Old 10 Seer Coil and new 13 Seer Cond- OK ?

[g2345w]

Lennox 4 ton 10 Seer compressor has failed. 10ACB48-5P 1997
Can I install a new Rheem 3.5 ton 13 Seer condensing unit?
The Coil is Lennox 4 ton 10 Seer CB29M-51-1P with a balancing valve. Thanks.

[davefr]

Most of the pros will tell you to change HP and Coil at the same time. It's not wise to try and salvage an old coil during a HP failure.

For piece of mind I'd do coil + linset + HP.

If the compressor self destructed you could have contaminents thruout the system.

[comfortdoc]

Originally posted by g2345w
Lennox 4 ton 10 Seer compressor has failed. 10ACB48-5P 1997
Can I install a new Rheem 3.5 ton 13 Seer condensing unit?
The Coil is Lennox 4 ton 10 Seer CB29M-51-1P with a balancing valve. Thanks.

Indoor and outdoor systems should be matched for max efficiency and reliability. It is highly likely that you will experience compressor failures in the future that can be directly contributed to the mismatch. There will be no Rheem warranty on the outdoor unit if the indoor is not a rated match. Change the system in it's entirety.

[mrfixit-ms]

I concur with above posts. You did not state how compressor failed. ) a system replacement should be MATCHED PERIOD. Why send money to achieve eficiency and destroy it with a mis-matched system?


I'm just old not senile

[mark beiser]

Hey guys, its not a heat pump, its straight AC.

Ideally you should change both, and considder going to a heat pump.

The CB29 air handlers were not strictly for 10 SEER outdoor units, and it is even on the list of indoor units Lennox says it is ok to match several of thier current outdoor units with.

I know some here don't agree with the practice, but with a straight AC condensor, correctly installed with filter driers and proper evacuation, and a TXV in the indoor coil, the system would work.
It probably won't be 13 SEER, and may be just a little less than cooling capacity than with a matching indoor unit, but it will work. There isn't really any reason it would be less reliable either.

It gets a bit more sticky with heat pumps. If you want to have a heat pump outdoor unit installed, but are not in a position to change the indoor unit, you should stick with one of the heat pumps Lennox says it is OK to match with that air handler.

I'll probably catch some heat for the above statements.

[tinknocker service tech]

i agree with mark on this
even tho a matched system is the idael way to go
the cb29 i blieve came with a factorie installed txv
if it didnt then have one put in

[g2345w]

Yes Mark, the local installers say they frequently install new 13 seer condensing units on old 10 seer coils, just as long as they have a TVX.
What do you think of dropping from 4 to 3.5 ton on the condenser? The load calc says 43,000 and the system cycles off even on hot days. Does this help or hurt the mismatch?
Does anybody know WHY the compressor could fail? Any comments on pressure, humidity, or cfms? Thanks to all of you for your comments, George.

[mark beiser]

43,000 btuh eh? That the total or the sensable? The sensable load is the important one when it comes to picking equipment.

Most compressor failures are caused by contaminants in the refrigerant, poor indoor airflow, other installation problems, or a combination.

[g2345w]

Update from George !

Existing Coil- 4 ton 10 Seer
Prooposed Condenser- 3.5 ton 13 Seer

http://www.heatload.com says 43,727 TOTAL btu.
Sorry, No breakdown is given on sensible vs latent.

We're in South Padre Island, Texas and as you might guess, summers are hot, humid and long. It's 9:27pm and 72 degrees. Bet you wish you were here, as we got 7 nice trout today.

Heat calc stats- Frequent high 95. Summer low 77
Frequent low 45 Winter high 73
Temp differential 20 (75 degrees)
Grains 63

We'd like the system to run more for more stable temperature and lower humidity. Mismatching the SEER will reduce efficiency?, and mismatching the size will give longer runtimes? How does this mismatch effect the humidity issue?

[comfortdoc]

There could still be warranty issues connecting a Rheem condenser to the older Lennox A/H. If Lennox has ratings for this indoor unit with 13 Seer outdoor your best option in the long run would be to stick with Lennox. The technician onsite would have the best information available to offer an educated guess on the cause of the compressor failure. Low airflow, lightening strikes, loose wires, short cycling, refrigerant undercharge or overcharge, bad capacitor, poor installation practices originally etc. are some conditions that could have caused compressor failure.

Using your load calc have the system capacity matched for sensible and latent loads. You will be happier when it's 95°and 95% humid.

[comfortdoc]

Pay the $50 and use HVAC-Calc from this site. It will give a breakdown of sensible and latent loads.

This is a dilemma with mis-matched systems. You are guessing at efficiency and capacity split.

[beenthere]

The 3.5 ton condenser may not be able to get the indoor coil cold enough to remove anymore, or as much moisture as the 4 ton did.
Can the indoor blower be slowed down.
Have to be carefull not to slow it sown too much also.

[docholiday]

As others have metnioned, The problem with mismatching straight air is you dont know what capacity you will get. The system determines this, not just the outdoor coil... SO what if the homeowners system barely kept the house at 95, and your frankensystem loses 2-3k btuhs? You gonna sit there and warranty parts and labor trying to get it to work? Slowing th fan might make up latent, but it will reduce sensible. I wouldnt even try to guess at what you are starting with.

What are you going to do if the efficiency actually drops? And yes, it can. If you end up with a system that costs more to run than the original system, you will have to somehow explain it.

Be a pro and offer a proper solution.