Air conditioning/ heater

After a couple of days of a knocking noise around
the on off switches. Which I was able to stop by
turning the heater / air to off and presses all the
buttons, I did not have cold air anymore. It just blew
90  degrees hot air. Even the vent blows hot air. I
took it to Medike because the sign said free a/c
check up. After 45 minutes they told me they
needed to run a dye in the line to be sure there is no
leak. That was not to be free. Then they added
coolant. After another 45 they told me my car was
ready. They charged me 159.00. The man at the
desk took me to my car and the there was a
problem with the blend door. He started the car and
showed me the heater was on and he turned the
car off. He said this is how I was to make the a/c
work. He pushed the a|c max and started the car
again. Cold air started coming out. He said that will
make it cold. I paid the bill and drove off. A few
days later I tired doing just that. I never ever got
cold again. Five days later I went back to Mineke
and said I felt ripped off. (I'm and old lady) the new
man behind the counter took it back into the shop.
After and 45 minutes he said 'we told you there was
a problem with the blend door they thought. Not
sure what is causing it to stick. It could just be a
spring. But they need to pull the dash. 5 hour job.
They they would be able to know which part was
bad. HELP PLEASE. ANY SUGGESTIONS?