Hi. I've got a 2017 Hyundai Elantra and I've been having a problem with my heater. While I am driving it blows out super hot air but is cold at idle. If I stop at a stoplight, stop sign, or park the car, the air will start blowing out cold. I took it to the dealership and they had it for 2 weeks. They said they replaced the thermostat and that it had something to do with the computer program. They said they had to reset it 5 times but that it was working fine now. But it isn't. It keeps happening. I'm going to have to bring it back but I'd like to have them look at some other things that could be causing it. Any suggestions?

 

Hi Nancy,
I have a little problem with the answer you were given. I'm not too sure engine revolutions are affecting heater output by way of the vehicle computer.
There are a few possibilities that might cause poor heat at low engine RPM..
Among those could be ,
Low coolant level,
possible trapped air in the cooling system (Did anyone do any engine work that allowed some air to get into the cooling system)
Questionable water pump performance (Sometimes a water pump impeller gets loose on the pump shaft )
Restricted coolant hose(s) limiting amount of hot coolant going to heater assy (There may be a problem with the module that controls heating /cooling)

What needs to be verified is: are the hoses that go to the heater core both hot when the engine is at operating temp. Run 10-15 minutes. If they are , then we would look for how the movable doors on the duct work are working. They are controlled by the HVAC module.

 

Some times the heater core is clogged
When the engine is running, coolant flows and heat gets exchanged. Works good.
Then while at idle or stopped at a light, the flow is restricted so little to no flow. No heat.

Heater core flush could help??