What can cause no heat problem in a 2000 Mercury Sable - Ford Taurus?

Answer 1

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The blend door on a 2000 Mercury Sable is not operated by vacuum therefore, verify the coolant is at the proper level, verify the thermostat is operating properly, check the inlet and outlet nose lines to the heater core.

Those hose lines may be too hot to touch for any length of time so use caution. The outlet temperature should be almost the same as the inlet temp. A large difference may indicate a blocked heater core. Flushing the system may help, replacement of the heater core may be necessary.

If the coolant level is low there will not be enough liquid in the system to adequately circulate through the heater core. Fill the coolant to the proper level.

A malfunctioning thermostat would prevent coolant from circulating throughout the entire cooling system. A higher than normal heat gauge reading can indicate the need to replace the thermostat. There is a small motor that controls the temperature blend door that regulates the amount of air passing through the heater core. The actuator motor is a common problem.

The blend door itself can also bind-up and or break - that's not good as it, just like the heater core, is buried down deep under the dash - considered to be a major repair, a.k.a. $$$