Ive had a 1999 4.3L Blazer LT 4WD for a few years now and have had problems with the heater specifically. The AC runs perfectly fine yet the heater and defrosters don't seem to work at all. Sometimes when I"m driving, especially on the freeway, air can be felt coming through the vents even if the heater and AC are both off. I don't know if this is related at all but I thought it was worth mentioning. I've read into this a little bit and have heard it could be the blower motor or the resistor but I don't know how to tell if those components are the problem or if it's something else entirely. With COVID going on I'm just trying to button up loose ends on my vehicle while I can.

Thanks

 

The blower does not come on in heat mode or it blows air but is not hot?

AC blows plenty of air?


George

 

The air is coming out but it isn't hot. It seems to be whatever the temperature outside is which is generally cold air when I am trying to use the heater. The AC appears to work fine. Not the greatest AC but it keeps things cooler during the summertime.

 

The air is coming out but it isn't hot. It seems to be whatever the temperature outside is which is generally cold air when I am trying to use the heater. The AC appears to work fine. Not the greatest AC but it keeps things cooler during the summertime.

Sorry, new to this forum and still figuring out how it works.

 

Your good, I just need to understand your problem completely.

After the truck warms up feel the two heater core hose going into the firewall. Are they hot, warm or cold. Careful these can be very hot.


George

 

I'll have to check that and get back to you. I very much appreciate the help

 

Sorry this took so long. The hoses were warm when i felt them after the vehicle had been running for a few minutes. I just drove to the gas station about 5 minutes from my house.

 

If both hoses get hot and are the same temperature then you have hot water flowing through the heater core. If those hoses only get warm then you may have a coolant flow issue. Do you ever hear gurgling in the dash? This would indicate a coolant system that is not completely purged of air. If one side is cooler than the other then there is a heater core obstruction.

If you have good blower air flow and good coolant movement then it might be the blend door which is not moving to allow air flow over the heater core. I have never been into this part of the system but Christine knows this well and maybe she will chime in.


George