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Automotive blower motor relay

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ke5frf

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Hi all, looking for advice on an "annoyance" issue with my vehicle's AC controls.

A while back, the blower motor in my 2001 Chevrolet Blazer (S10) siezed up, of course blowing a fuse.

Replacing the blasted thing was a pain, but I managed to do it no problem. Of course, having been in a shorted condition the wires and connections got hot throughout the circuit.

This vehicle has 205,000 miles on the engine and transmission and still runs well, so it is paying dividends for me to keep it going, but I don't like investing too much money in it. When the engine or transmission goes, so will the Blazer.

Anyhow, not long after replacing the blower the relay failed. At first I thought it might be the resistor network under the hood, and simply replaced that. The failure occured one blower speed at a time, starting with high. But replacing the resistors did no good. So I got a new relay.

Bingo, problem fixed, for a while. After a few weeks the high speed went out again, then not long after that the other speeds went. The relay was a cheap aftermarket, but for convenience sake I bought another one and went to replace it. I found when taking a closer look that the female terminals in the connecting cable were burnt, probably from overheating when the original motor failed and I hadn't noticed.

I'm kind of lazy and figured I'd just try scraping the contacts, squeezing them with pliars for a snugger connection, and go. So I did, and replaced the relay again.

Well, it took longer, but eventually that relay quit working too.

So now I'm at the point where I'm not going to waste money on more relays and want a cheap, easy solution. So I have an idea.

I happened to save the last relay, and today I broke into it to have a look. After checking it with an ohm meter, it doesn't appear damaged...well, I take that back, I suspect the coil. It is made of very thin wire.

It ohmed out at 90 Ohms. It has a parallel resistor (blue, grey,brown=680 ohms) I'm not sure what the coil should read, but typically I would expect near shorted. So perhaps the coil is what keeps going bad.

The contacts seem clean and pass continuity when manually pushed closed or in the NC state.

I'm thinking there is a high resistance somewhere at a connection point that is keeping this relay from working properly.

As I said, this is an old vehicle, not worth putting money into, so here is my idea. Instead of buying a new wiring harness for the relay, I'm thinking I'll just clip the common wire and the wire for the contact that energizes the fan when the closure occurs. I'm assuming that would NOT be the NC contact, but the other one. Basically bypassing the relay and having the fan run full speed all the time. Actually, the fan only runs when the AC switch or heater is on anyway, so I'm only giving up the variability.

I'm thinking to solder or crimp contact point#87 and #30 on the wiring harness and just remove the relay from the circuit (to prevent problems if someone moved the speed switch).

I don't have a wiring diagram and don't know what might "bite me" if I did such a thing. Anyone have experience with this?
 

Menticol

Active Member
Well, maybe the wiring seems good at the time of your test, but remember the vibrations and movement of the road, maybe a non insulated section of the wire (thanks to the overheatig/fire) is touching the chassis (That's why random time pass before failure re-appears).

Maybe is a ghetto solution, but what about running a wire from the fusebox to the fan?
 
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ke5frf

New Member
Well, maybe the wiring seems good at the time of your test, but remember the vibrations and movement of the road, maybe a non insulated section of the wire (thanks to the overheatig/fire) is touching the chassis (That's why random time pass before failure re-appears).

Maybe is a ghetto solution, but what about running a wire from the fusebox to the fan?


The car has 205,000 miles on it. Ghetto is OK :p

Perhaps you are correct about vibration, but I don't think this is the case, because a new relay ALWAYS fixes the problem temporarily. Sometimes even reseating the old relay does the trick, which I've done on a few occasions.

I really think it is a poor connection being made and to fix it would require replacing the wiring harness, which at this point would be more money to spend on a comfort related problem rather than a motor,ignition,cooling system, or transmission problem which are the only things I might consider spending money on at this point. The only functional issue that arises from a faulty fan is defrosting windows on a cold day.

I could bypass everything and supply power straight from the battery with a manual switch I suppose, but that would too closely resemble work (hehe), and time is the same as money, right?

I'm definately going to bypass the relay unless someone offers me a reason not to that I don't forsee.

But thanks for the suggestion!
 
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ke5frf

New Member
OK, well I went ahead and performed an experiment with the old relay that I had taken apart. It is obviously the coil that keeps failing on these cheapo relays. Or simply a bad connection SOMEWHERE that is preventing voltage to the coil.

The variable speed has four states, 1,2,3, and 4(hi). Pushing the relay contact closed is only good for hi speed...1,2, and 3 are the NC position. All speeds are either intermittent or failed when the problem occurs. The relay is very flimsy and the NC position that governs speeds 1,2, and 3 is tenuous, very light contact being made.

Pushing the contact closed kicks on hi speed, this occurs with the ignition key on or off, so I'm going to sacrifice the hi setting and be satisfied with 1,2, and 3.

I can internally jumper 87a to 30, and I can remove one of the male pins for the coil to avoid conflicting switch closures (87a-30 jumpered while 87-30 pulled in) Or perhaps it would be just as easy to cut pin 87 out of the circuit instead of messing with the coil.

I'll have all speeds but hi speed, which isn't neccessary anyway.

Hopefully someone else who experiences this problem in a chevrolet will learn from my experiment.
 
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