I have a bryant Model 655ANX042000AAAG
Overall the unit is in great shape no leaks, but has just experienced a compressor burn out. Currently installed is a Copeland 42K recip compressor. The base of the unit is stamped and drilled and tapped to take a scroll compressor also. I would like to use this unit to cool and heat a smaller space therefore, would like to install a 30K scroll compressor. I know that the efficiency will be increased if this can be accomplished. By downsizing the compressor, shouldn't I also reduce the size of the piston orifices? (indoor evap coils and outdoor evap coils). Any help or suggestions would be greatly appreciated.
You might get away with it.
That's quite a jump down, though.
You might experience oil return issues, due to line sizing.
What killed the old one?
I am not sure what killed the last compressor, I do know that for the last two years that compressor was sounding funny as it was running. I would guess maybe bad bearings, but it did progress to a total burnout. The gas it contained when recovered was very acidic.
It sounds like you might have had lubrication issues with the old one.
Playing with sizes is done under controlled conditions, with new, clean systems, and watched over by several techs & engineers.
I see from your profile, that you are an engineer, so I guess you don't need a lecture.
It's your unit.
I can't say what SEER it will produce, or how many btu/hour, but worse things have been attempted.
You might wind up with a very high efficiency unit, or anything less.
Results WILL vary.
Put a suction drier on it, and monitor pressure drop.
Don't expect it to outlast the original.
I say give it a try!
The piston size will have to be reduced to match the new comp. Looking at the piston size used with that comp in the 13 SEER equipment will get you in the ball park. For example Goodman uses a Copeland ZR32K3-PFV comp in their 3T 12 SEER and I believe 13 SEER units which is a 32k BTU comp and calls for a .074 piston in the AH for cooling mode.
Reduce CFM through AH to around 400 cfm/t and carefully check SH and SC. When you dial in your SH you should have around 10F SC. If the piston size is too small you will have a SC higher than 10F when the correct SH is obtained. If the piston size is too large the SC will be lower than 10F with correct SH. If the piston is much too big like the one that is in there now might be, you may not have any SC because the smaller comp. may not have the capacity to provide that large of an orifice with a solid liquid column. Max. eff. occurs when you have just enough SC to provide a solid liquid column to the piston when SH is properly adjusted. SH= 10F measured at the OD unit is a good number for most apps. that don't require very long linesets or high vertical lifts. Let us know what happens!
If you could change the piston...
An old 42k burnout system and you want to replace the compressor with a 30k? I'm with the replace the whole system crowd.
Aw, you guys take all the fun out of it.
Anybody can do the right thing & replace the entire system, plus ductwork.
This guy is an engineer, and wants to engineer something.
It's a learning experience to spend good money after bad.
How come nobody mentioned TXV?
Thanks for all the input. If I was doing this for someone else other than myself, I would, without hesitation just replace the whole unit. I was basically given this old unit and am planning on putting it in a piece of rental property that I own, that does not have any unit it it now. Yes, I guess I will admit that I do want to engineer or experiment with this system. I figure the most I can lose is the cost of a 30K or 36K scroll compressor. If this doesn't work out then I can go back with a 42K recip. or for that matter just install a whole new contractor grade (i.e. Grand Air, or Comfort Aire) unit. I was attracted to use this Bryant unit for the additional bells and whistles that a higher grade unit will afford me. Thanks again for the replies. I will keep you guys informed as to how I come out.
Where's the fun in a TXV?! That's the easy way out. We want to experiment with a handful of pistons until we get it just right. Then do it again for the heating mode.
How are you going to learn anything if you just install a new matched system by the book? The factory already has everything figured out for you. You know it's gonna work. No fun in that!
I say go ahead and re-engineer it with a smaller compressor. What is the worst that will happen?--->Lose the compressor right in the middle of July? Then you got hot po'd spouse.LOL!