Heater problems There's very little heat coming out of the bottom. And there is no heat coming out of the defroster. the fan is working properly. I have a 2002 Pontiac Montana the system has been flushed out. I replace the thermostat and the heater core. Could you tell me what could cause this problem Appreciate any help you can give me.

Do you have heat? Does the fan turn on? are you getting air from the defroster vents close to the windshield? If you have heat make sure the defrost control is working. I'd open the outside air vent and turn the blower on high speed. If there is no heat, the heater control valve is not working. Double check the radiator fluid tank, make sure you have enough fluid (antifreeze) Low fluid levels can reduce the hot water flow to the heater coil inside the car. If there
is no air flow through the defroster vents you may have a problem with the fan control, or the fan motor. Good luck.

well the ac compressor will come on if you have it in defrost mode,if heater is blowing cold ,after you just had thermostat replace ,you could possibly have air in system.now if your heater motor is not working which is called the blower motor under dash it could be the resistor that controls it also these rigs have been known for wire harness problems at heater control unit and the blower motor connector.good luck,mike

I'm making some assumptions, here.. I've been told I make too many assumptions... but, I'm assuming that you're talking about the engine cooling fan.. If I'm correct in this assumption, my guess is that you've not taken the vehicle to a good, reputable mechanic or repair shop. There are several reasons that an engine fan would not turn off, and each reason would have to come from a qualified mechanic. For example, there is a sending unit for the air conditioning system that might cause continuous running... or a sending unit in the air conditioning system that could cause the same thing. To complicate that issue, quite likely your air conditioning system purposely kicks on the engine fan any time you run your defroster. Also, your inside heater should function correctly, regardless of the engine fan running continuously. If I'm wrong on that score, then your engine has a thermostat problem "to boot"... which, by itself, could cause poor heating of the inside of the vehicle. NOW, backing up a little, if you so happen to be talking about the fan INSIDE the vehicle that is part of your heating OR air conditioning, we have a little different matter on our hands... First, some vehicles legitimately have a fan running on slow speed at ALL times.. for continuous air circulation purposes (sometimes, you can't actually hear this). Also, I might add that THIS fan running all the time should not be a problem for the heater to work properly.

I assume your heater setting is electric control, if so either your defrost and floor heat switch failed or wire problem. For the air not hot, check the heat control valve on the top of the hose it should be in front of the firewall. I don't know your car is using mechanic valve or electric control valve. Anyway check there first. Good luck.

The cooling fan should come on when the coolant temp reaches around 200 degrees F. regardless of what position the heater switch is in.

The fan comes on when the defrost is on because the defrost automatically turns on the A/C. The A/C dries the incomming air to help clear the windshield.

I’m happy to assist further over the phone at https://www.6ya.com/expert/jeremy_d728a59f986299fa

For this types of problem,i suggest you to check this help links:----Car heater blowing warm, but not hot air?http://schematicsdiagram.blogspot.com/2011/12/car-heater-blowing-warm-but-not-hot-air.html
---------A/C, heater, defroster fan, not working?http://technoanswers.blogspot.in/2012/02/ac-heater-defroster-fan-not-working.html
--------Heater problem?http://technoanswers.blogspot.in/2012/02/heater-problem-on-isuzu-trooper.html
---------Engine Overheats and heater blowing cold?http://howtobyme.blogspot.com/2011/11/engine-overheats-and-heater-blowing.html
-----------Heat blows cold on drivers side and hot on passenger side?http://schematicsdiagram.blogspot.com/2011/12/heat-blows-cold-on-drivers-side-and-hot.html----------------This will help.Thanks.

try blowin out the lines trash in them sounds like it

hi from uk can i offer this advice ? when you start engine let it warm up a little then drive untill temp guage reads warm at least ? then when you put front screen defrost on only select screen and No 2 speed then as temp reaches normal screen will clear fully if you select full speed on heat blower to clear screen at first start it will not work because the coolant from engine passing thro the heater matrix/radiator will be rapidly cooled by fan of heater TRY IT? in years gone by it was common remedy if you were stuck in traffic and temp rose towards hot you could cool system down by putting heater on full heat and the fan on max this cooled the engines coolant as it passed thro the heater ?hope you understand how heater/fan should work for optimum efficiency my wife has owned 2 of these accents and never had heat/demist problems it is surprising how many people consider the demist/heater systems are poor on many cars not just hyundai hope this helps best wishes

If it is blowing hot air out of the defroster and not out of the heater vents then the door that directs the heat from the defroster isn't working properly it is blocking the heat from going to the heater vents. Also check the cold air door. It sounds like it isn't closing all the way to shut off the cold air and not letting the hot air pass.

a kink in the hose will cause poor water flow so it will be slow to heat and may cause the heat not to be as hot, as for the defrost, check the operation of all diverter doors, should be vacuum controlled, you may have a vacuum leak under dash or missing hose