The 1947 - Present Chevrolet & GMC Truck Message Board Network - View Single Post - AC compressor relay and Trinary switch wiring question

Davidf · 09-21-2021, 11:51 AM

Where is the ECM in your diagram? You want the ECM to control the compressor so that the added load on the engine is compensated for by the ECM. Usually a/c request is straight to ECM (through HP cutout switch) and the ECM output (pin 43, ground output) goes through the relay. Fan request is via the ECM as well. Why do you need a trinary switch? If you want fans on when a/c compressor is on, then just wire the fans through another relay in series to the a/c compressor relay (a/c relay triggers fan relay).

Note: Your a/c on/off wire (from control panel) IS the a/c request wire.

https://lt1swap.com/99-02acwiring.gif

09-21-2021, 11:51 AM	#2
Davidf Registered User Join Date: Nov 2014 Location: Austin Posts: 749	Re: AC compressor relay and Trinary switch wiring question Where is the ECM in your diagram? You want the ECM to control the compressor so that the added load on the engine is compensated for by the ECM. Usually a/c request is straight to ECM (through HP cutout switch) and the ECM output (pin 43, ground output) goes through the relay. Fan request is via the ECM as well. Why do you need a trinary switch? If you want fans on when a/c compressor is on, then just wire the fans through another relay in series to the a/c compressor relay (a/c relay triggers fan relay). Note: Your a/c on/off wire (from control panel) IS the a/c request wire. https://lt1swap.com/99-02acwiring.gif Last edited by Davidf; 09-21-2021 at 12:00 PM.