Spoke to soon. When I installed the HVAC I just tested the blower and it worked fine. Today after driving the Blazer the heat selector is on full hot and the air position selector does not function.
What a hassle. Contacting the seller...
JM

 

I put the new controller on today and the HVAC is acting the same as the previous one. The original HVAC was completely dead. The last two used HVAC units I put on have acted the same way. The blower selector works fine but the other two controllers do not. The heat selector does not change the temp and the position selector that determines where the air is distributed does not work.

Is there a computer that needs to be reset with the new unit?

Any thoughts on the next move?

Thank you,
John

 

I have a couple of thoughts. First is you might need to force a recalibration of the actuator positioning. The procedure is to turn the ignition off, leave the battery connected and the remove the HVAC fuse for 60 seconds and reinstall. The procedure does not say which fuse since there is more than one so try them each in sequence (one out then back in then move on to the next one). If that does not work then you may have a sensor failure which forces a default mode until repaired. Lets try the fuse trick first.


George

 

Sounds good.

 

Hello George,

I reset all circuit breakers involved as you mentioned. No change. To be more accurate. The heat selector acts as follows. Blows hot air in all positions except when the **** is in the red detent all the way to the right. The air position indicator made some noise when first turning on the key after the reset but then stopped and the primary air position is blowing from the vents in the dash. No change when moving the position indicator.

I wonder if GM has a sequence when putting in a different controller.

What would cause the original controller to fail. When smelling the original controller I do not smell any odd electrical oder.

Taking the car to the dealer could be a money suck...

Thank you again for taking the time to consider the problem.

JM

 

I'll get back to you tomorrow on this.


George

 

Thank you.

Yesterday I tried a reset again on the ECC. This time pulling the radio/batt fuse for 30 seconds and then turning the ignition on for 40 seconds before starting the car. I could hear a module possibly aligning once the key was on. Was a steady noise then intermittent. Still no luck. Was going to put a OBD2 scanner on today and see if it brings up any codes.

 

I have reviewed the factory service manual instructions in detail. The starting point for almost all failures is code scanning. This is especially relevant to your auto HVAC system because many of the commands and inputs are transferred on the class 2 serial data bus with digital data transfers and a variety of fault codes can be stored but they are GM proprietary codes that will not be red by a garden variety scanner. Those codes can sometimes help to hone in on the issue.

The only step that you must perform after replacing the HVAC control module is the actuator recalibration that we have discussed. I figured out which fuse they are talking about, its the RDO/batt fuse #19 in the IPFB. Pull that for 30 seconds with the ignition off and everything else in the normal state.

The majority of the problems you are describing are controlled by the solenoid assembly. Make sure that the connections are all good.

The only other thing that I know of are the sensors that input into the hvac module. If one of them fails it can force a default setting that may prevent changes to the controller positions. That would require testing of the sensor values under known conditions. Let me know if you want to go there.

George

 

Here's what I went through to get the ECC working on my (newly acquired) '99 LT in June of 2020. The ECC was acting totally flaky. Usually it blew hot or warm all the time, out of the dash vents. The refrigeration system was working fine, and I thought it was OK when I test drove it a month earlier. So I was quite puzzled.

1. The blend door actuator turned out to be one of the early originals. I know that because of the p/n that was on it. And, just like all the originals, the big actuator gear was split causing it to slip on the shaft. How that part never got changed in 21 years is beyond my understanding.
   * But the system still didn't work correctly after the actuator change.
2. Next I found a leaking vacuum hose and a leaking vacuum reservoir. New reservoirs aren't available, so I made one out of a #2 tin can, and replaced ALL the vacuum hoses. And when I finished ... although it seemed better, it still wasn't working right.
3. After checking the electrical circuits and the vacuum actuators in the dash as best I could, the only thing left was the control module. I spent alot of time searching the internet for a new one. They're no longer available from GM, and Dorman doesn't even list the Blazer p/n anymore. But by some miracle I located a NOS (new old stock) unit at a Chevy dealer in Puerto Rico! And I paid through the nose for it! Just a few bucks shy of $500!
4. Thankfully, that new module did the trick, and the system now works like it should. But . . .

The control module fixed it because the one I took out was a Dorman rebuilt with the wrong part number (599-260). So someone in the past threw a (wrong) control module at it without checking for the most common failures first, ie. if the blend door actuator had been replaced when it should have, all I would have had to do was fix the vacuum leaks.

 

Hello Red,
Thank you for the info. Do you remember the part number on the climate control? Was it 09356175?

JM