Ok so I was driving home last night with the front and rear a/c cranked and the headlights on, I look down at the dash and the volt gauge shows the first big line after 9volts!!!!! so I panic and shut down the a/c and the gauge comes back up. After playing with it for a little bit when I got home I find out that with all the electrical stuff running(full load on the Alternator) I am only charging at 12.5v..turn the blowers off and I get 13.8v........but once you turn on either blower motor.(front or rear) the gauge drops like a rock......so the question is.......do I have 2 bad blower motors? or do I have an electrical problem that I need to find? Any one else have a problem with their blower motor doing the same thing?

 

Might get a test load put on the alt first to rule that out.

 

+1 - I agree.

 

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agree in comcept, but....... "load check the battery", use a DVM to check alternator output.

 

I have had the whole system load tested in and out of the vehicle and everything tests fine......the alternator in the vehicle load tests at 13.2v and the battery tests good too.......... out of the vehicle both test about the same and are within specs.............but if I run both blower motors it is a totally different story.................I am totally lost on this one....................chevrolet wants to change the blower motors and the alternator....all to the tune of about $1000.00 but they cant guarentee that will solve the problem.....I can do the work myself but I dont want to just "throw" parts at it.

 

are your fans making any kind of noise. i had one in my 94 burban almost seize right up had to pull it and lube the $#!% out of it. I notice a small draw before but not as drastic as you mention. it was only the front one that was seizing up tho so... what happens when you run only one and have every other component running in the truck lights radio plug something in the cigarette lighter signal lights etc...

 

The fans are quiet......the draw is minimal with one fan running......

 

Have you tried running both fans by themselves?

 

I think I would get a clip on amp meter and check the current being drawn by each blower. I'm sure you know this but a clip on meter has a clip that goes around the hot wire for any device and it measures the actual current flowing in the wire. With this you can see if both motors are drawing the same current and compare the draw to another vehicle if necessary. If the motors are quiet and not laboring, I kinda doubt they have a problem.
You said the alternator checked out a 13.5v. I believe the normal output should be something like 14.8. I guess their test also included the regulator. They are usually part of the alternator now. When the voltage drops, it means that more current is being drawn than can be supplied. That often points to a weak battery but if all that has been checked, all you can do is see what's pulling the current. Good luck.