Matching condenser with existing coil

[TomFitz]

A friend's residential A/C unit (compressor) went bad. He had a 4 ton system and his brother offered him a 5 ton 13 SEER condenser (free) to replace the bad one using the existing coil (matched for the 4 ton unit). I advised him to replace the coil as well, but his brother didn't have one and stated this would work just as well.

Can he use the 5 ton condenser with a coil rated for 4 tons?

Thanks for any info..

 

[mechanicaldude]

I would pose that question more to the manufacturer of the equipment. I'm guessing they'll tell you its not recommended to do this. You're better off using a 5 ton coil with a 4 ton condensing unit. I think in the cirumstances you've described you might be concerned with the refrigerant pressures running too high but you definitely will not get 5 tons of cooling out of the unit. The best thing to do as you said is to just just apply the savings of the free condensing unit to buying a new larger coil with it.

Have your friend call a Trane or Carrier rep or whoever's equipment it is, I'm sure they will not recommend doing this and you'll probably even void any warranties that came with the condensing unit.

 

[TomFitz]

Yes I agree, I don't think he wanted to get 5 tons of cooling out of the unit. My concern was that using a 4 ton coil with a 5 ton compressor may void the manufacturers warranty.. and sure enough, when he showed it to me today, the warranty stated that it will only cover the warranty if installed with their matching coil.
He is now ordering the 5 ton coil to be on the safe side...

 

[rmw]

TomFitz,

I know from other postings that your day job is in the power industry or similar. The 4 ton coil with a 5 ton compresser is equivalent to your trying to run a condenser from a 400 MW unit under a 500 MW unit. It would work, but it just wouldn't have a very good back pressure.

The smaller coil would result in a higher condensing pressure and the cycle would be affected accrodingly.

rmw

 

[TXiceman]

rmw, if the coil is a 4 ton and the condensing unit is a5 ton, it will balance at a lower evaporating temperature and provide something between 4 and 5 tons. The lower suction on the condensing unit will be a lower capacity at the compressor and result in a lower THR to the condenser and a lower condensing pressure than the design for the full 5 ton load.

In order to keep a efficient system, I'd recommend a better match on the low side and high side units. The 13 SEER rating is out the window unless matched properly to an evaporator.

Ken

Ken
KE5DFR