a recharge. A big mistake by GM, especially in a hot climate like AZ.

I had that switch blow out of the back of the compressor because the replacement R4 compressor didn't have that valve, sounded like a shotgun going off. Mine works just fine with the factory spec 200/450 PSI switch, been working fine for 2 years and going.

Trust me, I've done a lot of research on this

Here's how I wired it along with a relay giving full battery voltage to the clutch since my 88 only supplied ~11.7V from the CC. Notations in blue are upgraded components.

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[GoToGuy]

My brother in law thought he would add just a little more 134 and bang, all gone.

 

[PlayingWithTBI]

My brother in law thought he would add just a little more 134 and bang, all gone.

What model year was that?

 

[GoToGuy]

He got a new compresser and kit for 134 conversion. I said I'll be over to help but no Mr can't effing wait 10 mins pressed on and new compresser toast. His early 90s suburban.