1990 HVAC Control Flashing

[EDS_5_OH]

All,

My son recently purchased a 1990 K1500 RCSB. We are working through some of the little problems with it and we can't seem to figure this one out. The HVAC control panel works fine when you start the truck for about 2 minutes. After 2 minutes, the air deflector location display starts flashing arrows at all locations. Shortly after, the temperature display starts flashing arrows at all locations. I verified that the air deflector damper moves to all positions, even works while the indicator is flashing. I verified that the heater damper moves from hot to cold and back, even while the arrows are flashing.

In a box of parts than came with the truck was a spare HVAC controller from a 94 GMC Sierra. I swapped this unit in and it acts the same. The unit installed in the truck has a 4/2011 build date on it, apparently a replacement.

Any thoughts on what to check next?

Thanks,
Ed

 

[someotherguy]

It's been many years since I had to troubleshoot flashing arrows on the 1988-1994 A/C controls, but I do believe that although you saw the actuators go through their motions, you have problems with them. I don't think I've seen both the vent position AND temperature mix arrows flash, though. I have repaired one truck where the temperature arrows would flash; the actuator was bad.

Richard

 

[skylark]

I recall low pressure in the A/C causing a display issue on the early trucks but it has been so long that I don't recall if there were arrows involved.

 

[someotherguy]

Low refrigerant charge will start the actual "A/C" icon flashing and disable the compressor until you either disconnect the battery, or the controls, to clear the error condition. It will then short-cycle a number of times before it decides it's happening too often again and will set the error code (internal to the controls, not an ECM error) and start flashing A/C again.

Richard

 

[skylark]

Low refrigerant charge will start the actual "A/C" icon flashing and disable the compressor until you either disconnect the battery, or the controls, to clear the error condition. It will then short-cycle a number of times before it decides it's happening too often again and will set the error code (internal to the controls, not an ECM error) and start flashing A/C again.

Richard

Once again you are correct!

 

[EDS_5_OH]

It's been many years since I had to troubleshoot flashing arrows on the 1988-1994 A/C controls, but I do believe that although you saw the actuators go through their motions, you have problems with them. I don't think I've seen both the vent position AND temperature mix arrows flash, though. I have repaired one truck where the temperature arrows would flash; the actuator was bad.

Richard

Do you think the actuators are just sticky? Maybe I can remove the actuators and clean them up a bit? This truck has 95k original miles so it has sat quite a lot over the years.

The linkages on the damper look clean and looked like they were moving smoothly, we can spray some lubricant on them to see if it helps.

Since both the damper location and the temperature location arrows are flashing, should I be looking to replace both?

Also, both controllers are identical so they are from the newer series truck (93-94?) and have the MAX button. Are these interchangeable with the older series units?

Thanks for the help so far,
Ed

One more question. Where is the best place to purchase replacement actuators?

 

[someotherguy]

I'd gamble a couple bucks on anoher temperature mix actuator from the boneyard just to see if it changes anything. That particular actuator doesn't often go bad, so it would be an inexpensive way to rule it out. New actuators are kinda pricey.

Richard

 

[EDS_5_OH]

I've replaced both actuators, the temperature blender and the air diverter door. Both make full ranges of motion and both work flawlessly for several minutes. Eventually, the display begins flashing again. Oddly, even when flashing, both actuators move to required positions.

The control unit in the truck when we bought it is clearly a remanufactured unit from a new truck (93-94). The additional salvage yard unit that came with the truck is from a 1994 GMC Sierra (build date sticker on it). I wonder if the issue is that my truck is a 1990 and it possibly came with the unit that does not have the recirc or max button. Any thoughts on buying a simplified remanufactured unit without the Max or Recirc button? Short of tracing each wire back to it's source, I'm at a loss.

 

[EDS_5_OH]

To possibly help others, we replaced the control unit with one without the MAX or RECIRC button and the problem is solved.

 

[natedogg024]

I have a couple questions for clarification.
Some background:
I just got my interior all together and my engine started. I have a mix of to different years going on. My cab is a 1990 Z71 which I did not touch the HVAC system at all. I removed all the interior and replaced it with my 1993 interior. I swapped everything, dash board, wire harness, radio, and so on (with the exception of the HVAC system from '93). After hooking up power and starting the truck, I noticed I'm having the same issue as you described. I have the controller from '93 trying to control the '90 HVAC system.

I don't recall what the controller from the '90 looked like, or its functions compared to the 93, but you said in your last post that by installing a '90 controller the problem was salved? Could you help me out and explain what the "RECIRC" button is.

I should also mention I have not finished installing any of the A/C components under the hood. Everything is out and open, not hooked up. Did you check any of that stuff as mentioned in this thread before changing the controller?

Thanks
Nate