96 won't blow hot air

The temperature control switch was checked and seems to be working (I check resistance through the switch). Still blows cold even in the hot position. The A/C Heat fuse is good. I left the truck run about an hour this morning before leaving, still blows cold air. What's next, vacuum, valve, maybe thermostat??

Thanks for replies.

DB

vacuum

Check the coolant overflow tank for rust colored sludge. If exists, see GM service about acid flushing your colling system regarding Technical Sevice Bullitin (99-06-02-012, a copy can be found at http://www.geocities.com/b_gillie/dexcool_problems).

This problem (no hot air) and engine overheating problems could be the result of the Dex-cool antifreeze congealing in your cooling system - as is the case with my 96 Jimmy with the same problem.

Forward and reverse flushing the entire system and repeating with just the heater core should fix your problem temporarily but chances are the problem will resurface next winter. Most will recommend replacing the heater core at about $600 so weight your options carefully.

Turned out to be the heater core. The Dex Cool appeared to have gelled and blocked water flow. A friend of mine and I spent about six hours rolling the dash, flushing the system, and installing a new heater core. Cost was about $80.00. Nothing was extremely difficult and the Haynes manual was helpful in rolling the dash, page 3-8. Make sure you have a 7/32 socket to remove the cover from the core. Don't even try to access the core form under the dash or through the glove box, just roll the dash.

My 97 has been doing the same thing for the last week or so. I'd been checking the overflow and it always had coolant in it, but I took the cap off and sure enough, it was gooped up with brown crud.
I poured 4l of coolant into the rad, and I expect the cap is pooched as well. The temp guage is showing normal temps and I'm getting heat pretty consistently now, but I expect I'll be flushing the entire system shortly.
Thanks for the review of the work!

What's with the whole dexcool thing, it's supposed to last for 250k !

You guys need to replace your radiator caps with the Stant brand from Advance Auto (Stant is the best but any one other than AC Delco will work). The AC Delco brand that originally came on the vehicles are defective, they allow air to get in the system. When air gets in the system it mixes with the Dexcool causing it to foam. When the engine cools the foam turns to sludge and then the sludge clogs the system.

Also, for christ sakes, why did you replace a heater core instead of just flushing it?

Waste of time and money.

Just reverse flush the whole system, replace the coolant, install a new rad cap and drive.