Have 9 yr old a/c system using R22 refrigerant. Evaporator coil needs replacing already and am getting conflicting info regarding need to replace compressor due to R410A requirement. Will mixing the two refrigerants cause the compressor to go more quickly? Should we bite the bullet and get compressor also. If we do both do we also need to replace the heater?

They are totally different fluid bases and will not work if mixed together. Heater does not have to be replaced unless something is wrong but they are a lot cheaper than an AC unit.