1992 Volvo 240: Heater delivers hot air even with control set to cool. I suspect it is the heater valve, not the connecting cable (as there is still tension when you slide the dash control). How much of the dash has to be taken apart to troubleshoot/repair? Where to begin? Is this a job for a semi-mechanical person? Is this an expensive repair if I take it into the shop?
mark in rochester
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First, make sure your coolant level is full. After spending some time looking around you probably have a shut off valve in the engine compartment. See if you can locate 2 black(sometimes red) heater hoses, about 1 1/4 inches in diameter, coming from the firewall on the passenger side. The heater control valve is located inline with the hoses. It turns on and off the flow of hot water through the heater core which radiates heat in your passenger compartment. Check with your parts house to verify this by looking up the control valve.
It blows cold air with the mode selector in what position. If it is on defrost and you have the temp adjusted to full heat than the a/c will be on to dry the air before it hits the windshield, this helps to remove the fog from the windows. If there is no heat coming out the vents than you need to check to make sure the blend door is working. You should hear a distinctly different sound out the vents when you turn the heat from full cold to full hot. Also check to see if the heater core is plugged. With the engine warm you should be able to feel little difference in the temp of the two hoses that go to the heater core. If one is hot and one is cool than there is a flow issue. Either the water control valve is bad, it is not being opened by the HVAC control head, the is a vacuum leak to the control valve or the heater core is plugged. Your vehicle may or may not have a valve that controls the flow of hot water to the heater core.
First check your fluid in your radiator if its low your heater will not work. Check all your heater hoses and make sure they are not kinked.
Your heater core may be plugged That will stop the heat flowing as well. If it's the heater core it will have to come out and replaced most likely. Not sure if there is a heater valve on that car.
The heater operates from the hot water from the engine cooling system flowing through the heater radiator which is inside the air ducts under the dash. I suspect that the control wire/cable that goes from the heater control lever has broken or become disconnected from the heater tap that controls the volume of hot water through the heater radiator. Some times there is also a flap in the air ducts that is operated by the heater lever tha varies the amount of air that is heated. The tap may be in the engine bay or tucked in behind the air ducting.
Check the heater control valve. It is usually behind the engine up next to the firewall. Have someone inside the car move the heater control to heat. A lever on the heater control valve should move when this is done.
This valve allows hot coolant to enter the heater core inside the car. If this hot coolant doesn't arrive, you have no heat.
The heater in your car depends upon a flow of hot coolant going through the heater core in order to get hot air into the car. If the heater core is partially plugged, it will restrict the flow. If you have a head gasket that is putting exhaust into the cooling system, it will eventually get into the heater core. When this happens there is no coolant in the heater core to make the air warm. If the water pump vanes have corroded away the result will be very poor coolant circulation causing the heater to not blow hot air. If your car is equipped with a heater control valve that is not functioning properly, the coolant flow will be restricted. One or a combination of these factors is likely the culprit in your case.
if the car is not overheating, the thermostat is working fine.... replace or flush the heater core multiple times to try and eliminate sediment build-up.