A/C without an ECU in an S13?

[StorminMatt]

I’m currently in the process of doing an E-Rod swap in my S13. This is a ‘California smog legal swap in a box’ sold by GM, and includes an LS3, wiring harness, ECU, cats, etc. Compared to other GM ECUs, the E-Rod ECU seems to be very ‘stripped down’ and ‘standalone’ - it doesn’t seem to have any kind of controls for A/C. This means that I need to run the A/C without any kind of ECU.

Now in the S13, there is a lead coming off the A/C amplifier that goes to pin 44 on the S13 ECU. This seems to tell the ECU when to turn on the compressor and fan, subject to other conditions (such as whether you are driving WOT). The ECU then sends a signal out pins 43 and 47 to switch on the relays for the compressor and fan. But since I won’t be running the S13 ECU (or ANY ECU with controls for the A/C system), how should I trigger these relays? Should I just connect the A/C amplifier output to the relays? Or do I need something else, like perhaps another relay to control these relays?

[JrDarknes]

You kind of need to reword a few things on your second paragraph but I get what you're asking & you're correct. You will need another relay to control those relays. It will be a ground based relay.

Your talking about terminal 43 on relay 1 (A/C Relay) and terminal 47 on relay 2 (condenser relay).

Both of those terminals are ground based. So this means that when you click the A/C button on your climate control it grounds at the climate control and triggers those relays to activate.

So to make both of those relays work you just need to make a relay that triggers a ground signal and wire them to terminals 43 on relay 1 and terminal 47 on relay 2. One issue with this though is that you kind of need sometype of ECU for your thermo control amp.

The thermo control amp senses the evaporator’s temperature via a temperature sensing probe that is located in front of the evaporator core. The thermo control amp will then inform the ECU whether to cycle the compressor magnetic A/C relay ON or OFF.


You can try to use the ground relay without the thermo control amp but there a chance you could freeze up the evaporator.