What's the CHEAPEST fix for my loud ac compressor?

Take it to a qualified repair shop. Quit trying to play auto mechanic .

1989 Mustang speedometer is cable drive so VSS will not affect.
If over 140k miles the speedometer is likely worn out.
My company SpeedometerRepair.com can repair or another speedometer shop.

Is it squeaking noise, Loud rubbing noise? Brake problems? Clanging noise is bad engine problem. Was oil that low that they needed to add it. Have you checked it again since that? Do so immediately, If low, take it back NOW.

Get out your owners manual and locate the power relay for the AC and remove it, this will stop the AC clutch from engaging the compressor, note, AC is used in winter to help remove moisture when defrost is on you may have to roll window down to prevent fogging, also check for blown fuse in manual bet you find one for instrument cluster, good luck,Bret

check AC compressor belt could be slipping.

Just replace the compressor clutch,that is the proper
way to make the repair

Go to a repair shop

We do not have all the info your asking about
We don't do bypassing & cheap,fix it right

forget the boyfriend and take it to an accredited service center for a proper diagnosis and quote
knocks are big ends or mains , and ticks are hydraulic followers
all could be a bad cam but a proper diagnosis will make sure

OOPS ! Now, it sounds like the A/C relay is constantly on. In the power distribution box by the battery, try swapping another relay for the A/C relay (which turns the compressor on), and see if it now stops. If so, buy a new relay. Good luck.

Any leak or damage due to ac compressor failure may cause serious damages. For preventive maintenance, keep track of the part's working conditions to prevent compromising the functionality of other engine components. Good thing premium quality factory equivalents to your stock ac compressor are conveniently available for specific vehicle applications. As the part constantly handles the harsh fluids and tough working conditions, structural weaknesses of conventional ac compressor replacements have been addressed in constantly improving the functionality of the part. When looking for the right compressor replacement, putting you money on quality and durable products is advised.

Try to remove the belt for the ac and see if you still hear the noise, as it sounds like you may have blown the seal or bearing out of the ac compressor , not sure just a guess.