My heater is not working why?

I can't get the heat to work on my vehicle. The fan blows great, a/c works great, only cool air comes out when heater is on, will not heat up at all. No smells, just clean cool air.

My jimmy did that 2 years ago. Its a 2000 and one shop told me I needed to replace the Heater core. I took it in to a shop that works on the radiator and told me it was clogged up with radiator fluid. They did a huge flush. They said the made a special tool. They seen so many jimmy's with this problem and they fixed it. A huge flush cost me 300 and worth it. A new heater core is almost 1000. Try a deep flush. Maybe a radiator expert shop.

When I turn on the heat it only blows cold air.I have changed the thermostat and flushed the coolant. My brother doesn't think it's the heater core. What else could it be? Some kind of switch or relay?

Took it to a well respected service man just for diagnoses. No heat. He says it is the controls or damper motor in duct work. I swaped out controls with my sons s 10 and it still wont produce heat. Must it be damper motor? If so how easy is it to get to?

Checked hot to cold damper and it works, going to flush system. The repairman felt the hoses going into the heater core and seemed to be hot to both of us, but was not as hot as the top radiator hose. Going to add flush to entire system. Is that the best way to go?

Plugged it was, but I must say it was the cleanest radiator I ever drained and flushed. It fooled me. Thanks jeep

The heater produces heat and the blower works on all speeds. No heat flow is going to the floor when the control is in the floor or blend position for floor and defrost. Instead flow is defaulted to the dash vents only. The defrost only position works. I have visually inspected the control switch and vacuum tubes in the dash. They appear in good shape. Is this a common problem? What is the best (easiest if possible) way to diagnose what is going on?

I have had the radiator replaced, the heater core replaced and the heating system flushed, and when I switch it to the heater, I still get cold air. What else can I do?

Heater problem
2000 GMC Jimmy 6 cyl Four Wheel Drive Automatic

i replaced my t-stat because I was not getting heat in my passenger compartment. Now it only heats intermittently. I t seems as soon as I put a load on, the heat comes, when I idle the heat goes away. Any ideas?

My heater won't change from vent to floor to defrost. So I looked at the vacume lines and they have oil in them. Could it be that the vacuum actuator switch on the transfer case is no good, assuming that where all my vacuem connect to?

My heater is blowing out cold air, I am trying to figure out if its the heating controls or the hot cold flapper (cold hot dock, or vacuum actuator). How do figure out what the problem is between those two. I have already canceled out, coolant, thermostat, water pump, and the heatig core.