Hi everyone. New here, got a 1993 Cutlass Ciera * with the 3.3 and 4 speed auto. Got it pretty cheap and fixed all the mechanical issues. Been using it as my daily driver because it has good fuel economy and decent ride, until this present mystery showed up. Let me begin...

I had replaced the rad fan last summer because the original one vibrated and was noisy when operating. I also put on a serpentine belt to bypass the AC compressor for the winter months and also because the compressor has a noisy bearing, of which I hope to replace this coming year.
To operate the rad fan when it got to a certain temp on the gauge I just put my heater controls on AC or defrost, then the computer would send a signal to the relay to operate the fan.

Now it won't do that and the temp climbs. What I've done up to this point is:
1. Checked for proper signal to the relay by finding the wire which gets it'* communication from the computer to connect the contacts in the relay to start the fan. I shorted it out, the relay connected and started the fan.
2. I pulled the dash apart to get to the heater controls to make sure everything there was working properly. Checked for continuity on the AC switch which activates the system. Even took it apart to check for rust or bad contacts, of which it was perfect, then slimed it with some new dielectric grease and re-installed it.
3. Checked for continuity on all the wiring involved with both the AC and cooling system, even up to and from the computer. No breaks anywhere, but I did find some fuses under the dash behind the glove box which I couldn't find anywhere on any wiring diagrams that I searched for on the internet. The fuses were fine and re-installed.
4. Replaced the coolant temp sensor and temperature sending unit. When I shorted out the 2 terminals on the diagnostic connector under the dash the rad fan came on when I turned the ignition switch on. And fortunately, no codes came up after I went through the sequence. Also, the temp gauge works better now, where before it never registered higher than the first mark on the face and now it is over that mark. On my car, because it'* a Canadian model the gauge registers in Celsius and the center mark is 100 degrees (212 fahrenheit).

One last note: before this happened I may have heard a click(?) under the passenger side of the dash just before this all happened. Is there another fuse block or relays under the dash of which GM never told anyone about? I'm 54 and have been working (playing) with anything automotive related since i was 12 so I know the manufacturers have done some weird things to their products that **** off people like us later on when we try to repair these vehicles.

If anyone has any thoughts on any of this, I'm all ears! Thanks...

Can you backprobe the wires toward the switch and see if it is supplying power as it should while everything is hooked up?

Well after all this time thinking about this problem, I found a page on the internet with someone who has the exact same problem. With the diagnostic page he provided I determined that the high pressure switch, mounted on the back of the compressor, is the culprit for my rad fan and compressor not engaging.

Now my question is: how do I go about replacing that switch? Do I have to have the system evacuated? And how hard is it to change while the compressor is still installed on the car?

I believe it does not need to be evacuated.

Start taking it off. If it starts leaking (I don't think it will) just tighten it.

Just adding my "two cents" here. Why don't you get a hold of the diagrams for your HVAC system? The fans are supposed to come on automatically at about 212 degrees Fahrenheit and 225 for both. Instead of fooling the system by turning the A/C on that would be the best way IMHO. Also try searching YouTube for your "Cooling fans not coming on" Buick Century,Olds Ciera.

If you need any info for your Cutlass I have the factory service literature.

The computer will normally look at the low side to determine if there is enough charge in the A/c system to engage. Once it drops below about 20psi, the switch opens and the computer will not command compressor engagement, and in turn, kick the fans on.

How hot is the vehicle actually getting? Normal operating temperature is likely just past half on the gauge, I would let it sit there and idle until the 3/4 mark to confirm there is even a problem.

Questions about operating temps are relatively common, and they usually involve the user believing the engine should operate cooler than it actually does. These engines are solid iron. They run better when they're hot, and they are much more tolerant of heat than other aluminum block/head engines.