Let me provide some background information on this. First of all its a 95 Chevy C1500 and not a 3rd gen but that shouldn't have much effect on this. What I've got is a set of dual fans for a 34 inch radiator. I am running the MAF code for the PCM which has one PCM controlled fan output written into it which turns on with either an AC request signal or when it gets to a set temperature. That is all fine and well and I used that for a low speed (series) operation for a couple years without too much trouble. The high side pressure did run rather high at times though, up around 325 at idle in 100 degree heat and after blowing out the front seal last summer I want to remedy this. What I've done is set it up in series parallel configuration like GM has done for years. Again the PCM will be in charge of the majority of the cooling via low speed fan operation and the idea was to have a pressure switch turn the high speed fans on as needed. Finding the correct switch is proving to be a real PITA though. What I've got right now is a condenser fan switch for a 1995 Olds 98 3.8 liter thats supposed to be normally open and turn on at 210 and off at 160. I installed the switch and wired it yesturday, ground on one side, to the high speed relay on the other side which would provide a ground for it and turn it on. What it did was turn the high speed fan relay on as soon as I plugged the switch it. I ohmed it and for whatever reason the switch seems to be normally closed though its not supposed to be. The schematic for the Olds 98 shows the switch being normally open just like I need. At this point I'm not sure where to go with it. To do what I want I REALLY need a normally open switch and I can't seem to find one that is for R134a that will screw onto the condenser. I believe its 10mm x 1.25 thread with an oring. If anyone can steer me in the direction of the switch I'm after I would really appreciate it.

 

*cricket noises*

 

The one thing I can offer as a possible resource is Autoaire. They are an AC supplier and they have a wide variety of switches available. I have used many of their components and their quality is good. They can probably match a switch to your specifications. Another option would be to use the Standard Motor Products application guide. It includes a listing by part number with specifications for each P/N. Can't you use the high pressure switch from any 3rd gen with dual fans? The high pressure switch turns on the auxiliary fan by closing the relay's primary ground circiut whenever the AC is on. I don't know what the pressure spec is but it works for the R12 system. May be too low pressure for R134.

 

If a 3rd gen switch has the same threads that would work. The only reason I went with the olds 98 switch was because it was the first I came across that I knew had the correct threads and by everything I can find, worked exactly how I need it to but obviously doesn't. What are the threads like on the 3rd gen switch? I believe the one I'm needing is 10mm x 1.25 oring sealed.

 

I can't remember. It's been a while since I dealt with 3rd gen AC.My IROC is AC delete. But that thread size sounds about right.

 

Is this the switch you are referring to?



Says the activation pressure is 250 and deactivation is 185 which is about right for high speed fans. The schematic checks out but so did it on the switch I bought initially. Not too sure on the thread pitch though. Can someone verify this?