Fan sometimes only works on High.

[imidazol97]

Originally Posted by happydog500

My fan works good most of the time. Sometimes it only works on High.
It still happens after I replaced the Control Unit on the dash and, the Blower Motor.
If it starts acting up, it always works on High, but not the other 3 settings.
Can't tell for sure, but I think it could be coming out very little, like lower then the lowest setting, on the first 3.
Chris.

I keep reading your description and since _none_ of the three speeds works, I wonder if your trouble is a relay in the relay center. I tried reading my service manual for 1998 and it has two relays. The electrical diagram is confusing to me as to how the two relays differ.

But I believe your relay that connects for the low three speeds and feeds power to the selector switch might be burned, and only making contact part of the time. Usually one of the series of resistors burning out would leave 1 or 2 of the three speeds working, but not always if the last resistor of the series burned.

But for the relay would be the 3rd or 4th from the left (passenger) side in the bottom row of relays. If you look at the relay part number--in large blue letters on mine--most of them are the same part. If the part number is the same as 2nd from the passenger side, then you can switch the one with the 2nd from the passenger side which is the horn relay temporarily to see if it is the problem.

It may be the two relays for blower control are the same part number and can be switched with each other. If my thinking is right, switching them with a bad contact would give you the lower speeds but NO high blower speed. A cheap test!!!

Only switch relays that are the same part number.

The electrical diagram for this is strange and I may be misinterpreting it. But I'd look at the two relays.

[jd-autotech]

if you pull that blower motor resistor out and look at it. its got a small electronic pc board and it will be burnt looking that resistor applies resistence to all blower motor speeds except for .... you guessed it high speed. i am sure thats your trouble 2-3 screws and a harness and thats all there is to it.

[happydog500]

Originally Posted by jd-autotech

if you pull that blower motor resistor out and look at it. its got a small electronic pc board and it will be burnt looking that resistor applies resistence to all blower motor speeds except for .... you guessed it high speed. i am sure thats your trouble 2-3 screws and a harness and thats all there is to it.

Thank you for your help.

How do I get the fuse panel off? The whole thing has to come off to get to the resistor. I can't even get to the bolt on the right side.


fyi. From what I can tell, I believe the relays controls 1 and 4, 2-3. The resistor is for 1-3. So, if I only have 4, it's the resistor.

Now, if this doesn't get me, after a day or two of only having 4, all day today, they all worked.

I read in the GM Service Manual that the resistor usually works or it doesn't.

I need to get the Max Fuse Panel off just to look at it.

[imidazol97]

Originally Posted by happydog500

fyi. From what I can tell, I believe the relays controls 1 and 4, 2-3. The resistor is for 1-3. So, if I only have 4, it's the resistor. .

But there's a relay also in that series electrically. And the other thing mentioned in the Helm factory service manual is checking the connections at the resistor board.

The onlypicture I found of the resistors is this. They are actual physical resistor wires as I had thought. Only one of those coils is in series with the entire set of 3 circuits for the 3 speeds. If it were broken, you'd have no speeds; BUT it would stay broken. It would NOT go on and off more than a few times--that would be if the ends of a break were touching again and made contact, like a light bulb that sometimes works again, but eventually the ends are burned back beyond contact. Any of the other two resistors breaking would have left you with 1 or 2 speeds working. You didn't state that in your description. Therefore, I concluded either last resistor broken or a contact at connection or a relay contact has burned and makes contact part of the time.

If it doesn't work, tapping on the relay might effect a remake of the circuit through a burned contact--easy test.

Here's a resistor pack for manual blower control.

Originally Posted by happydog500

Now, if this doesn't get me, after a day or two of only having 4, all day today, they all worked.

I read in the GM Service Manual that the resistor usually works or it doesn't.
.

That a "resistor usually works or doesn't work" is what makes me think it is not the actual resistor pack. In cars with the auto temp control, the resistor pack is replaced with an electronic blower control module which can do funny things and work in strange speeds. But yours is not a blower control module.

[HotZ28]

Originally Posted by happydog500

How do I get the fuse panel off? The whole thing has to come off to get to the resistor. I can't even get to the bolt on the right side.

Have you change the relay yet?? You will need a 1/4 in drive 10 mm deep-well socket with a magnet insert and either a flex extension, or universal joint to remove the two panel nuts. Once the nuts are removed, you will be able to pull the fuse/relay panel forward, far enough to access the resistor. Be careful, do not drop your nuts!

[jd-autotech]

i have seen plenty of burnt resistors work and not work.

[happydog500]

OK, figured it out. We looked at the Resistor, it was melted.

My friend and I wondered; If it says in the book to look for melted wires, this means it's a problem. How come it gets so hot?

