There is more than one thing that could cause this. It could be as simple as a bad connection or worst case it could be a blower motor starting to go bad. Next time it isn't working, locate the motor and tap on it. If it starts working, that is a good sign the motor is going bad.
On the firewall to the right (when facing the firewall) of the blower motor.
I tested mine by putting wires with alligator clips on the blower's terminals and touched the other ends to my battery.
( No ) The blower motor is in the engine compartment . It is near the firewall towards the passenger side of the engine compartment in a 1992 Lincoln Town Car
The problem is either the blower motor resistor or the blower speed selector switch.
I assume that you can see the blower motor from the engine compartment It would be near the firewall ( the metal wall that divides the passenger compartment from the engine compartment ) on the right side ( towards the passenger side ) of the engine
on fire wall engine compartment
Try looking behind your glove compartment / corresponding location on engine compartment firewall.
If the reservoir is blocking the way, then it will have to be removed.
where is the oil sending located on a 1993 Lincoln town car? where would i find a discriptive picture of the of a 1993 Lincoln town car
blower motor resistor thermal limiter is blown. Replace the blower motor resistor.
Blower Motor Resistor is located under the hood on the fire wall behind the right valve cover and the heater hose. It's about the size of a deck of playing cards.
On the engine side of the firewall located approximately behind the position of the HVAC control module in the dash