PCM / Flash differences between Auto and Manual HVAC?
Thread Starter
Racer
Joined: Jan 2020
Posts: 275
Likes: 39
PCM / Flash differences between Auto and Manual HVAC?
Odd one, but is anybody aware of PCM differences for cars with Auto vs Manual climate controls? Specifically a 1998 manual trans car. I didn't see anything in VCM editor besides disable limits for A/C.
It appears the Manual variant's "A/C request" signal is an on/off voltage where the Auto climate control uses serial data for "A/C request" instead. The service manual shows the PCM wired up with both, although in the HVAC sections it only shows one or the other. I've read some other GM vehicles having unique PCMs for this and some guys struggle during engine swaps to get a non serial(for A/C that is) PCM to integrate the A/C easier.
If someone has a 98 PCM(or year equivalent) harness laying around from a Auto Climate car can you tell me if this wire is pinned?
C1(Red Plug) -> Pin47 (Green/White)
I'd check my car but it's in storage at the moment and its cold in NY. I'm converting to manual controls and this A/C situation is the only thing I don't have a solution for just yet.
It appears the Manual variant's "A/C request" signal is an on/off voltage where the Auto climate control uses serial data for "A/C request" instead. The service manual shows the PCM wired up with both, although in the HVAC sections it only shows one or the other. I've read some other GM vehicles having unique PCMs for this and some guys struggle during engine swaps to get a non serial(for A/C that is) PCM to integrate the A/C easier.
If someone has a 98 PCM(or year equivalent) harness laying around from a Auto Climate car can you tell me if this wire is pinned?
C1(Red Plug) -> Pin47 (Green/White)
I'd check my car but it's in storage at the moment and its cold in NY. I'm converting to manual controls and this A/C situation is the only thing I don't have a solution for just yet.
Thread Starter
Racer
Joined: Jan 2020
Posts: 275
Likes: 39
Just my preference. I feel some cars do it better but in the vette the A/C comes on at weird times and I'm really a full blast hot or cold type of guy. I just prefer the ***** lol. I hate pressing that fan button to get full speed. Anyway I got my car out for the season and was able to do some digging.
Turns out my car has the A/C request wire populated at the ECU for manual controls variants(pin 47 green/white). I didn't get a chance to go further and find out where it gets terminated or to see if I can even activate the A/C from this. Next week or so I will try this. Hoping the PCM will allow either method. Will have to disconnect the digital control most likely during the experiment to avoid conflicts.
Turns out my car has the A/C request wire populated at the ECU for manual controls variants(pin 47 green/white). I didn't get a chance to go further and find out where it gets terminated or to see if I can even activate the A/C from this. Next week or so I will try this. Hoping the PCM will allow either method. Will have to disconnect the digital control most likely during the experiment to avoid conflicts.
Thread Starter
Racer
Joined: Jan 2020
Posts: 275
Likes: 39
It works. You need to have the digital climate control disconnected from the car and you can toggle the green/white wire at the PCM to run the A/C. This was the last major hurdle for the conversion. Hoping to finish over the next week or so. Dealing with the dual temp blend doors is last "unknown" as far as how I will do it but it will work. I'll post a write up of how I did it when its all debugged.
