T_P_S

Okay so randomly coming home one night and I smell burning electronics/plastic. Took the HVAC control head unit out and observed, and the switch that is connected to the sliding bar selector for the different modes (Max, Norm Vent Defrost etc) was smoking and burning a small hole through the top of it as if it was shorting out. It only did this in the off position, every other position works perfectly. The fan motor works well, all four speed are available. When "off" I could hear a small whining noise sometimes when I shut the car off that I do not believe I have heard before. Took the HVAC selector out and dissembled/cleaned and reinstalled but same result.

I unhooked the fan speed selector switch. The HVAC selector switch no longer smoked/got hot and I could cycle the compressor on and off and through all the different modes but of course with no fan.

So, how should I tackle this problem? Again the switch only heats up and smokes in the "off" mode. I am going through my factory manual now but if anyone has directly dealt with this issue or has any advice I am would really appreciate it. It really appears to be something with the fan that is causing that selector to heat up.

Thanks!

T_P_S

Okay so, small update. It appears that even with the HVAC selector switch turned to "off" the blower will run and can be selected to run in different speeds, but it seems a little intermittent.

T_P_S

Okay well I am getting proper battery voltage through the selector switch connector, it appears the problem may be isolated to the selector switch itself which really sucks because they are hard to find.

It's definitely shorting inside the selector switch, but I am concerned that there is a reason behind it. Or could it just be that after years of use it's just worn out somehow and it's making connections it shouldn't? I am hoping I don't get a new one and it gets fried but I am not really sure what else to look for.

Any advice for things to check specifically?

T_P_S

Okay my problem seems to be the same as what happened here, however this was never confirmed as fixing the issue.

https://www.thirdgen.org/forums/elec...ke-out-ac.html

The HVAC selector is burning in the exact same spot as pictured here. Perhaps it is the blower switch after all?

Something in the blower circuitry must be creating a lot of resistance or something as inside the selector switch it is "jumping" a gap and shorting out and that is causing the melting. I am just not sure exactly how the HVAC selector switch and the fan/blower circuitry is connected.

Still could use some help!

sofakingdom

iTrader: (1)

The problem isn't that switch; kinda like, the reason a fuse blows, isn't because the fuse is defective. Something else somewhere else is the cause.

Nothing is "creating a resistance" or "jumping a gap". That much is for sure. More likely, wires are crossed somewhere, or something (such as an aftermarket thing of some sort) is wired wrong.

Disconnect the blower motor relay and see if that fixes it.

T_P_S

There is zero aftermarket equipment installed, everything is still factory and it's a low mileage garage kept vehicle. I've had this car for almost a decade and this just randomly started.

It does seem to be something in the blower circuitry. If I disconnect the blower speed switch it does not heat up and start smoking. Can that be causing it or does it have to be be the blower relay or the motor itself? The blower itself works fine and the speed selector switch also appears to work fine.

I'll take the relay off and test the resistance I guess, how else can I pinpoint that as the issue and not the blower switch itself?

T_P_S

Reporting back and I am still no closer to an answer.

Checked the resistance of the three blower resistors, they were fine at 08. ohms, 0.3 ohms and 0.2 in the series. They appear to be getting the proper voltage from the switch but when different modes are selected the wires that "should" have 0 volts have .1-.3 volts in them not sure if that's normal.

Blower motor high speed relay (I'm guessing that's what you mean Sofakingdom?) checks out, 0 ohms through F but it did have only 0.01-0.02 ohms through E and ground but manual just says "less than 3 ohms" is acceptable. I don't believe this has anything to do with the problem though.

All the switches are getting correct battery voltage to them through their connectors.

So I tried a few things. Sofakingdom, when I unhooked the high speed relay it does the same thing. When I unhook the connector from the blower resistors but leave the blower switch hooked up it does not do it. Obviously unhooking the blower switch it doesn't do it either.

I did notice something new though: When the HVAC selector switch is "off" it smokes a little. However, I tried turning the blower switch up to the higher settings (M1 and M2) with it "off", and as I got to the higher settings the spot on the HVAC selector switch got hotter and hotter (got brighter and brighter orange). Moving the HVAC selector to any setting other than "off" immediately stops this and everything works correctly. Even with the HVAC selector "off" it seems the blower switch is allowing more and more current to pass through the HVAC switch.

I really have no idea what else to look for, other than assuming the blower switch is bad. I traced the wires and nothing is melted or worn through as far as I can tell, non of the connectors have melted or anything either.

So that's all I've got, the HVAC switch is burning up only when "off" and turning the blower switch to higher speeds makes it burn hotter, still open for ideas while I get new switches.

Thanks

NINÅ

T_P_S

Thanks for the reply. I have disassembled the unit. I can't see anything that might cause this but I am not even sure where to look...the wires and connectors look fine.

I took the HVAV slider/selector switch apart and it looks really simple, I am not sure how that would fail but I can see where it's heating up at the junction in the off position.

You're talking about shorts or insulation failure in the wire harness and the connectors for the switches right?

I got a new fan switch and a new HVAC selector switch coming so I'll see if that fixes the issue. Still worried it'll do the same thing even with new ones but I cannot seem to find the issue unless it's something very nondescript in the wiring.

NINÅ

T_P_S

Okay installed new switches and been cruising around for several hours over the past week, all seems good!

Doesn't mean you shouldn't check everything else first before installing new switches. They are getting hard to find so you don't want to burn them up!

Thanks all!

Scorpner

iTrader: (4)

I just saw this today. Glad you got it fixed. If you're dealing with something like this in the future, you can ohm to ground (with power disconnected) to locate the short instead of plugging things back in to watch for smoke or heat up. Sometimes shorts "go away" because a wire was moved while unplugging etc., however when that happens the wires can eventually vibrate, or work their way back again. By metering you can more often preserve the symptom until you can locate and confirm the short.