My Hummer Problems

[Humvdood]

Okay, I'm a seasoned mechanic as I've said in other posts.
I've been doing this my whole life and know little about anything other than cars.
I've been having issues with this hummer since day one and brought in 2 other mechanics - my friendly competitors - but we are all at a loss.
I'm kind of just throwing all of this out there to see if anyone has any ideas or has had similar issues that they've been able to resolve.

My air compressor does not engage.
We hooked up a tech 2 to it and the pressure switch is only reading 0.92 volts when it should be reading 5 volts.
We replaced the pressure switch and it's still reading the same.
I can force it on with the tech 2 but I really don't want to drive around with a $4,000 tool connected to my obd port just so I can turn on my a/c.
We put a vacuum pump on it and evacuated everything just to make sure there wasn't any air in the system and have it fully charged with brand new freon - some electrical issue is keeping it from turning on but we can't figure it out.

My Cruise Control does not work.
The tech 2 tool isn't showing me any reasons why it should not work but it isn't.
Relays and fuses related to cruise control have all been swapped with brand new components.

My DIC and OnStar mirror temp and compass do not light up.

I'm thinking this could all be related but with this multiplex ignition system we are having a really hard time pinpointing anything at all.

 

[SuperBuickGuy]

the pressure switch is a wear item (unfortunately)... a friend of mine who owns a shop insisted I replace the pressure switch when I did other work on my system because he makes good money replacing them when they fail

cruise control relies on several "yes" boxes being checked before engaging - such as "is the vehicle in gear" "is the brake pedal engaged" - so you can have no fault in the system, but a subsystem fault would prevent it from operating - look at its criteria then troubleshoot those... such as a faulty brake switch (and, IIRC, the brake switch for the cruise control isn't the same one as for the lights)

 

[abearden]

Switch sounds like a bad supply voltage or ground.

 

[Humvdood]

Yeah we replaced the switch first thing.
See, what started this all was the previous owner had attempted to repair a burnt up blower motor resistor using butt connectors and RadioShack resistors but something shorted out and it fried everything from the HVAC controls to the bcm. I got the car for a pretty good price cause the owner was tired of dealing with it. Bcm is fine and pretty much everything in the system is new. It's just not getting the voltage it needs to turn on the compressor. I thought maybe the PCM was crap because the cruise control isn't working but it's communicating with the scanner... I would say this is making me look bad but considering it's got 2 other master mechanics stumped I'm gonna blame the design on this one.

 

[Renagade132]

I know it sounds silly, but maybe try switching the pressure switch again, sometimes even new out of the box can be bad also.

 

[4speedfunk]

H3's are famous for faulty brake light switches. Mine was replaced at only 2000 miles. Cruise control will not work and you'll get a host of crazy problems including the entire vehicle slowing to a complete stop with the throttle full open. It's located somewhere on the column by the pedals.

Not sure if this has any bearing on the AC but a bad brake light switch will kill the CC for sure. Worth looking at simply due to the numerous stories I've heard.

Obviously, you've figured this out by now...the H3 is an electronic nightmare. It will test even the most experienced mechanic.

 

[Humvdood]

H3's are famous for faulty brake light switches. Mine was replaced at only 2000 miles. Cruise control will not work and you'll get a host of crazy problems including the entire vehicle slowing to a complete stop with the throttle full open. It's located somewhere on the column by the pedals.

Not sure if this has any bearing on the AC but a bad brake light switch will kill the CC for sure. Worth looking at simply due to the numerous stories I've heard.

Obviously, you've figured this out by now...the H3 is an electronic nightmare. It will test even the most experienced mechanic.

God, I hate the ignition/passlock on this thing. I bought the H3 with the thought, "hey, I've only worked on a couple of these for minor issues - they must be pretty solid." No... It's because they are diagnostic nightmares. If I ever get one in my shop I'm charging the "pain in the @$$" fees for sure.

I'll swap out the brake switch cause now that I think about it, the previous owner had tried installing a dvd player and instead of hooking the ground up to the parking brake he had it hooked up to one of the brake wires. It didn't even cross my mind that he hay have grounded it out on a positive wire and fried part of the switch - or at least the part for CC.

 

[Humvdood]

Well, I took it to a chevy dealership. None of my friends work for dealerships so I thought I'd have to pay for diagnostics but they pulled me back there with them. I showed them everything I had done and we still couldn't get it figured out. They went to the parts dept and got a new switch and tried it out... same thing. I've still got my money but no a/c and I owe my competition all over town favors.
It's no biggy right now because the weather isn't hot but come summer I may just have to install a jumper switch to rig it up if I don't get it figured out.

