Heater doesn't work

If you are trying to locate some kind of water valve that routes the hot water to or away from the heater core, no such animal exists anymore. Hot water is always routed thru the heater core whether or not you are using the heater. The blend box under the dashboard has flappers that move to route air either thru the heater core, the A/C evaporator, or thru a bypass that routes around both. The blend box allows you to set temperature by adjusting the flappers. It also controls where the air goes; defroster vents, floor vents, or dash vents. If you are not getting heat, the problem is most likely that the blend box flapper is not operating correctly. This could be due to a sticky linkage, a bad vacuum motor, or a faulty control head. You could also have a clogged heater core, or a thermostat that is stuck open all the time. If you are getting heat and don't want it, the blend box flapper is also the most likely cause.

If it is not leaking, you probably don't need to change it. There are flapper doors which direct where air goes in the system. The flapper used to direct air through the heater core is not working. This can be caused by a vacuum leak anywhere in the engine or heater/A/C unit, a bad leaking control head, or most likely a bad flapper door actuator, hidden deep under the dash. See shop manual.

The usual cause is a malfunctioning electric actuator on the air mix flapper valve in the HVAC box.

Pull the heater control panel out of the dash and inspect the blower speed control switch, look for signs of a burnt connector to the switch, it will be discolored looking, if this is the case replace the switch and install a repair connector

CHECK SEE IF HEATER BLOWER MOTOR WORKING, REMOVE HEATER BLOWER MOTOR HOT WIRE HEATER BLOWER MOTOR SEE IF BLOWER MOTOR WORKING BLOWER MOTOR FAULTY OR YOU HAVE FAULTY WIRING AT BLOWER MOTOR AND RESISTOR.

flapper door inside duct work not opening and closing properly. check my tips section for heat diagrams

Feel the 2 tubes at the firewall for the heater core. If they are not getting hot, the heater core needs to be flushed out or replaced. I had this problem with a 1990 Cadilac Deville, it was just a plugged up heater core.

Remember to install sealant after flushing out the system to prevent leaks.

check water pump working and no leaks..might be vacuum line not opening the flapper door or heater core, or heater control valve

the problem maybe heater core stopped-up. need to see if coolant is flowing thru heater core.and check to see if heater hoses are getting hot near heater core . if take off heater hoses to core with water hose run water thru one side of the hoses to see if water flows thru the other hose.

The sliding switch on the console is stuck in the cold position and the knob is pulled off. Use pliers to jiggle the switch as best you can. Feel under the center console and you probably will find the cable that is hooked up to the flapper. You'll know because when you jiggle the cold/heater switch at the upper console, the cable will move slightly. At the hookup of the cable to the flapper down under the console (passenger side) try to work the flapper loose to the open (or close) position. At the same time work the sliding switch (with pliers). The flapper will come loose and function properly. Try not to knock of the AC button like I did in the process. It flew off some where under the passenger seat. I'll find it sometime before summer. Ha.