Have a 96 Jimmy and am able to get some heat but cannot control how much. I generally have heat at the feet and sometimes on defrost but not as warm. Any common problems that any one knows about? I have checked for checked for heat on the coolant lines running into the firewall and both lines are warm. I have also checked the rheostat for temp selection and it functions as well. Any information would be appreciated.

Does the engine reach the operating temperature of 190-210F?
Check your radiator coolant level with the motor cold.

had the same problem on my 2000 Bravada ... disconnect the heater hoses at the engine and flush out the heater coil in both directions ... it fixed my problem...

I ended up cutting my input hose off (the one coming out of the engine on the passengers side - not the one that goes to the front of the engine).. that one was just simply a pain and would not come off, but when I put the box cutter to it, it didn't give me any trouble at all .. haha.. a new one cost me $16.90 at Advanced Auto...

when I was flushing the heater coil, I used an empty washer fluid jug to put one hose in and used one of those little brass garden hose sprayers to stick inside the hoses to flush....

Good luck...

The engine is getting up to temp, approx 160 F. both lines in return to th care are hot as well......???

I agree with Chris your Operating temp should be more like 190 - 210 .... I suppose you could have a Thermostat stuck Open .. they are cheap and easy to replace.... Make sure you have enough Coolant in the system first, if it's full, you may wanna change the thermostat...??... just a thought...

As a side note... before I flushed my core, one hose was pretty damn hot, the other was "fairly warm"...

Flushing the heater core works good...just be sure to disconnect BOTH hoses and flush one at a time with the other open and not ever-ever restricted. Direct the stream into the open end of the hose but don't try to seal the end with a rag or hand until you're sure the core will take the flow WITHOUT BUILDING PRESSURE or heater core damage can result and a heater core change has been reported as difficult on that year Blazer.

160 is too cold. It should be 195+.