 

[citiboy]

My air compressor does not engage.
We hooked up a tech 2 to it and the pressure switch is only reading 0.92 volts when it should be reading 5 volts.
We replaced the pressure switch and it's still reading the same.
I can force it on with the tech 2 but I really don't want to drive around with a $4,000 tool connected to my obd port just so I can turn on my a/c.
We put a vacuum pump on it and evacuated everything just to make sure there wasn't any air in the system and have it fully charged with brand new freon - some electrical issue is keeping it from turning on but we can't figure it out.

Did you happen to check the ac refrigerant pressure in the system?

From the service manual.

The A/C refrigerant pressure sensor is a 3-wire piezoelectric pressure transducer. A 5-volt reference, low reference, and signal circuits enable the sensor to operate. The A/C pressure signal can be between 0-5 volts. When the A/C refrigerant pressure is low, the signal value is near 0 volts. When the A/C refrigerant pressure is high, the signal value is near 5 volts.

The A/C refrigerant pressure sensor protects the A/C system from operating when an excessively high or low pressure condition exists. The powertrain control module (PCM) disables the compressor clutch under the following conditions:

A/C pressure is more than 2,951 kPa (428 psi). The clutch will be enabled after the pressure decreases to less than 2,068 kPa (300 psi). A/C high side pressure is less than 310 kPa (44 psi). The clutch will be enabled after the A/C high side pressure increases to more than 310 kPa (44 psi).

 

[citiboy]

Here's more info that may help in troubleshooting. Goodluck.

Heating and A/C Operation

The purpose of the heating and A/C system is to provide heated and cooled air to the interior of the vehicle. The A/C system will also remove humidity from the interior and reduce windshield fogging. The vehicle operator can determine the passenger compartment temperature by adjusting the air temperature switch. Regardless of the temperature setting, the following can effect the rate that the HVAC system can achieve the desired temperature:
• Recirculation
• Difference between inside and desired temperature
• Difference between ambient and desired temperature
• Blower motor speed setting
• Mode setting

The vehicle operator can activate the A/C system by pressing the A/C switch. The A/C system can operate regardless of the air temperature or mode setting. When the A/C switch is pressed, the HVAC control assembly applies 10 volts to the A/C request signal circuit. The voltage is then sent through the evaporator temperature sensor, if the evaporator temperature is above 0°C (32°F), then the voltage is applied to the other A/C request signal circuit to the BCM. The BCM receives the voltage input and sends a class 2 message to the PCM for an A/C request.

The PCM will operate the A/C system automatically in FRONT DEFROST mode to help reduce moisture inside the vehicle. The A/C LED will not illuminate unless the driver presses the A/C request switch on the HVAC control assembly. The A/C system maybe running without the A/C LED indicator illuminated when in FRONT DEFROST mode or Recirc. The following conditions must be met in order for the PCM to turn on the compressor clutch:
• BCM
- Battery voltage is between 9-16 volts.
- A/C request from the HVAC control assembly
• PCM
- Engine coolant temperature (ECT) is less than 123°C (253°F).
- Engine speed is less than 5300 RPM.
- Engine speed is more than 600 RPM.
- A/C high side pressure is between 2951-310 kPa (428-44 psi).

Once engaged, the compressor clutch will be disengaged for the following conditions:
• Throttle position is 100 percent for 10 seconds.
• A/C high side pressure is more than 2951 kPa (428 psi) and will re-engage once the pressure drops below 2068 kPa (300 psi).
• A/C high side pressure is less than 310 kPa (44 psi).
• Evaporator temperature is less than 0°C (32°F)
• Engine coolant temperature (ECT) is more than 123°C (253°F).
• Engine speed is less than 475 RPM.
• Engine speed is more than 6000 RPM.
• PCM detects excessive torque load.
• PCM detects insufficient idle quality.
• If the blower is switched to off.

When the compressor clutch disengages, the compressor clutch diode protects the electrical system from a voltage spike.

 

[Humvdood]

Here's more info that may help in troubleshooting. Goodluck.