Second thing he kept wondering, how come it doesn't blow a fuse before the plug melts?

Here is the pictures we took;





We couldn't get the part (internet said they had it, but when we went to the store, they didn't have it.
The plug is almost as much as the Resistor. I will go by the wrecking yard to see if I can get a plug. I may as well get the risistor when I'm there.

Thank you for the help.

If it says in the book to look for melted wires, this means it's a problem. How come it gets so hot?

How come it doesn't blow a fuse before the plug melts?

Chris.

[HotZ28]

Very common failure on the resistor/relay manual system, seen it many times before, hence the mention of "melted wires" in the manual. IIRC, the fan blower is on a 50 amp fuse, which leaves the terminal plug & wiring at risk. The resistor is just that, it creates resistance in the circuit to lower the voltage to the motor. Resistors "resist" the flow of electrical current. The higher the value of resistance (measured in ohms) the lower the current will be. This particular terminal was underrated for the load, hence the overheating & eventual burnout.

[happydog500]

Since I put it back together, I want to know if anyone of you know if all 4 wires are hot all the time? Or is certain ones hot depending on what setting it's on?

Until I get another one, I want to keep current off the end wire. Anybody know what setting the end is?

This could help me not burn up my car.

When I get the new plug, do I just cut the wires, then connect the new plug onto the wires?


Still kind of wondering why 3 of the conectors are fine, with one totally melted.

Thank you,

Chris.

[HotZ28]

The orange wire is used for HIGH speed, light blue for MEDIUM, and tan/yellow for low, & BLACK for ground. What color wire is going to the burned terminal?

[happydog500]

The burnt wire was black and brown.

Just kidding. I believe it was the light blue.

When the UIM goes out, people don't get the stock from GM. They get an aftermarket.

Since its' a common problem, any place to get a better plug? Not the resistor, but the plug on the end of the wires.

I still wonder why all 3 are perfect, with one wire totally fried. I would think it would be at least more equal.

When the wire burns, is it usually the same one? What makes that one wire take all the heat, with the others not at all?

Thank you,

Chris.

[HotZ28]

Light blue, being the medium speed (more commonly used) pulls more amperage than low speeds, because the fan is running @ a higher speed with elevated amp draw with the resistor in line. The high speed runs with a full 12-v. It's also possible that your fan is drawing more amps than it should due to age. You should check that when you put the new connector & resistor in. RockAuto has an ACDelco plug, & most replacements come with beefed-up wires & terminal.

[happydog500]

Is the ACDelco at Rockauto with beefed up wires and terminal?

The "arctic Blast" starts tomorrow. Supposed to get down to zero. The wind is very cold. I was going to go to the wrecking yard to see if I could get one in the morning (before it starts cooling). If I order from Rockauto, I have to drive my car around with the melted plug for a week. It is scary for me to do that.

Although, I may not be able to get one from the wrecking yard. I wasn't looking for this part, but I think most of the GM's there where the auto kind. Plus, I think if they have ONE, it will be melted like mine.

Do you know if the ACDelco is beefed up?

Thank you for replying,

Chris.

[HotZ28]

The last ACDelco (identical harness) I bought from the dealer several years ago, was the "beefed-up" version. I could not speak for what RockAuto has to offer on this particular part, they may be made in China now!

[happydog500]

Thank you.

I went to the wrecking yard today. It was cold. Went through a few cars, they all had two plugs (mine only one). None had the control on the dash (to see if manual), so we had to pull the fuse block on each one. Hitting knuckles in the cold wasn't fun.

While we where leaving, I went up to an older car (90?) that didn't look like mine. I saw it had the same plug, so I got the plug ($2). At least I think I got the right plug.

The Resistor plate part was shaped different, so I didn't' get a resistor.

I am going to order the Resistor now. I don't understand why, but I'm ordering from Jerry's, the most expensive place in town for this part. $16.99, $17.99, Jerrys at $21.99.

There is a little white lock, that holds the tab from comming out. I broke it on my original, and on the one I got. The main tab on the Resistor is still there, just not the little white part. I think I'll be alright without it.

One friend told me to put the wires together, then shrink rap it. I thought of getting the butt connectors and crimping.

Is there a best way to connect the wires?

P.S. The part I got at the wrecking yard, looks like it's brand new, no melting, color change, burnt or anything. My worry about the ones in the wrecking yard being melted like mine was unfounded. Just my negativity.

Update It was cold, looking at it in the wrecking yard, it looked "brand new." After looking at it with a magnifying glass, I can see a little corotion in two of the connectors. It's been used, but the plastic is good. Here is a photo.

Chris.