I know this has been discussed and I have seen different answers when I search. Since I finally got the AC hooked up on my Lt1 swap, I am using the 3 prong pressure switch on the high side. My question is do I need to remove the valve from the fitting on the hard line? If so, I won't be able to connect a gauge on the high side since I only have one port on the hard line. I am running everything through the computer so I would like to keep everything "factory" but I don't mind using resistors if I have to.

 

The 4th gen a/c uses a sensor, not a switch. Sensors and switches are kind of considered the same thing if you try to order one though, a sensor may be listed as a switch. I never got the 4th gen a/c sensor to work because it wouldn't physically go on, it has different size threads and won't go on. I also haven't gotten around to trying my 1990 grand am sensor (uses the same 3 terminal plug as the 4th gen a/c lt1/ls1 sensor). Would have to re-program the pcm to fool it or fool the pcm by using a resistor for the 2nd sensor. LT1's use 2 sensors in the a/c and the 2nd sensor isn't really needed. As I understand it, the 2nd sensor is inserted into the evaporator on LT1's and is just a fail-safe of some kind so the a/c is automatically turned off when outside temperatures are below freezing.

https://www.thirdgen.org/forums/ltx-...h-gen-ltx.html
https://www.thirdgen.org/forums/ltx-...r-control.html

 

I've got the temp probe installed and I have the 4th gen pressure switch installed on my high side but I have a very bad feeling I will have to remove the shrader valve to get the switch to capture the pressure. This is my concern. If I ever want to hook up some gauges, I won't be able to cuz when I remove the sensor, obviously everything will leak out. Unless, there is another switch, such as the one referred in your links that don't require the removal of the shrader valve.

I'm pretty sure I can figure out the resistance of the pressure switch but this won't be a good idea since the pcm will never shut off the compressor if there is a problem on the high side.

 

I threaded my 3 wire sensor in place of the high pressure 2 wire switch on the hardline that runs along the PS frame rail. Been working fine for at least two years like that.... perhaps three, but I lost track of when I did the swap originally.... lol

 

The older style pressure switch (1990 grand am) goes right on the high side without having to remove the shrader valve, the threads match up unlike the 4th gen sensor. Haven't wired it up yet though. The car I removed it off of still had the valve installed.

 

I need 4th gen 3 prong high presure sensor used are will any store part have them??????????? thanks

 

will a 4th gen high pressure sensor fit in place of the old 86 camaro sensor lt1 swap ? 3 prong thank you

 

No. 4th gen a/c sensor will not work because threads are the wrong size. Needs to be a 1990 grand am 3 prong sensor. Also need the LT1 temp probe or fool the LT1 pcm to think it is seeing a correct temp probe temperature. Also the 3-prong sensor will not fit in place of the 1986 low side a/c switch, the 1990 grand am 3 prong sensor installs on the high side.
Other notes - Low side switch is not needed if using the 3 prong sensor. Low side switch and relay can also control the a/c if not using the LT1 PCM to control it via the sensor.

 

frist thank you for your help question 1 what is a Lt1 temp probe is this the Lt1 temp sensor on the right head causes my lt1 harness has a 86 temp style connector and I had put the old 305 temp sending unit thanks again

 

The temp probe is part of the LT1 a/c system only. It sticks into the fins of the evaporator and the electrical connector for it is in under the passenger side glovebox/dash in 93-97 LT1 f-bodies.