Okay guys, I was curious on how the thermostat AC switch looked and I had a regular switch to install, so I took the thing apart and then realized I can't put a switch to a newer one on it. It's a 1984 245 GL.

What is the wiring for the switch? I looked at a diagram and it shows only a green wire.... When I know there is also a red and white, and two green wires, and maybe a red one. Where do they connect to the switch?

 

to the forum VolvoPrince

I don't know but hopefully someone will be along shortly who does.

 

looking it up now, at least if I have a 84 diagram (I'm missing some from the early 80s)... ah here it is.

k, those shows two green wires, one from pin 87 of the 'delay relay', and the other goes to the compressor clutch. the delay relay powers that pin 87 (from fuse 12) 10 seconds after alternator energizes.

 

Yeah I'm trying to figure out if the thermostat switch on the 740 is near the firewall top left under the bonnet, on top of the aircon hose & pipe stuff - when I pull off the socket and short circuit it (about 2.5 A load - clutch load?) the a/c stays on & actually cools, instead of switching on for just a few seconds every now & then - Do these things wear out?

 

there's 2 pressure switches in the A/C compressor circuit, one is on the AC Dryer/Reciever, thats the silver 'cannister' near the firewall... the other is on the lower manifold of the AC condensor, sandwiched with the radiator.

the signal goes from the dashboard A/C control unit, to the pressurestat on the dryer, to the pressurestat on the condensor to the compressor clutch. if either pressurestat is open, the compressor clutch never engages.

the one on the dryer checks to make sure there's enough pressure in the system, it goes open if there's not enough freon in the system.

the other one opens if there's too much pressure (can happen if the a/c freezes up due to lack of airflow on the evaporator).

 

the genuine volvo r134a conversion sticker on my 92 740 has different numbers for -91, and 92-, also different for NA and turbo. I think my 92 turbo is 0.96kg or something.

 

I might add, when its working reasonably well, 7/940 have very good HVAC.

 

What a good summary of the air con system!
Yeah, when I short out the dryer plug she gets nice and cold real fast. But if that's what's cutting out all the time does that mean there's not enough freon in the system? Could the switch be gone? When I wiggle it it seems to make the thing go on & off, even though the plug & socket seem OK. Can I just ignore that & keep it shorted - seeing as there's that other lower manifold switch (haven't seen that yet)?

 

yeah, could be a bad pressure switch, OR insufficient freon. Pretty sure changing that pressure-stat will require evacuating the freon, then recharging.

the lower manifold switch is for too MUCH pressure, which can happen if the fan isn't blowing sufficient air past the evaporator and the system freezes up.