2004 Chevy Diesel Dual Heater Control Problem

[chasdvorak]

Hello....I hope I'm in the right place. I'm looking for some help with my truck heating system. I have a 2004 Chevy Silverado 2500HD with a dual control (digital display) heater/ac module. The heat will not turn on until I set the temperature to 90 degrees (max setting). If I drop it down to 89 degrees, I get cold air.

I checked the fluid level, tried disconnecting both batteries, checked all fuses, no codes listed and I even hopped on one foot. I checked some truck forums and they discussed everything from replacing actuators, temperature control sensors and the temperature control unit.....$$$$.

The blower seems to work normally and the vent doors appear to be working properly so I don't think its tied into something mechanical. I'm hoping it's an easy fix, but wanted to get some advice before I take it in to the shop.

Thanks in advance,

Chuck Dvorak

 

[GOTTOYS]

Sounds to me like a problem with the heater/ac control head. A dealer should be able to perform a scan on it and that will point them toward the problem. Don't just start throwing parts at it, this can get expensive and probably won't fix it. I would recommend a competent GM dealer at least for the diagnosis. They will have the right equipment, manuals and knowledge to figure it out. My guess is they could locate the problem in about 1 hour or less, that may not include fixing it and that is just a guess. Your results may vary. Around here our dealer labor rates are around $100/hr. Maybe a little more usually with a 1 hour minimum for diagnostic work. Those automatic temperature controls are nice but when they quit they can be expensive. If that's what it needs you may be able to find a used or remanufactured unit. I wouldn't expect a dealer to replace it with anything less than a new one. They have to warranty their work and won't if the part isn't new. Good luck...Don

 

[Bob&Patty]

Chuck, I think that you have the "auto" A/C control by what you discribed. Now with the "auto" air there are 2 "temp door" actuators....drivers and passengers. Does the heat still blow out the bottom?? Does either side have warm air at a "normal" setting?? The "temp door" actuators can go bad......or 1 can stick....but both at the same time...not likely. Just so you know, 90* is an override so you can get heat. Also, the inside air temp asperator located in the headliner ( it's not a radio speaker) above the drivers seat could be the problem. Has it made any strange noises lately?? BTW, if it's COLD in the AM the heater wont come on until the engine temp reaches 100*. This is all an educated guess and some knowledge on GM vehicles.

 

[chasdvorak]

Hey Bob,

Thanks for the help. I do have the auto feature...I think the temp actuators are functioning since it works the same on both sides.......no heat until 90 degrees and it doesn't make a difference if I move it from floor to vent to defrost. I read some posts about the asperator and located it....thought it was part of the OnStar, but it has not been making any noises. Any way to test that part? I'm was hoping to rule that out before taking it in to the dealer or before buying a new control unit. Thanks in advance for your helo.

Chuck

 

[chasdvorak]

I forgot to mention the warm up....this happens consistently when I drive for 10 minutes or hours. The temp gauge is reading the normal hot range, but that 90 degree over-ride is the only way to get heat. any tips for getting to the asperator without trashing the trim or headliner? Thanks again.

Chuck

 

[Bob&Patty]

Chuck, to get to the asperator....you have to remove the sunshade and the left "A" pillar trim. The sunshade has "torx" screws and the "A" pillar just pulls off...sorta. Be carefull removing it and only pull it far enough to unplug the speaker if you have the "bozo" radio. You can pull the headliner down enough to see it. You remove the cover...carefully.....(looks like a speaker cover) to remove it. To test the asperator you would need a DOM meter and have to know what the values are from GM.

I'm still a little confused. It sounds like the "MODE" door actuators are working properly.....the A/C, heater, and defrosters. It's just the tempurature part that is not working........no heat and is it just one side or both sides ?? How about the A/C does it blow cold..then warm up a little if you have it set at..lets say you run it from 60* to 74* ?? BTW, does to outside temp reading work??

Just a thought.......could the "heater core" be plugged?? It happens and you will not get heat until you rev the engine and hold it at any temp setting.

 

[chasdvorak]

Bob,

Thanks for the help...I appreciate you continued help. I believe the Mode doors are working properly. They function correctly and I can hear them move while the air shifts from floor, defrost, vents. It's just the heat on both sides. Set one, the other or both to 90 degrees and you have heat....drop it to 89 and you have cold as you move it anywhere below 90 degrees. I can set one side to 90 degrees and I have hot while the other is set at 89 or lower and its' cold (or vice versa). The outside temperature is reading correctly and I don't have to jump on it to get the heat....gauge temp and warm-up appear normal. The truck is garaged and I have heat a few minutes after driving it in the 35-40 mph range. I didn't notice any ac problems, but will try to see if it gets warmer in the 60-74 range. I took a quick check of the fuses and found no problems. I purchased the truck used with 42,000 miles (2 years ago) and had the cooling system flushed and transmission oil changed... been keeping up with the routine maintenance. I'm willing to take a shot at replacing the panel or asperator (never heard any buzzing or clicking sounds) but was hoping to save the diagnostics fee if I could somewhat limit the components....I know there are no guarantees....unless I pay the pros, but do appreciate the advice.

Chuck

 

[Bob&Patty]

Chuck, let me make a phone call. I will try to get back to you on Monday. I'm going to call the Chevy dealer I worked at. I worked on lots of A/C / heater problems.....but have never had both sides take a dive at the same time. Might be in the control head. Their not cheap and being an electronic part you can't return it if it does not fix the problem. Hang in there and let me see what I can find out. BTW, send me a PM with your PH# and I will call you instead of typing all this stuff.

 

[Bigwhitetruck]

Chuck,

I am having the exact same problem with my 2004 Chevy Silverado 2500. My heat only works when it is on 90 degrees. I turn it to 89 degrees and it gets cold. Hope you was able to solve your issue and can pass the info on to me. Thanks in advance

 

[danemayer]

This thread is from 2010.

 

[cookie]

The OP, Chuck, has not been on the forum for the past two years. I think he is no longer a Heartland owner.

Peace
Dave