PCM wont turn on AC compressor, can command it with controls.

[6speedblazer]

Working on a 2003 s10 that i swapped a 2003 silverado 5.3L into. Still using the factory 03 s10 blue/green pcm, but the donor engine tune as they shared the same pcm service number.

i changed the tune for drive by cable and a few other things. Filled up my AC and the compressor clutch wont kick on. I changed the AC type to analog cycling as its wired with a low and high pressure cutoff switch, just like the factory s10 was. The S10 was also set to analog cycling, so i figured it should work.

I can command the compressor clutch with the controls and it kicks on just fine, so i know the wiring side is correct.

attached is a current copy of my tune. do i need to change something else besides cycling type?

zr2 tune 102214 iat sensor calibration.hpt

[mecanicman]

Silverado has different ac control system than s10. S10 uses user interface, hi and low pressure switches for pcm to determine when to cycle. Silverado has hvac control module with class 2 data, low pressure switch, and ac refrigerant pressure sensor. You have control side of ac hooked up right(why you can turn ac on) but the pcm is not seeing the data it needs to turn it on.

[6speedblazer]

Silverado has different ac control system than s10. S10 uses user interface, hi and low pressure switches for pcm to determine when to cycle. Silverado has hvac control module with class 2 data, low pressure switch, and ac refrigerant pressure sensor. You have control side of ac hooked up right(why you can turn ac on) but the pcm is not seeing the data it needs to turn it on.

Exactly, that is why i switched the silverado tune to analog cycling. I have the system wired exactly as it was for the S10 (and later model express vans) that have analog systems. But there is no other data for the PCM to see, which is why i am confused. With an analog system there is nothing to tell the compressor to "cycle" on or off in its system besides the high and low switches once AC has been selected in the cab.

i have read that some people have had issues with this PCM and switching back to analog cycling.

[mecanicman]

I believe your current o/s is looking for input from the refrigerant pressure sensor. From looking the wiring diagrams it looks like you may have better luck running an express van file, but I have not tried it.

[6speedblazer]

But shouldnt the inputs required change when the file is switched from serial to analog. Seems silly for the os to still be expecting a pressure sensor input when i can swap to analog control.

[6speedblazer]

Finally tried an express van tune. Ac works flawlessly. So conclusion is that a silvy OS wont support analog cylcing.

[LSxpwrdZ]

Or just segment swap the system segment from the express van file... There are still things in there going on that we can't edit to fully turn on the analog AC on the P59 PCM's. Segment swapping the system segment or using the entire express van file is the only way currently.

[6speedblazer]

I might have to look into a segment swap. The express van file changed the VIN in the pcm. The silverado tune kept my s10 vin in the pcm.

[LSxpwrdZ]

If you need help with that shoot me an email. [email protected]

[6speedblazer]

If you need help with that shoot me an email. [email protected]

i appreciate the help.

I just tried swapping the Express van system segment into the silverado file. AC still wont work. I can see that its being requested in the PCM but it will never switch on. I can drop the Express van file back in and it works perfectly.

All in all its not a huge issue as everything seems to work fine with the van tune.

Interesting note, the PCM reads as a 2003 s10 with my vin as it should. Maybe i made up that part about the VIN changing with the van tune.