I have a 2000 Chevy S10 Pickup. It is blowing cold air from the heater. I was wondeing if anybody may know why it is blowing cold air.

The heater core may have deposits preventing the heated antifreeze from circulating. If you don't use distilled (de-mineralized) water with your antifreeze, you run the risk of getting deposit buildup. You may have to remove/replace the heater core. Another possibility is a bad heater control valve.

Have you checked, or ever replaced the thermostat?
Also make sure the heater "door" is working; it may have a vacuum leak not letting it close from outside air-to-heat air.
Just my humble opinion...

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Mine 99 s10 had the problem with no heat and then found the dexacool anti freeze is bad for cars and trucks with cast iron block and aluminum head. The antifreeze gels up and clogs the heater core I took the heater lines off andblew air into the heater lines and all kind of look like jello coming out drained all the anti freeze out of it put in green anti freeze in it and I have no more problems and my truck has 165,000 miles on it GM knows about this but there not going to tell you because they will have to replace a lot of car and truck anti freeze hope this helps. You can also email me at [email protected]

I just fixed mine!. I took the 2 hoses off that went in the fire wall. I took my air compressor and blew air in the fire wall inlet to blow any junk that might be in it. I put the hoses back on and (wow)... big time heat. 3 years with no heater and that's all I had to do? At least it was a free repair.

Just fixed mine. Turned out to be a clog in the heater core. Noticed hoses were hot up to the fire wall but cold at the fire wall. Sure sign coolant is not making it through. Removed both hoses (Used screw driver, ground a point on it and bent 90 degree angle to work between hose and heater core connector - don't poke through hose!) then took a new hose attached it and blew into the heater core. Nothing - it was blocked. Drove forced air through with a paper towel rapped around nose of the air gun to stop air from escaping - but enough to let over pressure pass. Core fluid broke loose. Reattached hoses. We have heat again!