2003-up Silverado AC request type

[G-Body]

I figured out why my fans would not engage.

My A/C Fans Disable speed was set to 0mph. I did not think this was a problem as the HPTuners description states "A/C Fans Disable speed: If the AC is on both fans will disable if speed is above this value and other thresholds are not met". Now my Fan 1 AC enable pressure was already set to 225 and disable to 220 (I`m not running a pressure switch so I faked it with a resistor that reads 228psi) I assumed that since my a/c pressure was above 225 the fans would enable as "other thresholds" would be met.

I changed the AC Fans disable speed to 40mph and the fans came right on.....always on... (due to my AC pressure constantly being 228 even with the A/C turned off). I thought I was onto something and tried raising the Fan 1 AC enable pressure to 250 thinking that would allow the fans to turn off when the A/C request was off, but turn the fans on when the request was on and speed was below 40mph. No luck there, now the fans would not enable regardless of speed or A/C request status. Looks like I will either have to put a pressure sensor inline to monitor the actual pressure, or use a relay to enable to a/c pressure sensor resistor bypass only when the compressor is running.

Cliffnotes, In order for the fans to activate BOTH the Fan 1 AC enable pressure AND the A/C Fans Disable speed conditions must be met. Not either/or like the HPT notes would lead you to believe.

[ntwifi]

I have successfully made the a/c request work with a computer off of a 2003 Suburban, and a Vintage Air A/C system.
1. I changed the serial cycle to analog. (it would not work with analog cycle)
2. Wired the compressor clutch output of the aftermarket ac to connector C2 pin 17 applying +12v for the A/C request.
3. had local A/C shop who can crimp hoses install sensor port inline on my hot gas hose. (I feel this is where everyone is missing out, with the factory sensor, the pcm can cycle fans and compressor, and we can adjust the pressure where we need the fans to cycle)
4. Set up pressures for fan cycling on pcm
5. I inserted terminal in 42 of connector C1 for fan 1 and wired up realays and fan
6. Inserted terminal in connector C2 uses terminal 33 for fan 2 and wired up relays and fan
7. I used factory fuse/relay block so all I had to do was wire relay to compressor clutch

Again, I think we are complicating things too much by taking out the high pressure sensor, it cost me $37 in parts and labor to have it installed in my refrigerant line, and I feel that all the systems are working so much better with it.

[HartRod]

I have successfully made the a/c request work with a computer off of a 2003 Suburban, and a Vintage Air A/C system.
1. I changed the serial cycle to analog. (it would not work with analog cycle)
2. Wired the compressor clutch output of the aftermarket ac to connector C2 pin 17 applying +12v for the A/C request.
3. had local A/C shop who can crimp hoses install sensor port inline on my hot gas hose. (I feel this is where everyone is missing out, with the factory sensor, the pcm can cycle fans and compressor, and we can adjust the pressure where we need the fans to cycle)
4. Set up pressures for fan cycling on pcm
5. I inserted terminal in 42 of connector C1 for fan 1 and wired up realays and fan
6. Inserted terminal in connector C2 uses terminal 33 for fan 2 and wired up relays and fan
7. I used factory fuse/relay block so all I had to do was wire relay to compressor clutch

Again, I think we are complicating things too much by taking out the high pressure sensor, it cost me $37 in parts and labor to have it installed in my refrigerant line, and I feel that all the systems are working so much better with it.

What sensor did you use? Can you draw a diagram of your setup and post your tune? Thanks in advance.

EDIT: How is over pressure protection accomplished? Do you have a separate binary switch in the system?

Here's a link to another thread where this is discussed: http://67-72chevytrucks.com/vboard/s...d.php?t=709611

[LSxpwrdZ]

Pretty sure he just wired up the AC Pressure sensor that you would normally have on a Fbody.

[HartRod]

Pretty sure he just wired up the AC Pressure sensor that you would normally have on a Fbody.

I was thinking he used the truck pressure transducer and not the Fbody pressure switch.

[LSxpwrdZ]

I was thinking he used the truck pressure transducer and not the Fbody pressure switch.

My car's do not have a switch. Its a 3 wire pressure sensor. The Fbody's reference actual pressure and not just a switch.

[HartRod]

My car's do not have a switch. Its a 3 wire pressure sensor. The Fbody's reference actual pressure and not just a switch.

So do the trucks.

[95silvia]

What it comes down to is if your ecu has the IAC driver installed. If you choose analog or serial the computer will look for a 3 wire pressure sensor. If you choose analog cycle or serial cycle the computer will look for a 2 wire pressure switch. All the information you need has been posted on ls1 tech in a thread titled "A/C request Blue/Green connector ECU". The forum wouldnt let me post the link.