Dying Blower Motor/Electrical System Can't Keep Up with AC

[fledermaus]

Lurked for awhile but this is my first post, so if this is covered somewhere I haven't found yet, feel free to point me in the right direction.

I have a 94 C1500 Sierra with the 5.7l. I don't drive it much (it's got 133k miles on it -- I've put 6k miles on it over the past 2 years). We took it out about 2 weeks ago to scout some off-road trails for a race. Ambient temp was about 90*. We were driving slow (lots of stops and starts) with the AC on, blower on high. I noticed the gauges were getting down around 12 volts. Eventually it stalled while I was driving on one of the paved roads (about 45mph), so I killed the AC/blower and restarted the truck. We ran for a while with no AC and it seemed to charge back up. This only seems to be a problem when we're not driving at a sustained speed.

AC was recharged last year and is cold. Alternator replaced in 2009. At idle with nothing on, reading 13.9v at the battery; when AC kicks on and fan on high, it's around 13.6v. (Gauge voltmeter reads ~ 0.5 v lower than what's at the batt).

Some culprits -- I'm wondering where the biggest problem is or if the rest are just red herrings.

* Blower motor squeals on Med (the 2nd position). It has no Low. I got it this way from the PO and replaced the resistor. It immediately blew the low position. Wondering if (in its death) it is drawing a lot of amperage and just slowly draining when we're at lower RPMs (like under 2000).
* Idler pulley bounces when the AC comes on, otherwise it stays stable. Appears to move approx 1/2" under load (no real squeal -- wondering if the spring actuator is tired -- or is this normal?) If this is more than normal, perhaps the alternator is slipping under load as well?
* Red Top Optima was purchased in 7/2007. I've had mixed results with Optimas, but I think most of that had to do with their use (no battery tender; used on vehicles that drew a lot and sat for long periods of time).

Where should I start? I was going to replace the blower motor and yet another resistor. I am wary of blower motor work as the daily drivers I've done in the past seem to have had the blower motor hung on the assembly line, then they built the car around it. Looking at the Haynes for the truck, this seems like a super simple job. Is it really as easy as it looks?

How about that idler pulley?

And as far as parts suppliers go -- I had my first interaction with LMC a few months ago. They did a great job, but I was a little surprised at the aftermarket parts. I'm used to going aftermarket with my Swedish cars because genuine parts are so darn expensive, but given the lower costs of GM parts, should I just go Delco?

Thanks.

[scotts62]

Thats about the weirdest ghost i have heard about

Im not sure where to tell you to start actually..

Anyone else have any thoughts??

[ChevLoRay]

from the Heart of Arkansas!

If the blower motor is "going bad", I'd suspect that the bearings were the culprit. With that said, a bad bearing is going to cause an additional load (friction) that shouldn't exist if they were good bearings. If there is wear, the armature could be in closer proximity to the field windings and also create drag. Switches may not be able to handle the additional current load created by a "dragging" motor. So, I'd throw a new motor into the equation and see what happens. I've not had to change mine, but an eyeball on it should tell you what you need to know. On my '69, you have to pull a hood hinge. So, I understand your statement. My Tundra was the easiest I've ever seen....inside the cab and right at your right foot on the passenger side.

The battery connections consist of stacked cables on the positive post, and that is a primary spot for corrosion to build up between the cables as well as the bolt that holds them onto the battery. Another possibility is the issue of corrosion within the battery cables. It'll build up resistance and can affect anything that relies on that voltage AND the current necessary to operate it.

If there is an issue with the current flow, it could affect the load on the alternator. The voltage that you read isn't reflective of the current load. An ampmeter would be a good thing to have to give you an idea of what's happening. It may be that the increased load on the alternator is why the idler is acting like you say. The purpose of it is to maintain the proper tension on the serpentine belt. If the belt is stretched, the idler will stay busy. If the load varies, it will "monitor and adjust" for that....as it is its' job.

[speedygonzales]

You may have a combination of things happening. We know your blower motor is shot if it's destroying the resistor and has no low speed. That's the easy part of the equation.

Now does the alternator have the socks to keep up with demand? Don't know that yet.

Let's explain a common motor/alternator failure a little bit just for information purposes.

If you've ever had a starter that gave you problems, especially when hot. Then chances are you tried to crank it over and it just spun real slow. Often times they were ok when cold but drive it for a while and park it then come out a few minutes later and ssssllllloooooowwww cranking.

What's happening here is the windings are shorting together. Normally the varnish that coats the wires won't allow the windings to contact the adjacent windings. But over time, this coating wears and the windings begin to short together. This can happen with an alternator as well. With the motor, as more and more windings short together, the motor has less and less resistance and therefore pulls more and more current. Eventually it gets to a tipping point that the battery can not give it enough to crank it.

In the case of an alternator, when charging you should generally read at or over 14 volts across the battery while the engine is running. As you place more and more loads on the alternator, the voltage at the battery may decrease. Remember that a 12 volt battery actually produces 12.6 volts. It is from the 6 cells, each one produces 2.1 volts.

If you see 12.6 volts or less at a battery in a running vehicle, that means the charging system is NOT charging. The voltage must be over 13 volts at the battery just to maintain.

Never trust a gauge in the dash for accuracy. Always check with a meter.

As far as the tensioner goes. There is a common failure among alternators that is generally the bearing. Many times, it due to a sticky tensioner that does not travel smooth. It goes back and sticks for a split second and then releases and then boom a bunch of tension on the belt. This kind of jerky loading and unloading can make a good bearing bad in short order.

You mentioned the alternator slipping. Possibly, but usually you hear it slipping. Particularly if it's under load like trudging up a hill and so on.

