my heater stopped functioning altogether after I took it to a mechanic to have the oil and air filter changed. .

The heater was completely functional up until the mechanic serviced the car. When I
turn on the heater the fan blows cold air but the temperature never rises and the
interior of the car gets unbearably cold.  I took the car back to the mechanic after the
heater in my daughter's car stopped working altogether after the same mechanic
worked on her car.  We took both cars back to the mechanic but he refused to look at
my car after I asked why both cars had the exact same problem and insisted the
mechanic inspect the cars for any loose connectors or wiring that might have been
dislodged in the course of being serviced.  I believe the repair shop is scamming
single women by forcing them to return for additional service, that is, to reconnect the
wiring to the heater as was the case for my daughter's car.  The mechanic refused to
inspect my Lexus after I suggested that the problem was more than just coincidental.