1997 K2500 keeps burning up HVAC Control boards, the control unit in the dash. The first one quit, I replaced it, then 4 months later it burned up, now, I think it is going out again. I replaced the relay and added grounds to the firewall frame and engine. AC and heat work fine when it's working but what has happened each time is we smell smoke when starting it up then about a week later it quits working. Upon inspection, there is an obvious burned area on the circuit board on the last one. What gives? Is there a cure?
Why does my Suburban keep burning up HVAC control
- Thread starter another Todd
- Start date
Any added electrical accessories in the vehicle that are not OEM, and (b) where are you getting your HVAC parts from?
Rock Auto. Genuine AC Delco part. There has been no added accessories in the last 10 years.
I would strongly suspect there is something wrong with the blower motor. If this module controls the fan speed, then maybe the fan is running but taking too much current, maybe because of a faulty motor winding. The compressor clutch coil would be my other suspect, and it could even be that the flyback diode on that has blown. I couldn't tell you where that diode is, but I thought it odd that my '97 Saturn actually had that diode in the fuse box as a replaceable part that plugged in just like one of the fuses.
The module control has knobs for the blend doors, temp control, and fan speed (has seperate plug in back). It has push button switches for rear defroster, ac compressor, and recirculating air door. The fan works fine, however, I cannot test it to see how much current it is drawing, but I suspect it is actually powered by a relay.
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Originally Posted By: another Todd
The module control has knobs for the blend doors, temp control, and fan speed (has seperate plug in back). It has push button switches for rear defroster, ac compressor, and recirculating air door. The fan works fine, however, I cannot test it to see how much current it is drawing, but I suspect it is actually powered by a relay.
The fan would not use a relay. Older blower motors that had maybe 3-4 distinct speeds used a resistor pack and a toggle switch, but more recent designs use a transistor to control the blower motor speed. If yours does use the resistors and toggle switch, the resistors would most likely not be on the control board but somewhere in the air ducts to keep them cool. At least, that's what GM did for many years.
The module control has knobs for the blend doors, temp control, and fan speed (has seperate plug in back). It has push button switches for rear defroster, ac compressor, and recirculating air door. The fan works fine, however, I cannot test it to see how much current it is drawing, but I suspect it is actually powered by a relay.
The fan would not use a relay. Older blower motors that had maybe 3-4 distinct speeds used a resistor pack and a toggle switch, but more recent designs use a transistor to control the blower motor speed. If yours does use the resistors and toggle switch, the resistors would most likely not be on the control board but somewhere in the air ducts to keep them cool. At least, that's what GM did for many years.
Just a wild hare here, but check the charging system voltage. GM tended to run their voltage pretty high for a number of years, and that combined with a blower motor with stiff/dry bearings or something that puts a little extra load on the switch might just push it past the point of failure. Do you have headlamps and other bulbs fail more often than with other cars?
Common problem. The fix includes adding a jumper or 2. This is all I found on my first search.
http://www.aircondition.com/tech/questio...-and-CK-Pickups
http://www.aircondition.com/tech/questio...-and-CK-Pickups
Chris142 thank you. That describes my problem exactly. When this one quits I will make the repair. One question though...What is actually causing the boards to burn out?
Originally Posted By: Dave Sherman
I would strongly suspect there is something wrong with the blower motor. If this module controls the fan speed, then maybe the fan is running but taking too much current, maybe because of a faulty motor winding. The compressor clutch coil would be my other suspect, and it could even be that the flyback diode on that has blown. I couldn't tell you where that diode is, but I thought it odd that my '97 Saturn actually had that diode in the fuse box as a replaceable part that plugged in just like one of the fuses.
this is all you need to read. (well, until I saw the jumper post--- if the boards are defective then that's that)
motor current is high is my first guess. dirty commutator or sluggish bearings.
good possibility on the compressor, but my bet is the blower.
I would strongly suspect there is something wrong with the blower motor. If this module controls the fan speed, then maybe the fan is running but taking too much current, maybe because of a faulty motor winding. The compressor clutch coil would be my other suspect, and it could even be that the flyback diode on that has blown. I couldn't tell you where that diode is, but I thought it odd that my '97 Saturn actually had that diode in the fuse box as a replaceable part that plugged in just like one of the fuses.
this is all you need to read. (well, until I saw the jumper post--- if the boards are defective then that's that)
motor current is high is my first guess. dirty commutator or sluggish bearings.
good possibility on the compressor, but my bet is the blower.
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Chris came up with a home run for you!
I just have to vent about overly complicated electronics and systems in cars.
There is no need for this here. A simple switch off of a old Maytag washer would last decades.
I just have to vent about overly complicated electronics and systems in cars.
There is no need for this here. A simple switch off of a old Maytag washer would last decades.
Mechtech2, I completely agree. I have considered rewiring the whole thing with off the shelf switches and relays.
The blower motor shouldn't be the problem as it has a seperate switch and power feed.
The AC clutch shouldn't be the problem because a relay actually powers that, and I replaced the relay on the off chance that it was drawing too much juice to trigger it.
I will rewire the control board using Chris's instructions if and when the current one fails.
The blower motor shouldn't be the problem as it has a seperate switch and power feed.
The AC clutch shouldn't be the problem because a relay actually powers that, and I replaced the relay on the off chance that it was drawing too much juice to trigger it.
I will rewire the control board using Chris's instructions if and when the current one fails.
Originally Posted By: mechtech2
I just have to vent about overly complicated electronics and systems in cars.
There is no need for this here. A simple switch off of a old Maytag washer would last decades.
Agreed as well.
Of course this vehicle in question is already 14 years old I can only shudder at the issues later model cars will have in the future. I bet it is going to be darn hard to diagnose those issues not to mention the huge expense of actually repairing those failures.
I just have to vent about overly complicated electronics and systems in cars.
There is no need for this here. A simple switch off of a old Maytag washer would last decades.
Agreed as well.
Of course this vehicle in question is already 14 years old I can only shudder at the issues later model cars will have in the future. I bet it is going to be darn hard to diagnose those issues not to mention the huge expense of actually repairing those failures.
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Anyone can repost the fix for this problem page not found
Wow, rebooting a 9 year old post, well here goes...Rock Auto warranteed the AC Delco part that only lasted 4 months, and the replacement lasted until I sold it some time later, maybe a year or two.
Check this: https://www.silveradosierra.com/how...k-series-trucks-hvac-control-unit-t77522.html
Check this: https://www.silveradosierra.com/how...k-series-trucks-hvac-control-unit-t77522.html
Pictures aren't working for me, so I have no idea if the OE transistors have heat sinks on them. Even with higher current rated transistors, I might want a heat sink on them if there is room for them, depending on the application.
IIRC, on the two of mine that went bad, it was obvious what burned up by looking at it, and it was two different components. And I think there was plenty of room to add heat sinks. Good luck.
If the burnt-out "control unit" was the resistor pack for the fan speed control and the replacement burns out too then you likely need to replace the blower fan. If the fan is going it can draw more current and this will heat up the resistors more causing them to fail rapidly.
Nice necroposting - and welcome to BITOG!
