Oh boy, hvac issues and oil pressure fluctuations

Denali n DOO

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May 22, 2012
5,596
Well this all started yesterday, a very hot day too. So I leave for a drive, turn a/c off after startup, I open windows and roof and go for a drive. I get into heavy traffic and I got no breeze so I close the windows and roof and turn on the a/c. All I get is hot air coming out, doesn't matter what mode, temp setting or fan setting only could get hot air. Now I notice the oil pressure sitting 2 marks to the left of center when idling and it goes 1 mark to the right of center during acceleration. I never noticed this before I always thought the needle stayed at center. Maybe not related to a/c. So I turn it off again and run some errands and come back and start it up, same thing, hot air only and nothing else. I got home and let it sit for a couple hours and go start it up, everything is fine, full temp control cold or hot any vent any fan speed. I go for another drive today and it doesn't seam right again, now the odd thing, when I shut the engine off, removed the key and opened the door to kill the radio, THE FAN BLOWER KEPT RUNNING, excuse my language but WTF is the deal with that? I turned the key back to run position and off again and it turned off. I started it up again and drove home started to get some cool air but now the fan doesn't adjust to any speed it just stays on low speed. I been looking through some hvac issues others are experiencing but which if not all accuators may be causing the problems. Should I try pulling a fuse to reset the system?
 

The_Roadie

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Nov 19, 2011
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Possibly the ignition switch. More likely the master dash area ground bolt at the bottom right side of the center radio stack. Any chance you've seen the picture I've posted a few times?
 

Denali n DOO

Original poster
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May 22, 2012
5,596
the roadie said:
Possibly the ignition switch. More likely the master dash area ground bolt at the bottom right side of the center radio stack. Any chance you've seen the picture I've posted a few times?

No I haven't seen the picture but I do recall you discussing that ground at some point in a thread. I read a few hvac threads but didn't find any similiar issues to mine. I'm going to look around and see if I can see that ground, check for bad connection.

I pulled that cover off and looked, where I was looking is a black connector that goes in near the floor, or am I looking for a simple terminal bolted to some frame area (like the G041 ground at rear pillar) ? What thread might that pic be on?

I found your pic and that was the plug I saw. I messed around with it but it made no difference. I pulled that fuse 39 and gonna wait a few minutes, and then if I recall correctly turn key to run and leave it there for a bit so it calibrates? then start it and see what it does?
 

Denali n DOO

Original poster
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May 22, 2012
5,596
Denali n DOO said:
I found your pic and that was the plug I saw. I messed around with it but it made no difference. I pulled that fuse 39 and gonna wait a few minutes, and then if I recall correctly turn key to run and leave it there for a bit so it calibrates? then start it and see what it does?

pulling fuse did nothing. Today it still has no fan speed, i can see the display increasing fan speed but doesn't actually change it. Then today I notice while driving the whole system goes off and on by itself. Again today after shutting the truck off the fan continues to run. I can't recall the last time I actually drove this truck without any issues. so with the hvac issue should I give in and go to Stealership or maybe a A/C shop? is it easy to test the ignition switch?
 

Denali n DOO

Original poster
Member
May 22, 2012
5,596
the roadie said:
Got a meter and know how to use it?

I do have a meter but I don't really know too much about it. I watched a few youtube videos, did some continuity tests. I can get someone over here tho that would know how to use it properly. The ignition switch was changed out by the dealer when they were throwing parts at it for my no crank issue (that ended up to be new starter). this is the meter I have.

I just read an article by mellis and I know how to get the switch out of the column.
 

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The_Roadie

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Nov 19, 2011
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Ignition switch problems are so intermittent and hard to catch in the act that it's almost not worth applying a meter to it. If it's been replaced, then I withdraw my recommendation to look at it.

Tighten the ground bolt I mentioned, then pull and reseat the connectors on the back of the HVAC control unit. If it continues to run on after the switch is off, it could be a coincidental failure of the speed control module. Measure the voltage at the blower motor using the meter with the ignition off.
 

Denali n DOO

Original poster
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May 22, 2012
5,596
the roadie said:
Ignition switch problems are so intermittent and hard to catch in the act that it's almost not worth applying a meter to it. If it's been replaced, then I withdraw my recommendation to look at it.

Tighten the ground bolt I mentioned, then pull and reseat the connectors on the back of the HVAC control unit. If it continues to run on after the switch is off, it could be a coincidental failure of the speed control module. Measure the voltage at the blower motor using the meter with the ignition off.

i checked the grounds and also no power at blower motor with ignition off. Right now with A/C on no blower at all. What about the speed control module you mentioned?
 

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Denali n DOO

Original poster
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May 22, 2012
5,596
the roadie said:
That's the part. Does it have 12V going to it on the 3-pin connector? Could be a simple blown fuse.

