1990 Nissan 300ZX air conditioning

I took my car to the dealer because the air conditioner started to blow warm air. They first thought it was a seal or a line, but later said the
compressor was leaking and it needs a whole new
air condition at a cost of $2600.00. I ok'd the repair
and now they have installed the air conditioner but
it won't blow over 70 degrees and now the
heater is not blowing either. They were trying to charge me to figure out what they screwed up.
Now they say the problem is the vent door won't
open and the heater worked fine, and the air blew
when I took it in there. I think they have hooked it
up wrong. Do you have any suggestions? They now
want me to meet with them and they have had the
car almost 3 weeks!