Is it absoultely necessary to replace expansion valve, filter drier, and flush the ac hoses before installing a new ac compressor on a 2001 Mitsubitshi Eclipse?
If the compressor has seized up, yes. In addition you would need to replace the condenser and evaporator if they are parallel-flow type. Compressor failure contaminates the AC system with metal debris and those parts can't be flushed out.
If the old compressor had not seized up but maybe just had leaky valves or a bad clutch you might be able to get away without doing that. However you'll probably find that the warranty on the new compressor requires those parts to be replaced regardless. The drier should be replaced any time the AC system is opened up to atmosphere.
why wouldn't you? Also, I'd replace the condenser (they're like 50 bucks).
If you aren't certain how your compressor failed it could have spewed small metal shavings into your A/C system.
They'll eat up your new compressor in no time.
Buy an O ring kit for it . Replace the drier, expansion valve, and condenser, and then flush the system.
Pull a vacuum on it and then weigh the R134A. Your system takes about 15 ounces. You can use the cans to recharge it, just weigh them before and after so you can be as accurate as possible. (you can buy an ounce scale for under 20 bucks online)
The repair will outlast the car
