My 2004 chevy trailblazer starts to stall, and sometimes die's completely when I turn on the defroster or the a/c. What are ther possible causes, and fixes?

SOURCE: loss of power

ignition coil/switch

SOURCE: I have a 2004 chevy trailblazer when I turn the

I had the same problem and was told the air intake valve was not opening and needed to be cleaned, to allow the air flow.

SOURCE: when i turn on my heat my 2004 trailblazer stalls

if this happens while the defrost of ac is turned on, it could be a seized ac compressor which will cause the serpentine belt to squeal and drag making the engine sometimes stall. if it happens with the ac off and the selector on say the floor, or dash vents, the issue could be a bad alternator and battery. this is confirmed when the blower motor engages and the lights dim and then the truck goes dead.

SOURCE: 04 trailblazer AC leaks

Rather than pay the dealer $350+ to fix this, I found the "L" shaped drain hose behind and interior to the front passenger tire (I let the car idle with the AC on and waited for a drip. On my back on groud I reached in and found the drain line and it came off i my hand and about 4 oz of water and some decayed matter floowed out. I reaced back in and found the hole to which the L line was attached. It was a rubber fitting on the end of a metal pipe. The fitting came off easily and then about 8 oz of water flowed out (carpet had been soaked for two days). I reattached the L drain line and noticed that inside the fitting was about 1/4 tsp of "mulch" - decayed leaves, pollen, etc. Reattacted the fitting and water now flows freely out the drain. And yes, its a very high humidity area - Houston, TX. And if you live anywhere near here you know about the intense yearly dispersion of Pine tree pollen. I thisnk that accelerates the blockage. Happen about every 2 years. (Third time for me. First two I let the dealer over charge me for this effort. BE SAFE WORKING UNDER YOUR CAR!

SOURCE: 2004 chevy trailblazer-Reduce engine power

You need to get the fault codes read to determine where the problem is that set the SES light. Autozone will scan your car at no charge. At some point you will need to get a mechanic involved to further diagnose the codes.