Search the forums

Loading
Home › Forums › Breaktime › Energy, Heating & Insulation

Make any sense to use a used (free) central A/C unit?

Mpls1921's picture

Make any sense to use a used (free) central A/C unit? (post #193931)

Mpls1921 on Tue, 09/28/2010 - 14:29 (updated 09/28/10 - 09:04) 
in

My parents are having their forced air furnace replaced due to some cracking that the current one apparently has in the heat exchanger.  They are getting a new AC unit at the same time "because it's cheeper to do it at the same time".

My house has a central AC unit (Coleman Presidential II) that appears to be from the 80's.  The many of the fins on the unit are substatially bent.  When it turns on, I picture the scene from Christmas vacation and Clark powers up his lights (and the power company powers up the Aux Nuclear Reactor).

My parents current AC unit is from the mid 90's and has a scroll compressor.  It is a 2.5 Ton unit, I don't know what I have on my house now but when I got a quote from a Trane dealer in the neighborhood, he quoted me for a 2.0 ton unit ($2700 for a 14 SEER).

I was sort of thinking to myself, :Self: what if I took my dads old unit and had someone install it at my house."

Probably doesn't make sense, but I just thought I would throw it out here for some comments.

 By the way, my $1500 energy tax credit is almost used up already from some other things, so that is not a factor.

Thanks

Erik

-A +A

Might make sense.  But you (post #193931, reply #1 of 5)

by DanH in reply to Mpls1921 [original] on Tue, 09/28/2010 - 18:38

Might make sense.  But you need to have the guy who suctions the old system and removes it properly seal the pipes to protect the unit.  And also you need to remember that the compressor unit and A coil are matched -- if possible you should remove the A coil and install it in your system to maintain the match.

But keep in mind that a 2.5 ton unit may be oversized for your house, and it's worse to have the unit be too large than too small.

(Back in the mid 40s when the ENIAC computer was being built in a basement at the University of Pennsylvania they had to warn the power company before they powered it up.  (It contained 17,468 vacuum tubes))


We are like tenant farmers chopping down the fence around our house for fuel when we should be using Nature's inexhaustible sources of energy -- sun, wind and tide. ... I'd put my money on the sun and solar energy. What a source of power! I hope we don't have to wait until oil and coal run out before we tackle that. --Thomas Edison

Unit size (post #193931, reply #2 of 5)

by JTC1 in reply to Mpls1921 [original] on Wed, 09/29/2010 - 05:11

Take this with a large cube of salt since sizing of A/C units is certainly not a strong point of mine.

DanH brings up a critical point - your Trane buddy presumably did the sizing calculations and arrived at a 2 ton unit for your home.  Your parents "free" used unit is 2.5 ton, a 25% larger unit, but probably more energy efficient - guess based on age alone.

Humidity in your area would be the prime consideration -- the effect of a "too large" unit in a humid climate is that the unit cools the house too quickly and thus does not remove humidity effectively because of a too short cycle time.

If your climate is dry, the larger unit will probably be OK, if you live in a humid climate you will end up with a cool, but clammy house with an oversized unit. Completing your forum profile would help.......

Might want to get another opinion on the sizing.

Jim

Never underestimate the value of a sharp pencil or good light.

By the way, if you can find (post #193931, reply #3 of 5)

by DanH in reply to Mpls1921 [original] on Wed, 09/29/2010 - 05:29

By the way, if you can find the nameplate on your unit and it isn't too badly faded it will likely quote its tonnage and SEER.


We are like tenant farmers chopping down the fence around our house for fuel when we should be using Nature's inexhaustible sources of energy -- sun, wind and tide. ... I'd put my money on the sun and solar energy. What a source of power! I hope we don't have to wait until oil and coal run out before we tackle that. --Thomas Edison

What refrigerant is (post #193931, reply #4 of 5)

by Amish Electrician in reply to Mpls1921 [original] on Wed, 09/29/2010 - 12:40

What refrigerant is used?

IMO, it makes NO sense to re-use a unit that was intended to use something that will become obsolete in, say, the next ten years.

Moreover, there has been a significant improvement in efficiencies (SEER) over the past five years - so you may be better off with a new unit anyway.

I had considered the (post #193931, reply #5 of 5)

by Mpls1921 in reply to Amish Electrician [original] on Wed, 09/29/2010 - 18:07

I had considered the possiblity of short cycling.  I can't seem to find the ton rating for the current unit, the tag I found gives the draw for the compressor and fan, model number, etc, but I don't seen anything about the capacity.  given the condition of the unit, I'm not sure it is exactly relevent anyway.  When it's hot enough for me to use it (90+F), it runs pretty much constantly.  Humidity is a factor here (Minneapolis, MN).

I have no idea what it would cost to transport it to my house and have it installed.  Given I can get the 14 SEER new unit for 2700 and the 13 SEER unit for 2400, I don't think it would be a good idea if it cost me more than say $500 in labor to install my dads unit.

SInce I only use it when its really hot/humid, I am leaning to dropping the idea, and just sucking it up and paying for a new unit when the current one bites the dust...

 

Thanks for the comments, always very much appreciated.

 

Erik