It shows 14.15v at that connector, while I was checking that the blower turned on and ran a bit and then turned off. That heat sink got hot fast.
 

Denali n DOO

Original poster
Member
May 22, 2012
5,596
the roadie said:
That's why it's designed to be in the air flow. If the function doesn't change when you wiggle the connector, I'd suspect the module. Wish it was a $10 unit instead of over $50.

I just started it up and the blower came on about medium blow, I tried to lower the speed and then increase the speed, it went to full blow and stayed there and wouldn't adjust. Nothing happened when wiggling the wires. I was not able to turn off the HVAC at all. This time again it kept running when I took the key out. So you would still suggest to swap out that module right? My wife has to drive it to work tomorrow, is it okay if I leave that module unplugged or maybe pull a fuse or two. I don't wanna put it all back together until I have that new module to put in. Thanks Roadie!
 

Denali n DOO

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May 22, 2012
5,596
Denali n DOO said:
I just started it up and the blower came on about medium blow, I tried to lower the speed and then increase the speed, it went to full blow and stayed there and wouldn't adjust. Nothing happened when wiggling the wires. I was not able to turn off the HVAC at all. This time again it kept running when I took the key out. So you would still suggest to swap out that module right? My wife has to drive it to work tomorrow, is it okay if I leave that module unplugged or maybe pull a fuse or two. I don't wanna put it all back together until I have that new module to put in. Thanks Roadie!

Should I pull fuse 39 until I get a module in tomorrow night?
 

Denali n DOO

Original poster
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May 22, 2012
5,596
Okay, I got the new part. Supposed to be new improved design. but nowhere near $50, more like $149.35 list and I paid $118.54 :hissyfit: . So I'm going to splice some wires and put it in. This design only has 1 plug that connects to both the blower and control head. It also has a different heat sink design. Should I disconnect the battery or pull any fuses before I start? Will a recalibration be needed after replacement? heres some pics of the new one.
 

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The_Roadie

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Nov 19, 2011
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Recalibration not necessary, but one will be forced anyway when you pull the HVAC control module memory fuse (rear #36 - HVAC-B). Also very important - pull front fuse #35 that feeds the blower only. I understand everything costs more in Canada, but where did you buy that thing? The heat sink looks a lot more professional.

Added: Those 19260762 modules are closer to $60 here.
 

Denali n DOO

Original poster
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May 22, 2012
5,596
the roadie said:
Recalibration not necessary, but one will be forced anyway when you pull the HVAC control module memory fuse (rear #36 - HVAC-B). Also very important - pull front fuse #35 that feeds the blower only. I understand everything costs more in Canada, but where did you buy that thing? The heat sink looks a lot more professional.

Added: Those 19260762 modules are closer to $60 here.

The dealership had one in stock and they gave me 10% off (big flippin deal!!!). I hate going to the dealership but I realized this morning that I'd much rather be standing at the parts counter than the service counter. If I had more time I'd look on the internet at some of the places I notice members buy their parts at.

I'll pull rear #36 and front #35 fuses before I start. I'll solder and shrink wrap the wire splices. I'll report the outcome later today when it's completed.

Thanks Roadie!
 

Denali n DOO

Original poster
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May 22, 2012
5,596
Okay so I just got finished installing the new improved Speed Control Module, soldered the splices and shrink wrapped them. I put the two fuses back in and started it up. All the HVAC funtions are now working properly, hot or cold, in between, auto, all fan speeds. Everything is back to normal. Another sucessful repair and I even got to use the multimeter this time! Thanks Roadie for your TIME and GUIDANCE to solve my HVAC issue, you're awesome :thumbsup: !

GMTNation Rocks :wootwoot::wootwoot: !!

On a side note, I found this yellow plug near the XM Module, does anyone know what it's for?
 

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Denali n DOO

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May 22, 2012
5,596
the roadie said:
Thanks for the kind words. Glad to help.

Yellow connectors are for air bags. That should go to the passenger side unit, I think. Your air bag diagnostic light isn't on?

That makes sense then, I bet that plug is for the side impact air bags, 1 of 2 options that I don't have on mine.
 

Denali n DOO

Original poster
Member
May 22, 2012
5,596
A lot of a/c questions lately. I just wanted to bring mine up again. I've read so many /ac threads my head is spinning...so since changing the blower speed control module, all erratic behavior stopped, except I still don't think I have control of the temperature whether in auto mode or reg mode. For example in auto I set temp to 15(max ac) and it blows cold, I increase to 16 and it still blows cold, I can increase temp all the way to 31 and it still blows cold. As soon as I dial 32 it goes into Max heat mode and blows super hot, drop to 31 again and it goes right to cold. I either have cold or hot but nothing in between. It's been hot 30+deg and that's how it's acted in the hot weather. This morning in the cooler weather 15 deg it seemed to act like normal? So should I be looking to change the ambient temp sensor by the rad, or checking the little fan thing in the B pillar? Is that pillar cover hard to get off n on around the black window rubbers, does the lower trim have to come off first?
 

