1996 K3500 AC problem

I got a problem with my AC.
First off, I only have high and low speeds for my fan. I all ready put in a new switch and it worked in all the speeds for a couple months and
then right back to only high and low. The guy at the dealers parts department told me that there is some sort of regulator or something on my firewall that is the problem here. Although he never heard of this problem allowing low speed. And definately not working just by installing a new switch.
What do you think?
My main question here is that when my AC is on high, most of the time it blows out great. But sometimes, after the truck has been run for a while, it doesn't really come out at all. The blower is still on high, you can hear that, but no air coming out, anywhere. Is there some sort of trick here? Is my truck just f..king with me?
I am planning a trip from Michigan to Texas around Labor Day, for 5 days, and I need that AC blowing great, consistantly cold.
What do you think about this?
-Tim
(Sometimes I wish I never would of bought this truck.)
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change the RESISTER
its behind the glove box on top of the HVAC enclosure. You may have to pull the dash to reach it

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It's on the inside firewall, what a pain in the ass.
I will do that, hopefully, tomorrow.
Thanks. -Tim
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Shut it off for 10-15 minutes and see if it blows again. I'm betting the evaporator iced over, most likely from a slightly low refrigerant charge. Regards, JR
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I did notice that my accumulator iced over. Is that the same thing as the evaporator?
-Tim
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The accumulator is the oversized beer can back next to the housing that contains the evaporator. If the accumulator is icing up then be assured the evaporator is too. For some reason when the refrigerant charge on a newer A/C system gets just a little low, it will blow extra cold air and then less and less air as the evaporator fins develop a coating of ice. Eventually the coating of ice will block the air flowing thru the evaporator. I believe the liquid refrigerant flashes to vapor a bit too soon due to the low charge. Any A/C techs out there please correct me if I'm wrong.
This happened on my '97 Yukon and was remedied by having an A/C tech top off the refrigerant, and it still occurs with a window unit I have in my home. Regards, JR
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Ok, with the help of Bruce (by e-mail) and others (JR, SnoMan and I'm RIght), I found that I had a vacuum problem. I got a new vacuum hose and installed it and been driving the truck for 2 days and haven't had the problem again. I have even had it running for 2 hours or more at a time.
I still need to change that resistor.
Thank you everybody.
-Tim
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