Using a larger condenser than called for?

[tom1843]

I have a 3.5 ton Unico evaporator and want to use a 4 ton condensor. Is there anything really wrong with doing this.

I know they should be matched. I happen to have a new unit and would like to use it instead of buying another one.

The high and low pressure lines will be about 75-80 in length. I have seen plenty of situations where the evaporator is larger than the condensor just don't know about this situation.

Thanks in advance for your replies.

[gillman-air]

High velocity air handlers such as unico are less forgiving. I suggest you use the correct sized unit.

[kfitts]

I was always told as as rule of thumb, to either match coil for coil or over size the Evap coil half a ton.
Please correct me if I am wrong but, If the Evap is smaller the the condenser, this would cause flooding the Evap and creating a freeze issue.

[tom1843]

Thanks for the reply. One last thing. A local AC tech said it would work if you undercharged and that the long lines would help.

I will stick with the 3.5.

[Gunnery Sergeant Hartman]

Is it a rated ARI match?

If not, look for problems ahead.

[tom1843]

I don't want problems. Thanks

[BaldLoonie]

As Dot said, use only an ARI match. Unico air handlers reduce SEER & capacity. While you think putting a 3.5 ton outdoor unit on a 3642 air handler will give you around 42,000 BTU, it could be considerably LESS!

[stef]

If you do this yourself for your own house, then I say go for it. 4 tons outdoor with 3.5 tons indoor - NO Problem if you at least put in an expansion valve. As for 78 feet of freon line, my recommendation is to install a liquid line shutoff valve to really stop the migration. You sure as heck don't get the sensible capacity. But you will do better on humidity. You can do 350 CFM per ton if you like -no problem. Your SEER is not good. But the systems should operate with no problem.

If you do this for a living, then I strongly recommend you to talk to the customer again a bout SEER. For this is a long term investment for the customer. Once you leave this customer, there will be other service guys who may say alot of things that will not be good for your reputation since you are not there to defend it.

[tom1843]

I did this installation in my own house I wouldn't do this for a customer. I got rid of the 4 ton unit today. The system has the 3.5 ton condenser. The actual length of the lines are 45-50 feet (I was planning on relocating the unit, thus increased line length).

I spoke to tech support today and asked btw what would happen with the 4 ton and they said no problem but you need to change the TXV valve. It will also work for the reason below.

At this installation, it was the first time a Unico was used. Well they shipped a 3642 coil but shipped a 4860 air handler in the wrong box. The installers didn't know (Or even seen one of these before)and put the system in. Yes they said the plenum adapter need some adaption. We had mismatch problems until we figured it out. It now works fine but not perfect. It wasn't returned because the sysytem sar for a year before install.

BaldLoonie, why do Unico systems reduce seer and capacity? If its not too much trouble I would appreciate an explanantion.

Stef, cna you explan, my recommendation is to install a liquid line shutoff valve to really stop the migration. What is migration?

Members, than you for your time and education on this matter.

TOM

[stef]

Tom1843,
It is best of course to install TXV in any system. Especially your mismatch sytem.

Migration of freon during the off cycle. Especially the fix flow rater type metering device. Freon will still pusing through the orifice and stay on your low side (evaporator). Thus, when your unit starts up again, the freon will flash (boil up). If you have long lines the too much freon will migrate into your evap coil. You compressor will have to pump that extra freon for very little gain of cooling for the extra KW that your compressor will use (not counting the flooding the compressor with liquid refrigerant). Therfore, stopping freon migration will tend to increase your SEER.

Some may say that non-bleeding TXV will shut off the migration too. But does it really. Why not be sure and shut it off with liquid line solenoid valve, which is not that expensive but the return is far greater.

Like I said, the mismatch system like your will do better on LATENT heat. But the SEER is not that great. If you live in the region of high humidity, and you do it your self, I say go for it.

Have fun

[maxair]

I put a 3 ton cond on a 2.5 evap coil lennox just change
piston size good delta t and humidity control.My undersanding if you go to far is you start to have
low suction press.

[beenthere]

HV systems have lower volume air flow, so they don't do as much sensible heat removal, as a conventional system, but they do much better at dehumidifing because the lower volume air flow allows for the coil to be much colder.

With the larger blower, did you add more outlets, is it noisey?

[BaldLoonie]

Also, HV systems have BIG blower motors which use more juice & put out more heat. All this is taken into consideration in ratings.

[beenthere]

Originally posted by BaldLoonie
Also, HV systems have BIG blower motors which use more juice & put out more heat. All this is taken into consideration in ratings.

Knew I was forgetting something.

[hvac-tech-lane]

Unico:
200 cfm per ton
30 deg delta
30% more latent capacity than conventional
Much larger coils with factory installed TXV's
Follow their rules they don't take well to cheaters.

[klyons20]

match conderser with a coil.. It that simple..

regars,
Kelvin

[tom1843]

Thank you all for the information. The unit is matched and working fine.

[PullaVac]

Don't know much about Unico, but I have learned over the years, that with the conventional AC split systems,(those that are missed match,larger cond. than coil) you can do best by balancing the system with the Temp. difference across the coil. The gauge readings will not necessarily give you a true reading. I was taught to use the TD across the coil and try to get maxium difference of TD by adding or removing refrigerant,this has worked well with flowraters or metering devices. I have been able to get good performances out of systems that had been mismatched and overcharged by using gauge readings only. Many times, I am sure, some techs don't bother to check the coil size before charging a unit. Most of the mismatched units, I have found on rent houses.The landord wants the cheapest way out and some jackleg will put whatever he has on hand to make some extra money.