89 Town Car with no heat

For the past several years my 89 Town Car has had a coolant leak. Since the leak was slow I have been simply topping off when needed. I finally decided
to address the issue and make the repairs. I have replaced all hoses, the water pump, and the thermostat. Leak problem solved. However, it seems that I now have no heat at all. Since I have not run the heater since last winter, I don't know when the problem started.
If I allow the engine to reach operating temperature both supply and return hoses to the heater core are hot. There is a sloshing sound in the passenger compartment when I accelerate, but there is no sign of leaking coolant from the heater core. The car does have climate control, and I have seen posts referencing temperature sensors and blend doors. I am not quite sure where to start first. Any suggestions?
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Number of possible causes. The heater core could be plugged and the internal by pass is doing just that, bypassing. Being this is a 89 the ATC is vacuum controlled. The blend door servo or the control aspirator may be bad. The cable that adjusts the aspirator may be broken. I would measure the temperature of the heater core as a start point.

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