'94 Q45 Condenser fan not blowing

[bfbass]

94 Q45, 153K miles. All original.Recent spark plug change.

My condenser fan for the AC is not blowing at all, even when the temp is really hot. When I come to stop light, the A/C compressor switches off. I have tracked the problem to the cond fan, which is not circulating air over the condenser, so the high side switch cuts the compressor off, which leads to hot air blowing.I checked the fan separately, and when I put a 12V supply to it directly it runs fine. I have replaced the solenoid(with a known good one) in the fuse block under the hood. I also checked the fuse for the cond fan under the hood.I have also check my shop manual, but can find nothing on how to troubleshoot this.Any ideas?

[DAEDALUS]

As I recall there are 2 switches that are wired in parallel to the relay; either of them will start the fan. One of them is the temp sensor, and the other one is a separate pressure switch on the high side, on the line near the drier. The manual does show diagrams/locations of these components, as well as a schematic of the system. You can try shorting the lines to each of these inputs to see if the fan turns on. If yes, then the switches are bad. If not, then you've got a wiring problem somewhere. Another point to diagnose is at the relay. Check if there's voltage from either switch going into the relay, and measure the resistance of the 2 terminals going to the fan to see if there's continuity.