How does the AC system work in early OBS models?

[Donald Mitchell]

Do you know what High press switch you used? What year? I'm going to try this if i can find the right part.

 

[PlayingWithTBI]

Do you know what High press switch you used? What year? I'm going to try this if i can find the right part.

This one, it even comes with the connector

https://www.oreillyauto.com/detail/c/murray-climate-control/engine-sensors---emissions/body-switches/a-c-pressure-switch/d70a70727ba7/murray-climate-control-2-terminal-pressure-switch/mry0/35961/v/a/3009/automotive-truck-1988-chevrolet-c1500-pickup-rwd?q=a%2Fc+pressure+switch&pos=0

www.oreillyauto.com/detail/c/murray-climate-control/engine-sensors---emissions/body-switches/a-c-pressure-switch/d70a70727ba7/murray-climate-control-2-terminal-pressure-switch/mry0/35961/v/a/3009/automotive-truck-1988-chevrolet-c1500-pickup-rwd?q=a%2Fc+pressure+switch&pos=0

 

[Donald Mitchell]

Thank you!

 

[Donald Mitchell]

"I'm thinking of hooking the HP switch in series with the LP switch and shorting out the HP connector." If I,m correct you grounded the single wire form the old pressure switch?

 

[PlayingWithTBI]

If I,m correct you grounded the single wire form the old pressure switch?

Yes, I grounded it to the T-Stat bolt.

 

[Schurkey]

The old, one-wire switch would be easily replaced with a two-wire switch, provided the "trip" pressures are the same for both switches.

A one-wire switch grounds through it's metal body, where it contacts the aluminum housing of the compressor.

Given that the switch is sealed with an O-ring, and the wet side of the O-ring is going to be bathed in refrigerant oil, using the switch body is something of a dodgy grounding scheme.

OTOH, with a 2-wire switch, when the contacts close, the second wire, tied directly to a good ground with a low-resistance wire, has no problem conducting current.

So the 2-wire switch is nothin' to be scared of, IF (big IF) the switches trigger at the same pressure.

 

[PlayingWithTBI]

The old, one-wire switch would be easily replaced with a two-wire switch, provided the "trip" pressures are the same for both switches.

A one-wire switch grounds through it's metal body, where it contacts the aluminum housing of the compressor.

Given that the switch is sealed with an O-ring, and the wet side of the O-ring is going to be bathed in refrigerant oil, using the switch body is something of a dodgy grounding scheme.

OTOH, with a 2-wire switch, when the contacts close, the second wire, tied directly to a good ground with a low-resistance wire, has no problem conducting current.

So the 2-wire switch is nothin' to be scared of, IF (big IF) the switches trigger at the same pressure.

The problem is, the one wire switch setup was meant to close the recirc door when it trips, not shut off the compressor. You need to wire the 2-wire switch in series with the LP Cycling switch for safety.

 

[Donald Mitchell]

I have everything ready to wire and I thought I would ask before hooking them up, if this switch has a polarity, i guess because it only plugs in one way.

 

[PlayingWithTBI]

I thought I would ask before hooking them up, if this switch has a polarity, i guess because it only plugs in one way.

It doesn't matter, it's just a simple single pole single throw type switch.

 

[L31MaxExpress]

Definately make sure to get the right switch. The recirculate switch closes at 250 psi and reopens around 160 psi. The high pressure cutout switches open at 430 psi. Personally I would ground the recirculation wire and install a 430 psi switch in the path of the ac clutch wiring. Otherwise on R134a on a hot day with a hot interior the head pressure may open the high side pressure relief in best case or worst case blow up a discharge hose or compressor. Where I am here in Texas, when it is 105°F or more outside and you have the interior at 140°F or more it is not uncommon for the high pressure switch to turn the ac off a few times until the interior cools down.