I am a HO in Lancaster, PA with the need for some of the sage advice of this forum. My current system is a 4 ton Carrier HP (38YH048-3) and a Carrier AH (40QBS049-3). The back-up heat is from an Opus water storage system (to reduce electicity costs), and the air distribution is in two zones, controlled by an Enertrol system. The house is approximately 3,800 sf.

The system was installed new when we built the house in 1990, and has provided a very satisfactory level of temperature and humidity control.

Our one problem with carrier was with a "defective" inside coil that sprung a leak about 39 months after installation (36 month warranty), and we had a lot of trouble getting Carrier to acknowledge that the construction of the coil was at fault. I swore then that I would not buy another Carrier product. (I've mellowed a bit on that point.)

Our service technicial (original installer) tells me that the accumulator is leaking, and that with the age of the system it would not be wise to repair the leaking accumulator. So, we are now in the process of looking at alternatives for replacement of both the inside and outside units of this split system.

Several points have surfaced that seem clear to me:
1. We can change over to a system that uses 410A rather than R22 coolant.
2. We can increase the SEER rating of our system significantly from about 7-8 to 13-16.
3. Adding a variable speed fan in the air handler will improve efficiency in cooling and in dehumidification.

Several other points are less clear:
1. Will a multiple speed or multiple stage compressor add to the efficiency of the unit, when used with the two-zone Enertrol air distribution system?
2. Is there any value at all in a UV germicidal lamp in the air handler?
3. Is a simple replacement of the outside unit with a similar size and efficiency Carrier unit a realistic alternative, or am I just asking for more trouble?

Sorry about the length of this post, but I'm trying to give all the information that might be needed to provide guidance on this decision. Thanks for any help you can give.