Denali n DOO

Original poster
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May 22, 2012
5,596
the roadie said:
Does it display the expected OUTSIDE temperature on your control module?

Yes the display shows the outside temperature. The display changes to show the temperature your dialing but after adjustment the display goes back to outside temperature.
 

Denali n DOO

Original poster
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May 22, 2012
5,596
Denali n DOO said:
Yes the display shows the outside temperature. The display changes to show the temperature your dialing but after adjustment the display goes back to outside temperature.

So pull the panel and check the fan deal in the B pillar? Which sensor could cause my no temp control?
 

BRomanJr

Member
Dec 9, 2011
371
Denali n DOO said:
A lot of a/c questions lately. I just wanted to bring mine up again. I've read so many /ac threads my head is spinning...so since changing the blower speed control module, all erratic behavior stopped, except I still don't think I have control of the temperature whether in auto mode or reg mode. For example in auto I set temp to 15(max ac) and it blows cold, I increase to 16 and it still blows cold, I can increase temp all the way to 31 and it still blows cold. As soon as I dial 32 it goes into Max heat mode and blows super hot, drop to 31 again and it goes right to cold. I either have cold or hot but nothing in between. It's been hot 30+deg and that's how it's acted in the hot weather. This morning in the cooler weather 15 deg it seemed to act like normal? So should I be looking to change the ambient temp sensor by the rad, or checking the little fan thing in the B pillar? Is that pillar cover hard to get off n on around the black window rubbers, does the lower trim have to come off first?

The auto system works a bit different from the manual system.
On a manual system, the outlet air temps respond immediately to your changes in the controls, not so with the auto.

On the auto system, the air temps are dependent on the input of all the sensors and the control temp setting.
There are temp sensors in the air ducts, outside ambient temp sensor in front of the radiator, internal ambient sensor w/fan in the B pillar and Sunload sensors in the middle top of dash.

The control panel uses all sensor inputs and built-in logic to determine the correct mode and temperature.
It can take a minute to respond to changes you make at the control panel.

Both extremes of the temperature control settings bypasses the logic and puts the system into manual max air or manual full hot. If setting to a normal temp (center of range) results in air that never settles into the correct temp, then it could be your B pillar sensor, usually the Thermistor gets dirty and won't report correctly (usually air too cold) If the Ambient sensor fan spins too slowly or stops, then system will output air that is be too cold in the summer and too hot in the winter.

Check and clean your B pillar sensor, that will improve things, the cover comes off with a firm tug on the multiple spring clips and you only need to loosen the top to get at it. The door seals are not affected and don't need to be removed.

If still not working properly all of the components will need to be monitored for correct feedback and or operation. This would include checking all temp sensors for correct readings and all mode/temp servos for proper operation and even your A/C pressures and condenser/evaporator/heater core air flows.
 

Denali n DOO

Original poster
Member
May 22, 2012
5,596
BRomanJr said:
The auto system works a bit different from the manual system.
On a manual system, the outlet air temps respond immediately to your changes in the controls, not so with the auto.

On the auto system, the air temps are dependent on the input of all the sensors and the control temp setting.
There are temp sensors in the air ducts, outside ambient temp sensor in front of the radiator, internal ambient sensor w/fan in the B pillar and Sunload sensors in the middle top of dash.

The control panel uses all sensor inputs and built-in logic to determine the correct mode and temperature.
It can take a minute to respond to changes you make at the control panel.

Both extremes of the temperature control settings bypasses the logic and puts the system into manual max air or manual full hot. If setting to a normal temp (center of range) results in air that never settles into the correct temp, then it could be your B pillar sensor, usually the Thermistor gets dirty and won't report correctly (usually air too cold) If the Ambient sensor fan spins too slowly or stops, then system will output air that is be too cold in the summer and too hot in the winter.

Check and clean your B pillar sensor, that will improve things, the cover comes off with a firm tug on the multiple spring clips and you only need to loosen the top to get at it. The door seals are not affected and don't need to be removed.

If still not working properly all of the components will need to be monitored for correct feedback and or operation. This would include checking all temp sensors for correct readings and all mode/temp servos for proper operation and even your A/C pressures and condenser/evaporator/heater core air flows.

I'm gonna have a look tonight at that sensor in B pillar and see if that helps. Sounds like there are more sensors than I thought. Thanks for the input. I'll report back with what I find out.
 

Denali n DOO

Original poster
Member
May 22, 2012
5,596
Just to report in this thread too, I changed the ambient air temperature sensor and now have full control of temps again. And it only cost me $7.70 to fix.

Thanks.
 

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