Have the high pressure valve checked.
low on freon compressor kicking in and out
diagram a\c system 1999 grand marquis online
where is the ignition control module located on mercury marquis
To remove the heater core on a 1992 Grand Marquis, first remove the dash board. Then remove the AC box to have access to the heater core.
It would freeze up with the ac running.
In the relay box next to all the other relays.
Most likely the ac belt is loose and needs to be tightened or replaced.
In the center of the dash. It's the unit you select options on. It controls the AC and Heat.
Change the coils .
Vacuum check valves are usually located close to the vacuum source.
http://www.aa1car.com/library/ac_recharging.htm
This is not cost effective. It's quicker and cheaper to replace the compressor.