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Thread: AC/ Heater

  1. #1

    Default AC/ Heater

    I bought this 04 Silverado Z71 Crew Cab. 3 months ago. Everything was good i was running around and it started to rain and the window started to fog up. So i turned heater on defrost. Now i cant get it off defrost. I can run both heater and defrost but only in defrost mode. I changged out the control unit . But nothing! I also bought a delta series flowmaster catback exhaust. I started hearing the engine reving up and down when i was in overdrive. The tach aint moving with the sound.It almost sounds like i have a stick in it and I'm in too high of gear for that rpm. Did some Googling found there was problems with both tranny and tachs in these trucks. So i took it to a local trans guy. He took it for a run and then smelled and felted the tranny fluid . He told me that since the truck came with 265 and i have 285's on it. either i do 1 of 2 things have gm reset pc for new tire size or go back to stock. If anyone can help me with my 2 lil problems. It would save my brains a lil stress. Thank you

  2. #2
    Master Mechanic
    Join Date
    Apr 2009
    Owens Cross Roads, Alabama


    ive ahd a smilar problem with my defrost..its done it a few times..its happened a few took a few tries to get it to switch back but it finally does every time..not sure what causes it yet
    2004 Silverado 4x4
    1986 K5 Blazer
    8" Superlift w/39.5 super swampers
    1992 GMC Jimmy "Blue Bomber"
    4.3L Vortec

  3. #3
    Sr. Mechanic sc99z71's Avatar
    Join Date
    Feb 2007
    Moncks Corner, SC


    I had the same tranny problem that you have except I didn't know what it was until it got worse and would go in and out of Overdrive. With it sometimes going out of OD and not going back in, and if I drove like that for a while I would get a really hard 1-2 shift. What is happening is your Tourque Converter is not fully locking up in OD and the 4L60E is designed to slip to a certain degree. They want to make it smooth instead of shift like a truck. I also have 285 tires. My solution was the TransGo shift kit SK4L60E put in by the local trusted tranny shop who said this is a common problem for these trannys. My buddy at work is having the same issue and is about to take it to the shop.
    99 Silverado 1500 Z71
    5.3L 4L60E Tranny
    TransGo Shift Kit
    2.5" Rough Country
    Suspension Lift
    33" BF Good A/T
    Cherry Bomb Turbo
    Cobra CB w/
    Dual Fiberglass Antennas

    01 Kawasaki KLR650

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