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Re: low heater output
There is a water control valve near the firewall where the heater hoses go in to the heater core. Make sure your hoses feel hot when engine is fully warmed up.. one should be hot and the other cooler as it is your return. the water control valve might be faulty not letting water enough get into the core. thanks jerry holler if you need more..
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Bad coolant flow. check for low coolant, also a thermostat could be restricting proper coolant flow. If coolant is full in the radiator than touch your upper radiator hose to see if it is hot. If their is proper coolant level and engine is warmed up to temp and radiator hose is cold replace your thermostat.
Feel your heater hoses. If both are hot, the heater core is circulating coolant, and the thermostat is not a problem. The door controls in the heater case need attention.
If only one heater hose is hot and the other cool, look for a water valve in the heater hoses-may be closed. Or the core has an air blockage or blockage-try to backflush it with a garden hose.
If both heater hoses are cool (on a warmed up engine), then it could be thermostat is stuck open.
How old is the coolant in your car? If you haven't changed the coolant in a couple of years, you may have sediment build-up in the heater core that is restricting full circulation in the core and preventing good heat output. Feel both hoses at the firewall that go to the heater core. Are both equally hot when the engine is warmed up and heater controls on high? If only one is hot, and the other lukewarm, the core is partially plugged. Pull off both hoses there and run a garden hose at low volume backward through the core. If not sure what is backward flow just run the garden hose through both openings and see if you can remove any sediment or blockage. If both hoses are hot, the core may be circulating fine, and the problem may be in the heater case's doors not opening fully- I think that would be the temperature blend door. When heater controls on full heat, the door should be fully open to let blower air pass across and through the heater core to pick up heat and pass on through to vents.
Read all of these instructions before starting this job. First test your heater core for flow by disconnecting both heater core hoses from motor and forcing air from an air compressor into one of them watching for flow from the other. If you have no flow then you may need to backflush your heater core - it is possible you have blockage in it. Your local auto parts store has a backflush kit you can buy that will have a backflush valve ( to be added to your supply heater core hose ) and an additive to put in your coolant system. The kit will not include new coolant so you will need to get that too. Install valve and connect a garden hose.Run motor specified time in the kit. Remove lower hose from your radiator and turn on the water from the hose full blast. Watch the coolant coming out from your radiator to see if any chunky stuff comes out - also watch for the color of the flow. Run water until it comes out clear, then shut off water and disconnect garden hose. Allow system to drain, reconnect radiator hose and cap flush valve. Refill coolant system, turn heat on high and run motor until it is warm. Top off coolant in radiator ( be careful - the pressure may cause coolant to spray out when you remove cap - put a rag over the cap before you remove slowly). If you do not have warm air at this point you may have a bubble in the heater core and may need to block rear wheels then raise the front of the vehicle until the radiator cap is higher than the heater core. Restart vehicle and turn heater on high . Check coolant level in radiator and top off, then cap radiator and shut off motor. Lower vehicle and start again with heater on high. If you still have no heat then your heater core may be plugged. To check, remove both heater hoses from motor and force air from an air compressor into one of the hoses, watching for flow from the other hose - if no flow then core is plugged and needs to be replaced, but if you have flow then you still have an air bubble in the system and need to purge using the above steps until you have heat. Hope this helps and please rate my solution - good luck!!
The valve might seem to be open, but it is actually closed and the actuator has sheared of something. With a cool engine, remove the heater hoses from the engine end and try to either blow through them or use a garden hose to flush them through. Be careful with the garden hose though, it has many times the presssure available than what the cooling system is rated at. If it doesn't flow freely, dont let it build up pressure or you may damage the heater core. Depending on its condition, it may be clogged or the hose has collapsed inside.
try backflushing the heater core,remove heater coolant hoses and flush both ways with a garden hose,do you have a air compressor ,blow water back through heater core both ways,this asuming that all valves are working allowing coolant to flow and all air doors in car are opening,if so this fix has worked many times for me in older cars note works better to hook water hose to hoses or a short peice of hose on heater core,good luck