What year is my Duotherm Air conditioner

some of the wires from duotherm unit not used may be for external sensors not on the coleman unit. have to look at wiring diagrams to know

Do you have the digital thermostat? You can tell the thermostat you have no furnace. You should be able to disconnect power at the furnace, but the 12v power for the circuit board is provided by the furnace circuit on some systems so make sure you disconnect the wire going to the furnace and leave the wire feeding the circuit board.

the return is open to rv through filter. the supply is ducted and you can't access it.

thermostat or communication cable to relay module.

If it's the pencil type, it just pokes into the fins (carefully)
If you look real close with flashlight you should be able to see where it poked in before, usually a couple of inches up from bottom. If it's the little round disc, it snaps in down in bottom corner, there should be a small hole for it in the frame.

When you say loud, do you mean as in airflow noise, or vibration like noise? I take it this is a ducted system as well. Does it have quik cool option on ceiling assy.?

Make sure the coils and fans are clean.
Unless there has been a leak in the lines this will solve your problem.

check condenser fan if running. it will make compressor comes on and off if broken

If this unit has a spark ignition you may just need to clean the flame sensor. It is a metal rod protruding in the path of the flame.

check the thermostat