99 Suburban - blower will not work on high

I have a 99 suburban and the blower works on all speeds but high. I have replaced the fan speed switch and the blower relay. I measured 12v at the relay from the 50A fuse but when i short it to the fan wire nothing happens and the voltage goes to 0 but the fuse doesn't blow so this is not a short. I'm guessing I have a connection probelm in the wiring under the 50A fuse wiring harness? I can feel the relay energize when I switch to HI so everything acts like its working. Its been in the 100s everyday and I really need the high fan to work.

 

Have you checked the blower resistor to see if it's open on one of the legs? It's a four wire connector and it's probably going to be on passenger side of the fire wall. It's roughly hexagon shaped and held on by two nuts/screws.

Christopher

 

probably a open winding in the blower motor itself just replace the silly thing

 

The relay which is working, bypasses the resistors and allows 12V from the 50A fuse to go directly to the fan for high speed. The fan works on all the resistor speeds. The same wire from the fan then switches to the 50A 12V for high speed. My problem is this voltage drops to 0 when switched to high and the fuse is not blown and still reads 12v. This has me stumped and we are projected to be over 100 for the next 7 days. O joy.

 

How are you testing that wire? If you are using a two-prong test meter with one probe on the hot-source wire from the fuse, and then using the other probe to the fan wire, you are 'in series' and will get 0 volts. [This is akin to with a house light switch, to try to see if you have current at the switch, leading to the light bulb, by putting a probe on each of the switch terminals. Doesn't work. You get 0 volts...even when there is no problem with the switch or light, and you DO have proper voltage...because the test is 'in series', instead of going from your hot source directly to ground, rather than going through a resistor (a light bulb in this case...a motor in YOUR case), on it's way to ground.] Meaning, the test is incorrect and won't tell you anything about the motor other than that current is entering the motor and going somewhere. But obviously it is not going into spinning the motor. It could be shorting to some other winding or something. If it's not the switch, it must be SOMEthing about the motor that isn't right.

 

My checks are to ground using a voltmeter. As I noted the 50A source voltage is at the relay socket and I can jumper it to the fan wire and nothing happens. I can jumper the resistor voltage to the same fan wire and the fan blows fine. The relay is working but that doens't matter becasue as I noted I am shorting the high voltage source to the fan and it drops the voltage to 0vdc and doens't blow the fuse. My next test is to run a jumper directly from the batt + to the fan. My circuit drawings show the 12V high power coming from the 50A fuse but its possible my drawings are incorrect since these cover about 10 years of suburbans. The wire colors match the drawings though.

 

Any GM experienced electrical techs out there? No one seems to understand this problem.

 

Some GM's have double wound blower motors. 1 set of windings to handle the lower speeds, and 1 set (usually heavier I've been told) to handle the high speed setting. I'd be looking towards a new blower motor as suggested..

 

Problem solved this morning – found a plastic connector between the 50A fuse source and the relay located just above the fan. Wiggling it caused the fan to work on high but within several minutes the connector was too hot to touch. Took apart and the contacts were melted into the plastic housing – why in the world do you use plastic on 50a circuits? Cut the connector off and butt spliced the wires together and now works great and the wire doesn’t get hot. Doesn’t GM realize people in hot climates use the high setting the most? I would call this a design flaw. My Haynes book did not show this connector – time to buy the service manual.

 

I am having the same problem with my blower on my 2004. Is this connector located on the outside firewall or inside the cabin and where?
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