Fan operation when NOT on AC [Expired Topic]

2907 Views 15 Replies 3 Participants Last post by ChevyFan, Aug 1, 2006

technojunkie

Discussion Starter · Jul 24, 2006

Here's an interesting one....

So we took our our "new" 99 Suburban on the family's first "road trip" in it down to Oklahoma City over the weekend. Only 120 miles one way, but it was out of town...

Anyway, over the weekend we had a big cold front go thru and dropped our temps from 100+ down to the 80-90s.

I figured, as thirsty as this thing is, let's run with the AC off for a bit in the evenings. We'll just use my old friend - the vent.

Interestingly enough - on 2 occasions now - after turning the AC switch off and backing the temp control out of the "MAX" cold postion to open the vent, the fan will run for a bit, and then cycle off for a bit, and then cycle back on eventually.

Now, we don't have the temperature set climate control system - it's the 3 knob - fan control, cold to hot control, and "where does it hit you" control set. If it had a temperature setting like my buddy's 2002, I would expect the fan to be controlled automatically, but this....

It seems automatic, but I'm not seeing anything about it in the owner's manual (that I just got via Ebay!). Maybe I'm missing it?

I can force it on by cycling the AC on, but that kind of defeats the purpose.

Any ideas?

After GaryL's cogent description of the "magic mirror" operation, I am quite hopeful someone's seen this behaviour before!

Thanks all!

Tim the technojunkie

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GaryL

· #2 · Jul 24, 2006

Here's some possible causes:

http://www.gm-trucks.com/forums/index.php?showtopic=24559&hl=ac+fan

Sounds to me like the switch may be going out.

technojunkie

Discussion Starter · #3 · Jul 24, 2006

Thanks Gary! That info certainly helps!

A little more info - at lunch today it was doing with or without the AC. I couldn't force it to happen, wiggling the switch didn't make any difference. The only setting it worked at was hi blower and max AC. If AC wasn't on max (forcing the fan into REALLY HIGH) the fan might or might not run. If the AC was on max and the fan wasn't on high, the fan might or might not run. Only when both were on high and max did it work every time.

Sounds like either the resistor pack mentioned in the gm-trucks post or possibly the switch. I'm leaning toward resistor pack.

Now if I can just find the darned thing to check it or see what's up!

Thanks,

Tim the technojunkie

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GaryL

· #4 · Jul 24, 2006

technojunkie said:
Now if I can just find the darned thing to check it or see what's up!

Thanks,

Tim the technojunkie

If I remember correctly, I think it is behind the glove box, but I could be wrong.

technojunkie

Discussion Starter · #5 · Jul 27, 2006

Yep - you're right. I picked up the part at the local dealership (~$25) and they printed something off their parts computer showing where it is and it's right behind the glovebox on the left right under the airbag mounts....

I can just get my hand into the crack between the air handler box (where it's mounted) and the airbag mounts, but it's nigh-impossible to get a wrench or socket in there to get ahold of the two bolts to remove it.

It looks for all the world like I'm going to have to pull the passenger airbag to get it out! Any suggestions or alternatives?

Thanks gang,

Tim the technojunkie

ChevyFan

· #6 · Jul 27, 2006

Yikes. I'm always afraid I'm either going to damage it or deploy it when I deal with the airbag.

technojunkie

Discussion Starter · #7 · Jul 27, 2006

Yeah, me too....

To try to avoid pulling the airbag system, I thought that maybe I could get to the two bolts holding it in and work it out of the 3" gap between the airbag bracket and the windbox that the blower motor resistor is mounted to.

So, I spent today dragging the kids around trying to find either a racheting 7mm wrench (I think that's the size - hard to tell where it is) or one of those socket wrenches you can hold in place and twist to operate....

So far I've found a twisting socket wrench, but it's 3/8 and too big to fit.

It's kinda frustrating to fight 2 bolts all day just becuase they're hard to get to!

