Q: Blowing cold air no heat

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I changed the thermostat it's still blowing cold air what could be the problem
My car has an automatic transmission.

Since the thermostat has been replaced, there are a couple of other things to look at. The heater hoses going through the firewall in the engine compartment to the heater core behind the dash should be checked. They should be as hot as the other hoses to indicate that coolant is flowing through the heater core. If the heater hoses are not hot, then it is possible that: the heater core itself may be clogged, one of the heater hoses may have collapsed internally and is blocking coolant flow, or the heater control valve is not functioning properly. The heater control valve works by vacuum. When HEAT is selected, a vacuum signal is sent to the heater control valve to open and allow coolant to flow into the heater core to provide heat. If the heater control valve diaphragm is broken internally, or the valve is not receiving enough vacuum from the engine due to a broken or detached vacuum hose, it will not open. Also, the heater controls can be at fault if it is not sending the proper signal to the heater control valve to open.

Have a certified technician look into the no heat problem to isolate the correct cause.

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