The car: 1990 740GLE 16 valve. The air conditioning seemed to be working sporadically, so I converted it to R134. I did it the right way, with the OEM Volvo conversion parts and using a vacuum pump and proper gauges.

It worked well for two days, but after that the compressor clutch would not engage when the A/C was switched on. There was no loss of refrigerant. Jumping the contacts for the low-pressure switch on the receiver/drier does not cause the clutch to engage. I believe that the relay that delays the switching on of the A/C for ten seconds is working, as the engine idle is bumped up right on schedule. The compressor clutch does engage if I connect the black wire that comes out of the clutch directly to the positive terminal on the alternator. With the A/C switched on, I get 12v at the red/green wire that connects to the clutch wire.

I don't have immediate access to a genuine Volvo wiring diagram for this car. The 700/900 FAQ on this site has discussions of the 91-on cars that have a climate control circuit board, but nothing about the B234F cars. A Mitchell repair manual on CD that I have has an electrical component drawing which identifies an "A/C cutout relay (B234F)" located in front of the strut tower on the driver's side of the engine compartment. The A/C wiring diagram the Mitchell manual has appears to be somewhat generic, and I cannot locate this relay in it. This post: http://brickboard.com/RWD/volvo-952825.html also indicates that there is such a relay, although it suggests that the relay is behind the right front headlight; I see no such relay in that area on my car.

My car does have a blue-cased rectangular relay, part number 3523737, (also says "12V 898169") mounted in the location indicated in the Mitchell manual. It has four wires - black, black/green, red/green, and red-white - going into it. Is this relay the component that switches the compressor clutch on and off in the B234F cars? Is it possible that this relay has a bad solder connection or some other internal fault such that it is providing 12 volts, but not enough "oomph" (amperage? I'm hopeless with electricity) to engage the clutch? Before I did the R134 conversion, there would sometimes be a rapid clattering noise from the compressor; I am now wondering if that may have been the clutch engaging and disengaging as a result of a marginal power supply.

The blue relay appears to be manufactured in such a way as to make it impossible to open up. I live close to a pick 'n pull junkyard which typically has a number of Volvos, but I've never seen a B234F there; do any other Volvo models use this blue relay?

Any suggestions appreciated.