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clinebarger · 09-13-2016, 08:59 PM

This thread was dead anyway.....Doesn't bother me at all Rob.

It is NOT a Trinary, The Transducer sends a 0-5vdc signal too the PCM & is read as Actual/Real Time A/C Head Pressure, The PCM will control the Fans per Pressure & disable them above a certain speed, You can change all these settings with HPT's.

A '05 GMT800 P59 is "Serial Cycling" from the factory, Meaning the HVAC Control head not only sends a Serial A/C Request, But can also send A/C Clutch Cycling Requests over the Serial Data Line as well (Low Pressure Cycling) because the Low Pressure Switch is wired to the Control Head not the PCM. High Pressure Cut-Out is based on Transducer Readings.

The thread you linked too mentions Van PCM's, They are Analog Cycling, The Control Head sends a 12vdc A/C Request, A simple High Pressure cut out switch is wired inline & interrupts the Request if pressure is too high. The Low Pressure Switch is wired to the PCM directly.

Analog.....Was used on 4th gen F-Bodies, No Low Pressure Switches as the Compressors are a Variable Design, PCM can turn the Compressor off is Transducer/AC Head Pressure is too high.

Serial.....Corvettes, CTS-V etc.

All the above "Settings/Type Fitted" cannot be actually changed with HPT's, It's Hardware......Tuning Software has no effect.

The ONLY PCM I know of that accepts a 12vdc A/C Request & Control the Fans via Transducer input is "0411" PCM's from '99-'02 F-Bodies But those won't work with our DBW set-up.

Unless John Spears has figured out how too do this with a GMT800 P59 PCM, The 12vdc you have on the A/C Request wire will not prompt the PCM too ground your Compressor Clutch Relay (Did John flash your PCM?)

Back to the Van P59's, They do accept a 12vdc A/C Request, And will ground the A/C Clutch Relay (With the Low Pressure Input grounded), But WILL NOT operate the Fans per Transducer Input!

'03 & '04 GMT800 P59's do not accept a 12vdc A/C Request nor will they Operate the Fans per Pressure.

'05, '06, & '07 Classic GMT P59's do not accept a 12vdc Request, But WILL operate the Fans per Pressure.

09-13-2016, 08:59 PM	#45
clinebarger Senior Member Join Date: May 2009 Location: Fort Worth, TX Posts: 6,370	Re: Need some help with tuning. This thread was dead anyway.....Doesn't bother me at all Rob. It is NOT a Trinary, The Transducer sends a 0-5vdc signal too the PCM & is read as Actual/Real Time A/C Head Pressure, The PCM will control the Fans per Pressure & disable them above a certain speed, You can change all these settings with HPT's. A '05 GMT800 P59 is "Serial Cycling" from the factory, Meaning the HVAC Control head not only sends a Serial A/C Request, But can also send A/C Clutch Cycling Requests over the Serial Data Line as well (Low Pressure Cycling) because the Low Pressure Switch is wired to the Control Head not the PCM. High Pressure Cut-Out is based on Transducer Readings. The thread you linked too mentions Van PCM's, They are Analog Cycling, The Control Head sends a 12vdc A/C Request, A simple High Pressure cut out switch is wired inline & interrupts the Request if pressure is too high. The Low Pressure Switch is wired to the PCM directly. Analog.....Was used on 4th gen F-Bodies, No Low Pressure Switches as the Compressors are a Variable Design, PCM can turn the Compressor off is Transducer/AC Head Pressure is too high. Serial.....Corvettes, CTS-V etc. All the above "Settings/Type Fitted" cannot be actually changed with HPT's, It's Hardware......Tuning Software has no effect. The ONLY PCM I know of that accepts a 12vdc A/C Request & Control the Fans via Transducer input is "0411" PCM's from '99-'02 F-Bodies But those won't work with our DBW set-up. Unless John Spears has figured out how too do this with a GMT800 P59 PCM, The 12vdc you have on the A/C Request wire will not prompt the PCM too ground your Compressor Clutch Relay (Did John flash your PCM?) Back to the Van P59's, They do accept a 12vdc A/C Request, And will ground the A/C Clutch Relay (With the Low Pressure Input grounded), But WILL NOT operate the Fans per Transducer Input! '03 & '04 GMT800 P59's do not accept a 12vdc A/C Request nor will they Operate the Fans per Pressure. '05, '06, & '07 Classic GMT P59's do not accept a 12vdc Request, But WILL operate the Fans per Pressure.