AC Compressor High Pressure Switch?

Post by **Ozark Lee** » 31 Aug 2010, 17:23

I think the way I would tackle this is to work backwards from the compressor to see where you have voltage or don't have voltage.

On the turbos the Motonic ECU gets a high pressure limit and shuts everything down.

You will need to evacuate the system as all system pressure will be lost. It is your call on how you do that. Be sure not to leave the system open for an extended period of time or you will need to replace the receiver/accumulator/drier (All the same part with different names). Humidity will kill the desiccant. You will also need to pull a vacuum on the system prior to recharging with R-134A.

High pressure limit switch failures are quite rare.

...Lee

Post by **Red-Arrow** » 29 Sep 2010, 05:03

I just discovered what you guys are talking about now.

The AC system is not leaking and when I gave the AC compressor a positive wire feed from the battery the AC clutch engaged right away and the AC was very cold. I used a paper clip to jump the low side port near the fire wall and the AC compressor still didn't turn on but I heard the engine labour and bog down a little for some reason.

I pulledthe glove box and removed a standard Bosch/ Volvo Green relay no.9494787, I think its suppose to be for the AC compressor? the contacts were pitted but it seems to work fine.

I can't find the relay or main power source for the grey wire that feeds the compressor? Any help would be much appreciated.

Post by **Ozark Lee** » 29 Sep 2010, 19:06

If the relay has pitted contacts, either replace the relay or burnish the contacts inside of the relay - I would go the replace route since that relay is very simple and very cheap. It may test fine with no load but once the clutch tries to kick in the relay may have too much resistance to get the job done due to a voltage drop across the contacts.

...Lee

kenn · Post by **kenn** » 30 Jun 2011, 19:01

1992 740 Volvo. Had AC service. No leak issues. AC worked sometimes. Where I live, Bakersfield, CA, sometimes is not good enough. I went with the "Bypass the Switch" solution. The switch was easy to find. I followed the wire connected to the AC back to the switch. I then simply got a piece of similar wire (I'm thinking 12 or 14 gage) and ran the wire around the switch, cut the plastic sheath off the existing wires to expose the wire on both sides of the switch, then wired in my bypass wire. Viola! I used electrical tape to seal the connections. AC works perfectly now. This saved me $1000+ as quoted from my AC mechanic. So far (just completed and tested), GREAT! If anything changes I'll come back here and update this reply. I have 199k+ on this Station Wagon and still going strong.

Post by **pkc303** » 01 Jul 2011, 05:55

One bar is 14.7 at sea level. It decreases as the altitude increases. Los Angeles is 125' MSL, so it doesn't matter, but to the folks in Denver or Amarillo, it might make a difference.

Dome · Post by **Dome** » 14 Jan 2012, 17:57

I need to jumper the pressure switch so the compressor comes on to re-charge my 1984 242DL anyone know how to do this. I'm not sure where to jumper from...

Thanks

Post by **burnout8488** » 16 Jan 2012, 00:06

Ozark Lee wrote:You will need to evacuate the system as all system pressure will be lost.

Topic got bumped so I thought I'd clarify.

Lee - This switch actually has a Schraeder valve underneath it. No need to evac to replace the high side switch! (The one behind the passenger headlight)

Dome - The 240 section of the forum might be more helpful for you.