Why isn't my heater not working in 99 chevy tahoe?

probably a blend door issue. switches the system air flow from hot to cold or in between. Check out this guide it will help

https://www.2carpros.com/articles/car-heater-not-working

and

https://www.2carpros.com/articles/replace-blend-door-motor

Please let us know what you find. We are interested to see what it is.

OK heres the deal i have a 99 tahoe and out of no where the heater got stuck on the floor setting and wont switch over. when i turn the knob it doesnt even attmempt to do anything and makes no noise like if it was trying to move so i doubt its stuck or anything.. and other i might add is before it stopped switching over it always did take a while to switch like 5 or 10 seconds at the maximum.. thank you and i appreciate your time and input

In this case, you are looking for a vacuum leak. The vent door actuators are operated by vacuum from the engine. If there is a leak, they won't change. Check under the dash and hood for broken or damaged hoses. With the engine running, you may get lucky and hear a hissing sound from the leak.

Let me know what you find or if you have other quesitons.

Joe

ok so i recently had my upper and lower intake gasket changed. so that would eliminate a vacuum leak under the hood.. i have no idea where to even start to look under the dash.. would you know of a general area to start looking

Start where the control is located.

Heater problem
1996 Chevy Tahoe V8 Four Wheel Drive Automatic 143k miles

i changed the thermostat thinking it was the problem,it wasnt,what do you think the problem is?

With the engine at full operating temp, locate the 2 heater hoses where they go into the firewall and feel them to see if they are both hot to the touch. If they are..........

The temperature is controlled by the use of an air mix door that is operated by an electric motor/actuator. This door can be jammed or the actuator can be inoperative or have stripped plastic gears internally.

Heater problem
1996 Chevy Tahoe V8 Four Wheel Drive Automatic 143k miles

1996 tahoe heater only blows cool air,i tried to feel on the passenger side to see if there was a leakage from heater core,negative,i want to know if it could be the thermostat,and what does the thermostat do

Replace the thermostat its cheap could be stuck open and check the heater core if its clogged-up and the heater control valve

The function of the thermostat is to control the engine temperature-if it shut closed it will cause the engine to overheat and stuck open will cause the heater to be blowing cold air and also the engine will never get to the normal operating temp. and computer will be throwing fuel at all times when not needed-

need help with temp control switch.switch works but will not control the temperature all vacuum lines seem to be good have not found anything wrong with electric

sounds like your actuator isn't working see pic you cold have two or three the temp door actuator will be the one by itself in center of hvac. her eis a tip to install it.
When replacing temperature door actuator it seems necessary to remove the ashtray / powerpoint assy. being careful not to break retainer clips w/o breaking them by squeezing them together on the backside while pulling on the front. This opens it up to easy access to the actuator and screws.The screw on the right side of actuator is easily removed with a 1/4'' socket cap, 5.5 mm socket and a wrench.
make sure to not hook up the electrical until it is installed and centered.

I am having problems with the heater,no heat,changed thermostat,heater control valve and new coolant,still no heat? Someone told me that it could be a blocked heater core? And can the door be replaced on the box that controls where the heat goes to? The door arm is broke inside which controls the air flow? will it hurt the truck to run water straight through the heater core,no valve?

flush the heater core both ways to clean of debris. both hoses should be hot when running.

the door is part of the case and is replaced as an assembly. that may be your issue. try moving the door manually to see if you get heat

Roy

I have a 1995 5.7l Tahoe with 305,000miles that recently developed an irregular heat problem. I have replaced the thermostat, heater control valve and back flushed the system. The coolant level is full, the heater core is not plugged and the heater control valve seems to have adequate vaccum. It seems the heat increases as you accelerate while driving at a constant speed produces little or no heat. I would appreciate any suggestions. Thanks

To me it sounds like the thermastat is stuck open or the collant level is low. With it getting cooler when you drive faster what it is saying is that the fluid is circulating through your engine too fast and the engine not having time to heat it. at higher speeds it flows quicker.