Installed a good condenser from a 1994,,used new seals & evacuated for 30 mins w no leaks,,charged the system w 2 lbs of 134a.
triedto start the Ac & run the blower on high & only get it to run if I jump the dryer plug ,I dont have much experience w Ac & the FAQ doesnt seem to cover this sequence.Any ideas??

Hi Blindboy,

First is to test if there is still pressure after your refilling. With engine OFF, connect AC gauges to the refill port ie. the low pressure port. Read the pressure. This also to test for possible leaks after refilling. Another test for leaks is by using soap bubbles but this best is done right after refilling.

Secondly test the low pressure switch as in my earlier reply to Mr Pelchat. Sometimes the act of testing the switch (as described) could make it work again. If it doesn't then replace it. If you have pressure tester the switch closes (means ON) at around 60psi and opens (OFF) around 29psi.


Amarin.

Just to help fill the time before Amarin tells you more...

On my 940, in a no compressor engagement situation, the switch is bad if jumping the low pressure switch on the dryer engages the compressor. They can be removed with a pressurized system. I don't know if they can be tested otherwise
--
89 240 wagon, 94 940, 300K, 94 940, 141K

Hi Mr Pelchat,

Thanks for the heads up : )

Regarding testing the switch, I don't have any pressure tester. So I devised a method to test it. Unscrew the switch out and there's a small hole (about 1 mm size) within the threaded portion. Behind the hole is the metal diaphragm to sense the pressure and behind the diaphragm is the electrical part of the switch. Use something small and blunt (a wooden pick or blunt metal object maybe) to poke into the hole. Should feel a click when poked hard. Connect the switch's electrical terminals to multimeter set for continuity test. The switch should close (means ON) when poked and clicked.

Amarin.

Amarin, Since you are on the line... I've had many problems with AC over the years on the 940s, mostly due to aging control units. When things aren't working, I never know if it is electrical or something else.

Recently I had an intermittent no-engage symptom. I swapped in a known good controller. Didn't help so I dug a bit more. Found that fiddling with the wire connector of the low pressure switch would often engage the compressor. Treated the connector but it wouldn't work consistently. Jumped the connector and it engaged. Put in a known good used switch and it engaged and working for 2 weeks now.

I just tested the switch as you directed and I get continuity. In situ the switch was intermittent at best yet it tests good. Maybe heat related. Any thoughts?
--
89 240 wagon, 94 940, 300K, 94 940, 141K

To answer your intermittent no-engage symptom the issue could lie in
1) increased clutch gap - but this mostly happens when engine is hot - easily diagnosed by measuring gap
2) faulty control unit - cracked solder at the internal relay inside unit - easily diagnosed by no power at switch/pressostat electrical plug when engine running, AC button ON, blower ON
3) faulty switch (pressostat) and/or its electrical connector - see below

I suspect your intermittent issue is possibly number 3. Repeat the test on the switch again but this time keep on poking the hole ie. keep switching it ON while wriggling the switch's terminals. I had an issue of loose switch terminals last time when I used non-OE part. It was a Santech switch. Problem solved when I ordered OE switch/pressostat from volvopartswebstore.com . It was quite at a price but problem solved.

If your switch's terminals turned out to be solidly ok during testing then it could be its electrical plug instead. Try using small jewellers screwdriver to tighten the internal contacts but this usually temporary fix. Its best corrected by splicing in a new plug. Look for already wired/spliced Bosch EV1 type electrical plug at eBay for replacement (same plug used for Bosch fuel injectors/idle control valve). Polarity doesn't matter here. IME once the internal contacts (known as "junior timer contacts") within the electrical plug became loose replacement is the only option.

Amarin.