Refridgerent Containment Switch Bypass

[Racer X]

The replacement high pressure line I used in my '94 doesn't have the fitting for the refrigerant containment switch, so I'll need to bypass it. Prior to '93, there was no switch, so I'm not super concerned about things getting all explody.

I know the switch plays a part in the fan speed being raised when the A/C is running, but the diagram does nothing to show the internal connections of the switch. Does anyone have any insight?



Thanks.

 

[Slo-Sho]

My 2 cents

If you bypass the switch, the question is will it make the fans run on Hi speed all the time? I say that because if the fans no longer have the Hi speed function, the higher head pressures of the 134a can possibly make the a/c blow off valve go kaboom if it gets too hot outside. And then obviously you just wasted all your time and effort oh and money.

 

[jelloslug]

Prior to 93 the AC system was also R12 which operated at a lower pressure. With that said I and many others have older SHO that don't have that switch at all and the AC works just fine.

 

[Racer X]

If you bypass the switch, the question is will it make the fans run on Hi speed all the time? I say that because if the fans no longer have the Hi speed function, the higher head pressures of the 134a can possibly make the a/c blow off valve go kaboom if it gets too hot outside. And then obviously you just wasted all your time and effort oh and money.

- I don't have a choice but to bypass the switch, as there's no provision to fit the switch on the new high pressure line. Unless you or someone else has a source on 94+ high pressure lines with that fitting, new or used, a bypass is my only option.
- My 92 was converted to R134a without a high pressure switch, and I never had a blow-off event. That said, that fan only had one speed: Gale.

I can fabricate a circuit to mimic the switch operating during a high pressure event, but first I need to know it's internal connections.

 

[hawkeye18]

This is from the '95 EVTM. As you can see, the bottom two pins form a NO (normally open) switch. When the high side pressure reaches 325psi, the switch closes, applying ground to the High Speed Fan Enable circuit from the CCRM. This is what controls the fan speed, and basically whether you short those two pins or leave them open is going to determine whether the fan stays on low or high. This is independent of, and superseded by, the fan speed commanded by ECT - e.g. if the ECT commands High fan speed, it'll go high whether the HP switch is closed or not.

The top two pins are normally closed until the high-side pressure gets to 430psi, whereupon it'll open the two pins, opening the clutch cycling circuit and disabling the AC. This is a safety measure meant to keep the high side from exploding - i.e. if the orifice valve gets completely clogged. It closes back up at 250psi.

So if you're going to omit this switch, which you are obviously going to do, you need to short the PK/LB and R/Y wires (this will not disable the clutch cycling switch, merely the high-pressure safety switch part). It is up to you whether you want to short the DG/O and BK/LG wires or not. Frankly, I would personally wire it up to a switch in the cabin. On-command fan speed! You can have it be always high if you're racing or something.

 

[rubydist]

Your other alternative is to keep the switch in the connector, and just wire it up securely somewhere. Since the switch is n/o, the a/c will work, but you will not have the high speed fan automatically.

 

[JRA2000TL]

So the R12 systems don't have the valve on the accumulator canister then and the R134 systems do? Noticed my 89 had the switch but it's been converted.

Guessing it's like jelloslug said in the fact that 134a operates at a higher pressure and needs a switch to regulate it; thus Hamal's cocern for blowing stuff up on a 134a without it?

 

[projectSHO89]

R134a systems were required by regulation to have the high pressure cutoff. It was all part of the same government regulation that required the transition from R12 to R134a.

The same regulations required retrofitted systems to have the HPCO switch added, a requirement almost universally ignored.

 

[rubydist]

I've done a couple conversions w/o the high pressure cutout, and never ever had any issue.

 

[jelloslug]

So the R12 systems don't have the valve on the accumulator canister then and the R134 systems do? Noticed my 89 had the switch but it's been converted.

Guessing it's like jelloslug said in the fact that 134a operates at a higher pressure and needs a switch to regulate it; thus Hamal's cocern for blowing stuff up on a 134a without it?

It's not the pressure cycle switch. It's another switch that on the high pressure line.