I agree $1600 USD would buy a car. Also, I don't see how a larger fan is going to hurt unless it's not moving air through the system.
Also, if it's sucking fuel then I'd think the compressor clutch was working... best way to verify is to see it.

Anyway, for any compression driven heat pump to work, you have to have some basic parts working:
A compressor that will compress a gas enough so that it typically liquefies.
A working medium (the gas) - R12, R134a, Ammonia, etc...
Hoses (usually insulated) to convey the working medium.
Two radiators - one to release heat to heatsink and one to absorb from refrigerated space.
Metering valve to develop pressure on high side and slowly release liquid working medium that then evaporates/gassifies.
Heat sink to accept heat. Typically moving air or water.

Methodology:
Compress gas to liquid (liquid wants to let go of heat), run thru radiator (outside) to release heat, meter slowly releases liquid to the low side where it gassifies and wants to absorb heat. Hot gas ready to compress again.

There is a fault when:
the compressor doesn't compress gas to liquid or sufficiently.
there is not enough working medium to compress.
there is too much working medium so that gassification is not possible or efficient.
radiators are not efficient i.e. they do not exchange heat due. Blockage?
the metering valve is clogged or too open to develop pressure.
there is water or unwanted elements in the system.
there is too much or not enough of the proper lubricating oils.
there is a leak in the system.

That's the theory as I understand it...
Your answer is in there somewhere I think.

__________________
Codifex
1981 240D ChinaBlue (Got her running with a donor engine.)
1983 300DTurbo w/sunroof.
1984 300TD manual sunroof. (Electrical Gremlins)