Heating and A/C Operation

The purpose of the heating and A/C system is to provide heated and cooled air to the interior of the vehicle. The A/C system will also remove humidity from the interior and reduce windshield fogging. The vehicle operator can determine the passenger compartment temperature by adjusting the air temperature switch. Regardless of the temperature setting, the following can effect the rate that the HVAC system can achieve the desired temperature:
• Recirculation
• Difference between inside and desired temperature
• Difference between ambient and desired temperature
• Blower motor speed setting
• Mode setting

The vehicle operator can activate the A/C system by pressing the A/C switch. The A/C system can operate regardless of the air temperature or mode setting. When the A/C switch is pressed, the HVAC control assembly applies 10 volts to the A/C request signal circuit. The voltage is then sent through the evaporator temperature sensor, if the evaporator temperature is above 0°C (32°F), then the voltage is applied to the other A/C request signal circuit to the BCM. The BCM receives the voltage input and sends a class 2 message to the PCM for an A/C request.

The PCM will operate the A/C system automatically in FRONT DEFROST mode to help reduce moisture inside the vehicle. The A/C LED will not illuminate unless the driver presses the A/C request switch on the HVAC control assembly. The A/C system maybe running without the A/C LED indicator illuminated when in FRONT DEFROST mode or Recirc. The following conditions must be met in order for the PCM to turn on the compressor clutch:
• BCM
- Battery voltage is between 9-16 volts.
- A/C request from the HVAC control assembly
• PCM
- Engine coolant temperature (ECT) is less than 123°C (253°F).
- Engine speed is less than 5300 RPM.
- Engine speed is more than 600 RPM.
- A/C high side pressure is between 2951-310 kPa (428-44 psi).

Once engaged, the compressor clutch will be disengaged for the following conditions:
• Throttle position is 100 percent for 10 seconds.
• A/C high side pressure is more than 2951 kPa (428 psi) and will re-engage once the pressure drops below 2068 kPa (300 psi).
• A/C high side pressure is less than 310 kPa (44 psi).
• Evaporator temperature is less than 0°C (32°F)
• Engine coolant temperature (ECT) is more than 123°C (253°F).
• Engine speed is less than 475 RPM.
• Engine speed is more than 6000 RPM.
• PCM detects excessive torque load.
• PCM detects insufficient idle quality.
• If the blower is switched to off.

When the compressor clutch disengages, the compressor clutch diode protects the electrical system from a voltage spike.

Can you cite where you got this info? none of my tech documents have this

 

[citiboy]

It came directly from GM service manual for technicians. I still have access as i used to work for GM as a master tech and now works at Honda. Let me know if you need more info and help a fellow technician.

Or you can get this exact same copy for all GM cars and trucks.

http://kickass.so/gm-service-manual-v09-t6245120.html (if there's no seeders, just google GM Service Manual v09, find and download any working links).

Goodluck.

 

[Humvdood]

I don't have online access I just have the cds and a binder so I could make copies and that wasn't in anything I had.
The stuff I have on the H3 is mostly just chart diagrams saying to start here, if that's not the problem move here, if that's not the problem trying replacing... blah blah blah.
I needed the short and sweet version like that.
Surprised the dealership here didn't pull up the site but they were already going out of their way to help me out for free...

 

[Humvdood]

This is going to sound retarded but the documents I have show the pressure should be WAYYYY lower. Like 25-30 psi low and 105-175 high.
It's maintaining the pressure I have it at and there are no leaks - not even in the compressor when I jump it. I'm wondering where the hell all that freon went to get so low... all of the techs I've had look at this with me have all had the same info too. crazy. hopefully that'll be it but I've gotta finish my line up for the day before I can throw another can or two in there.

 

[SuperBuickGuy]

It came directly from GM service manual for technicians. I still have access as i used to work for GM as a master tech and now works at Honda. Let me know if you need more info and help a fellow technician.

Or you can get this exact same copy for all GM cars and trucks.

http://kickass.so/gm-service-manual-v09-t6245120.html (if there's no seeders, just google GM Service Manual v09, find and download any working links).

Goodluck.

Be careful of this link - it will install Voleran, a tracking/malware program on your computer if you download the link. It took me 1 1/2 hours to remove it from my computer this morning..

 

[citiboy]

Be careful of this link - it will install Voleran, a tracking/malware program on your computer if you download the link. It took me 1 1/2 hours to remove it from my computer this morning..

You have to click "download torrent" from the very top of the page and you have to have a torrent client, i'm using utorrent.

Here, i found a working torrent, unzip then just click the file and the torrent client will automatically download it.