[beking32]

Hello everyone, I’m trying to connect my ac. I have a 411 pcm from psi with standalone harness. I kept all factory ac system and wiring. My problem is that it’s not getting ground to relay. I tried bypassing the high pressure sensor, replacing high pressure sensor. No luck. I check all wiring. With a scan tool I can command ac to cycle only when key on engine off. If I try with engine on it’s says ac pressure incorrect. Seem like my pcm is not reading pressure from high pressure sensor. I was looking for a binary or trinary switch but cant find any that fit. If anyone can help it will be great.

 

[95wagon]

I think it is looking for the 3 wire pressure transducer .

What year car is this in?

 

[Fred Kiehl]

I have a 91 OCC, and the AC is pretty much a stand alone system with no input from my Holley MPFI on the 454. The only thing that is at all interconnected is the fans, and they are operated by the computer according to water temp.

 

[beking32]

I think it is looking for the 3 wire pressure transducer .

What year car is this in?

96 impala the factory high pressure switch is 3 wire

 

[beking32]

I have a 91 OCC, and the AC is pretty much a stand alone system with no input from my Holley MPFI on the 454. The only thing that is at all interconnected is the fans, and they are operated by the computer according to water temp.

Are you using a trinary switch?

 

[Fix Until Broke]

I don't think the 3 wire device is a switch - it's a sensor that has +5v power, ground and a 0.5v-4.5v voltage output signal that is linear with pressure on the sensor. The ECU reads this voltage from the sensor and then decides what to do with the fans, clutch, HVAC, etc

 

[95wagon]

That is a pressure transducer on your 96
yes is how the pcm determines high pressure ( and every other pressure 🙂) but it is not a switch.

411 should be perfectly happy to work with it.
Look at the lt1 torque head system, it uses a 411

I have an E67 which presents unique issues as there was never a calibration that both a manual trans and non data control.

I have something in the works but currently use a trinary.
Trinary switches when you have an ECM capable of proper control is a side steping corner cut.

 

[beking32]

Sorry

I don't think the 3 wire device is a switch - it's a sensor that has +5v power, ground and a 0.5v-4.5v voltage output signal that is linear with pressure on the sensor. The ECU reads this voltage from the sensor and then decides what to do with the fans, clutch, HVAC, etc

sorry I mean sensor. It’s a factory sensor. So you basically saying bad pcm? I understand torque head uses the same 411.

 

[Fix Until Broke]

I'm not saying anything is bad yet - not enough info to come to that conclusion.

You replaced the sensor - are you getting a reasonable reading (in volts) back to the PCM?
You tried bypassing the sensor - Any details on how this was done?
Is the system charged correctly?
Is the low side switch functioning properly?

 

[beking32]

I'm not saying anything is bad yet - not enough info to come to that conclusion.

You replaced the sensor - are you getting a reasonable reading (in volts) back to the PCM?
You tried bypassing the sensor - Any details on how this was done?
Is the system charged correctly?
Is the low side switch functioning properly?

Grey to blue 45 4.5 volts
Black to blue 60- good
Red to red 14- not sure of the number
System is fully charged 2 1/2 cans; installed with guage. I had to jump pin 43 to ground to get the Freon in.
Low switch I believe is ok. I’m getting ac request on scanner. Fuse is good. I bypassed well tried to bypass sensor by using 80k resistor between pin blue 45 and red14.

 

[beking32]

Grey to blue 45 4.5 volts
Black to blue 60- good
Red to red 14- not sure of the number
System is fully charged 2 1/2 cans; installed with guage. I had to jump pin 43 to ground to get the Freon in.
Low switch I believe is ok. I’m getting ac request on scanner. Fuse is good. I bypassed well tried to bypass sensor by using 80k resistor between pin blue 45 and red14.

The red wire did have power though

 

[beking32]

I have a 91 OCC, and the AC is pretty much a stand alone system with no input from my Holley MPFI on the 454. The only thing that is at all interconnected is the fans, and they are operated by the computer according to water temp.

That maybe an option for me if I can’t do it the right way. (Control by pcm)

 

[beking32]

I'm not saying anything is bad yet - not enough info to come to that conclusion.

You replaced the sensor - are you getting a reasonable reading (in volts) back to the PCM?
You tried bypassing the sensor - Any details on how this was done?
Is the system charged correctly?
Is the low side switch functioning properly?

Also will using aluminum wiring with copper a bad thing to do?

 

[Fix Until Broke]

Grey to blue 45 4.5 volts
Black to blue 60- good
Red to red 14- not sure of the number
System is fully charged 2 1/2 cans; installed with guage. I had to jump pin 43 to ground to get the Freon in.
Low switch I believe is ok. I’m getting ac request on scanner. Fuse is good. I bypassed well tried to bypass sensor by using 80k resistor between pin blue 45 and red14.

Maybe Impala has different colors than Roadmaster (both 96)...? A/B/C will be the same on the sensor, regardless of the colors (or numbers?). Can you explain what the numbers 45, 60, 14, 43, etc mean?
A = Ground
B = +5v relative to ground
C = 0.5v (relative to ground) at 0 pressure and 4.5v at max pressure (guessing ~400 psi?)

C should read 1.5-2.0-ish volts with the compressor not running

 

[beking32]

Maybe Impala has different colors than Roadmaster (both 96)...? A/B/C will be the same on the sensor, regardless of the colors (or numbers?). Can you explain what the numbers 45, 60, 14, 43, etc mean?
A = Ground
B = +5v relative to ground
C = 0.5v (relative to ground) at 0 pressure and 4.5v at max pressure (guessing ~400 psi?)

C should read 1.5-2.0-ish volts with the compressor not running

View attachment 206026

I’m using 411 red blue pcm.
45 blue is 5 volt ref.
Blue 60 is ground
Red 14 is pressure signal
These numbers are for the high pressure sensor to pcm
Red 43 is ac relay control
I will check the voltage again tomorrow

 

[95wagon]

What is your calibration based on?

Maybe the cal is looking for something that is not there .
Or the wirring is different.

 

[95wagon]

Saw the other thread you were posting in.
The ground from sensor must go to PMC ref ground .
I believe tieing it to any chassis or engine grounds could get you into trouble as any loads could skew things.
The pcm sensor ref voltage is relative the pcm ref ground . Anything else other than sensors on that ground line could make the PCM " see" a sensor voltage return other than the voltage the sensor is outputting

 

[Fix Until Broke]

I’m using 411 red blue pcm.
45 blue is 5 volt ref.
Blue 60 is ground
Red 14 is pressure signal
These numbers are for the high pressure sensor to pcm
Red 43 is ac relay control
I will check the voltage again tomorrow

Got it - Thansk for the clarification. You mentioned that in the original post and I didn't consider that.

Regardless of the numbers/colors - A/B/C on the sensor need to be correct as noted above. The connector will have those letters molded in.

 

[beking32]

What is your calibration based on?

Maybe the cal is looking for something that is not there .
Or the wirring is different.

Not sure. Scanner says 2000 Chevy truck. I will check wiring today. Going by what brother fix until broke said, the wires may be crossed. I matched the colors but that maybe wrong. We will see. Fingers crossed

 

[buickman1]

Also will using aluminum wiring with copper a bad thing to do?

You can use aluminum and copper together. It is common in building wiring, but you shoud use noalox, as copper and aluminum together with electricity create an electrolysis effect, that will corrode the wires at different rates. You can get it at home depot or lowes.