I was thinking of replacing my outdated 5 Ton Airquest Central AC: Model NAC060AKA1 Ser.# L021909682 outdoor unit that is part of a Space-Pak system I have that I've read much about (mostly bad unfortunatley) and will not be easy to retrofit or change because of the water heat set-up in my home with NO duct work.I have no idea when this outdoor airquest unit was installed (10 years plus would be a guess)and can not seem to find the seer rating for it....10 or lower would be a guess...maybe someone knows....I just know the system costs me a LOT to run because of the way it was installed...with only ONE return for air for the air handler it should have been installed in the atic but because of the design of the house (Barn Gambrel Style)there is not an atic AND they mounted it in basement ceiling AND even put the return air drop down there instead of at least pulling the air from the first Floor area (I will say that my basement IS finished and I DO keep the humidity at 60 or lower so it's conditioned air it's pulling)...unbelievable to me...soooo...as I basically blow cold air into a hot envelope I find that if I run the fan continously it actually keeps the temps on the two levels very close BUT struggles in very hot weather and basically costs me fortune to run in hot weather which we are currently experiancing. I live in Michigan so it's not that common and I have lived with the systems short comings for some 10 years now since purchasing the house but find I'm always thinking about how to help retro-fit/improve it AT the most economical costs. Obviously R&R the whole system would be quite expensive and I have considered these split systems that are mounted thru the walls in order to get the heat out of the top of the house which has to be absolutley necessary I would think to having a good system but my house isn't quite the OPEN plan that these would work best in.I had my air handler motor in the Space-Pak High Velocity out recently (it was shot) and rebuilt and feel comfortable that it may have long life yet especially with me running the fan continuosly instaed of going on and off....considering the cooling coil well I don't know what it's life may be but is very old (do I have to worry about that going bad?). The outdoor unit (the airquest unit mentioned above and not original to the system) is the other consideration and I was wondering if it might be advisable to consider replacing that with say a 2004 Trane 5 Ton 14i with a seer of 15 that some one changed out when going to a heat pump set-up that I could get a good deal on (600$)or something similar (this may be the cheapest way for me to save some $ running it without going to the expense of R&R the whole system and considering the Michigan climate might just make the most sense) and if so when looking at something like this what should one be concerned about? say if the unit has been sitting with NO freon is this a problem? is there a proper way to store these? etc...and because of my high velocity space pak system do I need some kind of special outdoor unit? also if someone might know the seer of the airquest unit I have...please let me know even if it a guess...I can't seem to find it or the mfg. date on the info plate.Of course keeping this airquest set-up that IS still working fine might just be what you all recommend until it basically breaks BUT thought I would get some thoughts/advice about that question. Thanks for ANY advice or comments as I value the forums greatly.