GaryL

· #8 · Jul 28, 2006

OK, I'm a little confused. I pulled out my glove box and looked back there on mine (it's a 99 as well) and I am trying to figure out which part you are trying to replace. I thought the part was back there, but not sure what it looks like. Which one is it? Could you post a pic of the part or the schematic you got from the parts store? I can see a couple of relays and a small board that is attached to the top of the air box, but all are easily accessible when you remove the glove box. Am I looking in the wrong spot?

technojunkie

Discussion Starter · #9 · Jul 28, 2006

I will see if I can post some pix....

The small board attached to the top of the air box is what I am trying to replace. Two screws, one connector. The problem I'm running into is that just in front and above the module is the air bag module support frame, and I can't get my hands or tools in there to get ahold of the two bolts holding the board in. There's only 3 inches or so of space to get hands and tools thru, although once you're in there you have maybe 5" to play.

I'll try to shoot it and see what you think.

(BTW - I'm not beyond trying to replace the wrong part, but based on the diagram the dealership provided, I think this is it....)

Thanks guys!

Tim the technojunkie

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GaryL

· #10 · Jul 28, 2006

I took a picture of mine, but I can't figure out how to get it on here. It looks like there is plenty of room for a 1/4" ratchet with a 7mm socket to fit in there, unless yours has something there that mine doesn't. I'll continue to try to get the picture up, but it's not looking promising. The gallery says my picture was uploaded, but it doesn't show up anywhere.

Try this:

http://pg.photos.yahoo.com/ph/gary76leta/detail?.dir=4220&.dnm=8bd0scd.jpg&.src=ph

technojunkie

Discussion Starter · #11 · Jul 30, 2006

Yeah, that's kinda what I wound up having to do.... Driving the ratchet from the very end of the handle was a pain, but possible. (I did find a ratchet that has a spinner on the end of the handle - unfortunately it's a 3/8" drive and too big to get in there...)

Well, replacing the blower motor resistor didn't help. The parts guys (and posts via the link earlier) said that it was about 50/50 which one might be it.

Well, looks like after replacing the switch (and the old one did look a little heat stressed inside the connector), it still only runs on high.

I'm going to break it down and see if the connector is hosed - it may have melted inside a bit.

And the saga continues.

Thanks,

Tim

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technojunkie

Discussion Starter · #12 · Jul 30, 2006

Done.

Okay, so in hindsight - here's what happened.

Apparently, the switch began to fail and heat up. One pin (goes to a black wire on the side where there are open spaces) had heated to the point that the female part of the connector fouled MOSTLY. Not all the way - so it worked sometimes.

I took the connector loose from the switch, removed the pin-set plastic piece, removed the female part of the connector for that one pin (yes, I have connector tools to do that, but you could use a really small screwdriver), bent it open just a bit, scrubbed it with a wire brush and scraped the inside where I couldn't brush, reassembled - and 'voila. It works.

The blower motor resistor was a red herring. It's really just a bunch of coiled wires with a thermistor (I think), so there's really not a lot to go wrong there.

Anyway - all is well now!

Thanks for the help Gary!

Tim the technojunkie

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GaryL

· #13 · Jul 31, 2006

Glad you found the culprit. The same thing (melted pigtail end) happened to a friend of mine's 96 pickup. I had forgotten about it until you mentioned it.

ChevyFan

· #14 · Aug 1, 2006

Huh, I've never had something like that melt on me. Glad you found it.

technojunkie

Discussion Starter · #15 · Aug 1, 2006

technojunkie said:
The blower motor resistor was a red herring. It's really just a bunch of coiled wires with a thermistor (I think), so there's really not a lot to go wrong there.

A followup thought regarding this issue -

My brother in law (a Ford tech) mentioned that the blower motor resistor may have been the reason the switch heated up and failed in the first place. If the resistor was not working properly, it could have caused higher current draw thru the switch - overheating it.

So, maybe not a red herring after all...

I gotta say, it's nice to not have to live with no fan or hurricane force blower as the only options!

Thanks guys,

Tim the technojunkie

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ChevyFan

· #16 · Aug 1, 2006

Yeah, I can see that. A failing resistor will do screwy things with the amout of juice going to your motor. If they only put enough solder on it for x amount of current, x+2 melts it down.

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