The point here is I recommend anytime an alternator is replaced. The belt and the tensioner should be too. Keep an eye on the idler pulley too. Remember the bearing in it can lock up at any time.

So change your blower motor and then check load to the battery with all the accy's you can turn on at one time. If under full load, you dip below 13 volts, you have an issue. Then it would be time to address it and find out what that is.

By the way. If you try to charge an Optima, or AGM battery. It has very specific rules for charging that a normal wet battery does not. If those rules are not adhered to, damage will result. Optima's website has the rules.

[fledermaus]

Hi:

Thanks for the very detailed responses. I ordered a new blower and the resistor from LMC last week before anybody wrote back. The bearings are definitely shot in it -- they squeal on and off. I used the truck for a run to the dump this weekend and noticed the motor lost speed when it started squealing again, so I'm going with the idea that the blower is drawing too much amperage right now. I should get the parts in the middle of this week. Looking at everything, I seriously think it will take about an hour to swap it out, compared to what I'm used to doing: http://www.cleanflametrap.com/ (the guy's home page is dedicated to a blower swap in the daily driver I have).

RE the other stuff:

* serp belt has about 5k miles on it.
* main batt cables are good and clean. I always use dielectric grease and sealer on them.
* still getting 13.9 v across the poles on the batt with no accessories on. My other cars use Bosch or Nippon/Denso alts. The Bosch never seem to put out more than about 13.9 fresh out of the box. I've uses aftermarket external regulators and set them to ~14.2 v or so at idle with good results. Since I don't have the tow package and I've got a 1/2 ton, I believe I have the smaller alternator -- is there a way to up the output easily?
* Optimas have both saved me and been the bane of my existence. My yellow tops have been in offroad race cars that ran additional Hella H1 driving lights (4 of them). Amazing what they've suffered in terms of heat, discharge, and abuse (especially when we've lost an alt) in the heat of a race, but when it's not critical, they seem to never work properly. Red tops I've had better luck with.

I'll check back in with results after I change the motor next weekend. Then I need some help with diagnosing the front end. Thanks again! Cheers.

[fledermaus]

Looks to be resolved. This was the easiest blower motor I've ever done. It took me an hour and 5 minutes (including changing out the resistor), but 15 of that was fiddling around trying to get the bracket for the ECU (or whatever electronic control unit that is) back in place. Bad angle, big hands. The batt is now getting 14.35v at idle, with the AC fan on high, it's at 14.25v (dash gauge needle between 13 and 14v).

Some tips if you have to do replace a blower motor (Haynes isn't very helpful):

* It's all 7mm hex head screws. A 7mm ratcheting box wrench would be handy for some screws. (I don't know if they make them -- the smallest I have is an 8mm). I did it mostly with 1/4" socket and hand drivers with both shallow and deep sockets and a short flexi (spring) extension. There were a couple of places where it was just awkward to get the 1/4 socket driver in there with the short socket and I could only do about 1/16th of a turn at a time.
* I had to transfer the ground spade to the new motor assembly
* Get the assembly with the fan on it. Some assemblies that require the transfer of the fan blades require shaft modification.
* There was a plastic cover on my fan housing -- insulation for noise, mostly. This was the worst part to get off.

If you have to do this, here is the basic gist on a 94:

* Disconnect your batt (give it a few minutes since you'll be removing the ECU).
* Remove the glove box liner
* Remove the right kick panel near the floor (3 grabber slots in the wall) -- this may not be necessary, but I did it.
* Disconnect the ECU and slip the two clips off the left side of it. The ECU will slip to the left and come out easily.
* You may have to remove the 4 screws holding the bottom portion of the dash in place -- in my case, I probably would have been fine with just removing the 1 for the courtesy lamp.
* Remove the ECU bracket. There are 4 screws that hold it in place -- 2 in the top somewhat hidden in recessed holes that go into the top of the fan housing, two on the side of the housing. The top 2 must come out all the way (these are a pain to put back in). The 2 in the side just need to be loosened -- the tabs on the bracket are notched, so just lift it up and out.
* Disconnect the power (purple on mine) and ground (black) wires.
* Peel the fan insulation boot off the top of the housing and back down.
* Undo the rubber hose going to the fan motor -- swing it out of the way.
* Undo the screws in the fan housing (I think there were 7, but I'm going from memory). Clock the fan motor slightly so the flat edge is flush with the dash, tilt down to the floor slightly and it should slip right out, unobstructed.

At this point, I needed to transfer the grounding spade to my replacement housing. I wire brushed some corrosion off of it and bench tested it.

* Install is reverse of removal, as they say.
* Screw the motor back in, reconnect the hose.
* Slip the insulator back on.
* Reconnect your wires. I'm paranoid so at this point, I reconnected the ECU and then turned on the ign and tried the A/C. Things were good. Then I disconnected the batt and removed the ECU again.
* Reinstall the ECU bracket (you'll find yourself swearing).
* Snap the ECU back in and reconnect it. This is easy -- the 2 connectors were color coded on mine -- one was red, one was blue. Might be a bit of a problem if you're color blind.
* Reinstall the kick panel.

At this point, I also replaced my blower resistor, which is at the top of the motor. To do that:

* Unscrew the two screws on each side of the relay stack.
* Disconnect the right-most relay, then swing the relays to the left.
* Disconnect the two sets of spade connectors (there is a 2-spade and a 3-spade connector, so you won't mix them up; the 3-spade was toward the front of the truck on mine).
* Undo the 2 7mm screws. This is a little awkward with big hands.
* Install is reverse of removal.

Everything's hooked up, so I reconnected the batt and tested again, going through each speed of the fan. It was fine.

* Put your glovebox liner back in.
* Enjoy a quiet, healthy A/C blower with all speeds!

I'll keep an eye on the alt, but I think I'm good at this point. Cheers.