1997 vt 3.8 commodore heater not heating valve hot one hose into firewall hose blower working.

Some early cars have what is referred to as a hot water valve under the hood . It is hooked in one of the heater hoses , the supply side . The other hose is the return side , once the hot coolant goes through the heater core it goes back to the engine to get heated up again. This hot water valve is operated by engine vacuum. If you look at the fire wall or bulkhead , you should see two hoses going into the inside of the vehicle. those are the heater hoses. look for the valve on one of them. If you vehicle doesn't have one of this valves , you possibly have a mode or blend door problem . Does you car have Electronic Automatic Temperature Control or manual A/C-heater system ? The heater blower does work , all speeds ?

check small vacuum hose on rear of square inlet manifold top that goes throught firewall ( bulkhead ) is not cracked or has come off
it goes into cab near heater hoses. this is the vacuum supply hose
if you have no vacuum the heater controls default to go to windscreen. also check the black & white plastic little round one way valve for leaks & operation
also check vacuum hose that goes onto heater tap that is in right inner gaurd under brake master cylinder area for leaks and that its on the heater tap valve
if they are all ok check inside do you hear any hissing noises behind dash controls or down at front centre console area?

have 2002 altima,blower works no heat at idle and very little heat when accelerating.I changed carbon cabin filter,made sure little gear under dash to temp knob wasnt broken,flushed and bled system.Nothing worked so checked hoses to heater core and found inlet hose was hot,outlet hose was not.So investigated this problem and came to conclusion heater core was clogged.An easy way to check is to get car to normal running temp. put on heater and blowers at full.Go under dash on passenger side where counsel meets firewall,this is where heater core core inlet and outlet aluminum tubbing go through firewall,you will be able to feel both tubes one closest to you is outlet, so if this one is not hot and and other is your heater core is clogged.I detached both inlet and outlet hoses to heater core from water control valve.Then I blasted water with waterhose and nozzle set at jet,first through outlet hose to blow gunk out,then through inlet hose until water runs clear.Reatach hoses fill and bled system.heater works great nice and hot!

Check to see if the heater core hoses going into the firewall are hot when the engine radiator hoses are hot. If one heater core hose is hot and other is cool, then the heater core is blocked/plugged. If they are both cold then the hoses are blocked. Trace them both back to the engine and make sure there is no on/off valve on the intake to turn on. Some of those valves are vacuum operated or electrical. Just depends. For a quick fix. You can remove that valve and install a screw in fitting to the intake manifold that has a barb on the end to slip a hose over. But the heat will always be on hot.

Open the hood and with the heater running(be careful PLEASE), feel the lines going to the heater core(2 hoses running to the firewall, to the blower motor). Is one of them hot? If both are cool, your relay valve to allow coolant to the heater core is stuck. It will have to be replaced. Is the blower fan running( that's the fan in front of the firewall)? If the valve opens but no fan running, you will not get hardly any heat. If all that is working, You have a problem with the vent control valve(that will open the hose duct to allow heat to go through the vents). It works off of vacuum. A hose may have broken (they are made of rubber), or it may be just stuck. Check these first, before looking at the heater core. I hope this helps you

Start with the engine hot and the temperature selector in the cabin set to max heat and the blower on. Raise the hood and locate the hoses going into the heater core (through the firewall). Check if both hoses are hot to the touch. If not, locate the control valve in one of the heater hoses and feel if it is hot on one side of the valve.

Have an assistant move the temperature selector inside the cabin. Watch the valve in the heater hose to see if it moves. If not, look for the problem with the mechanism. If it does, replace the thermostat.

There are one or more of 3 following things may contribute to the problem. Need to check out: 1- The flap valve directing air flow through either the heater core when we need the heat or the evaporator when we need the AC gets stuck. 2- The valve control the amount of hot coolant flowing through the heater core to control temperature get stuck not opened. 3- The heater core gets clogged up. It may get recovered by flushing.

Hello

I recently had a simular problem...try to follow the heater hoses that come from the engine and go into the firewall to the heater core... one of the 2 hoses connects to a plastic valve right before the firewall. This valve shuts off the flow of hot coolant into the heater core when heat is not needed.. Look carefully at this plastic valve, there is a wire pull cable with a small loop at the end that connects to a lever on the valve. Have a helper work the heat controls and make sure the cable pulls on the lever at the firewall valve...I've seen some cables disconnected. Hope this helps with your diagnosis.

There are 2 hoses going through the firewall from the engine, these are the coolant hoses to the heater core, one is 3/4" and one 5/8", the control valve should be in the larger line (3/4") which is the inlet, make sure that the valve has vacuum (heater on low), also check and see if both hoses get hot with the heater blower on low, if they do get hot your problem is not the heater control valve but the air temp control blend door actuator.

Under the hood on the pass. side firewall are two heater hose lines. Start the car and let it get at normal operating temp. One of the hoses is the "in" to the heater core, if you touch it it should be hot. The other hose is the "out" of the heater core, this hose should be warm and not really hot like the "in" hose. If the hose going in is hot and the other cold, then your heater core is clogged. There is a valve connected inline with one of the heater hoses, this is the heater control vavle.
If the valve does not open, you will not have any heat either.