Ok, I wrote it in a hurry, so I'm rewriting to clarify...the car is an 87 TPI 305.

Problem 1: Secondary cooling fan NEVER comes on. It does not run no matter how hot the coolant gets, and does not run with the air conditioning on.

Problem 2: A/C compressor constantly cycling on and off. It switches every few seconds.

Other things I know: A/C system is fully charged, works well with good airflow. I have replaced the coolant temperature switch in the passenger side cylinder head. The secondary cooling fan does run if I ground the wire to the switch. So, I know that the motor is good. The relay is also good.

I am wondering: Are the two problems related? As I understand it, the secondary fan is controlled by both the temperature switch and the A/C high pressure switch. I would think that if the temperature switch is bad, the fan should still run with the A/C on (is it an either/or condition, or when both criteria are met?). So, I am thinking that the high pressure switch is at fault. I'm thinking about replacing it today, but figure that that will discharge my a/c system when I do. So, if anybody knows the dual fan system well and can lend some input, I'd appreciate it. By the way, there is a lot of info on this in the archives, so this is the result of my research. I'm thinking about buying the Buick temp switch and the a/c high pressure switch and replacing both even though I have already replaced the temp switch with a stock rated one. So, if know what's up, talk me into it or out of it. Thanks.

 

Hook up with a gauge manifold and check the system pressures. A clogged condenser can do the same thing. I'd be interested to see your numbers.

 

That's something I have sort of been thinking about doing tonight. It's a tool I don't have though. Maybe it's finally time to go ahead and make the purchase, although that would ensure that I'd never need it again. That's how it usually works out.

I wish I had an internet hookup at home now. Going to the library to use it just isn't gonna cut it much longer. Thanks for the idea though, I'm glad the trip here wasn't for nothing. Maybe I'll check out a literary classic or something while I'm at it...

 

Well, I've done some shopping for manifold gauge sets. Not exactly cheap, but looks like I could have a decent R-12 set for around $60. Before I jump into that, though, I'd like to know a little more about how the high pressure switch works (also, I'm not exactly sure where it is). I've tested the two things that I suspect could be the high pressure switch, and they are shorts under all conditions I've tried. Is this correct? No matter if it should be that way, or not, something should happen in one of these two cases. 1: put a jumper across the terminals on the connector to the switch. 2: Go for the opposite and just unplug it ensuring it is then an open switch. Seems like one of those two cases should cause the compressor to run constantly and the fan to turn on.