Is my new A/C the right size?

Question

My brand new 3 ton Gibson is barely cooling my 1850 sq foot second floor condo (with15 ft ceilings) - it is a 2nd floor condo/carriage house. The A/C manager said it should take 45 minutes to drop from 80 degrees to 79 degrees at 4 PM???That does not sound right. I live in florida. It blows cool air but not cold air. The ducts were not replaced. 3 days after installation I called back to tell them it was not cooling, they came out and said the Freon was not right so he "loaded it up again". It worked for 3 days, and then the weather became very humid and hot, and the ac stoped working well. It is very humid inside. The return duct is located in the coolest part of the non-haulted hallway,below the thermostat.

Answer 1

Your unit is undersized. Should be at least 4 ton.

Answer 2

I think rule of thumb is 1 ton per 1000 square feet. I think your unit is off and the temperature drop across the coils is not low enough. The unit is not balances or is low again on freon and you may have a leak. They do not use freon it is leaking somewhere if they had to add more. If the temperature drop across the coils is not low enough it will not squeeze the air to remove humidity. They need to come back and fix it and fix it correctly. If they come to you with this it was low on freon tell them to fix the leak.

Answer 3

Was a Manual J load calculation performed by the installing company? Just guessing the size of equipment by Rule-of-dumb square footage is incorrect.

It can take awhile for the a/c to cool down the house at 4pm if it was left off all day. Heat and moisture builds up and must be removed.

There might be a refrigerant leak if it worked ok after filling it up. Ask them to look for one if they say it needs more freon.

Answer 4

thank you Robert C...... finaly somene else who knows what they are talking about...

let me add that there are many things to consider for the situation at hand:

1. you are in an upper floor unit, heat rises so does the heat load that an ac unit has to account for, to perform its designed job

2. you have 15 foot high ceilings, plenty of space for heat and humidity to build up

3. the ductwork may not be adequet for a 3ton system or a bigger one for that matter

4. 3 tons of cooling is no way enough for your situation, to properly dehumidify, and ultimately cool the home, from what i can tell rule of thumb would tell me 3 1/2 or 4 tons, and thats square footage only + the addition of ceiling height and the fact you are in a second floor unit. basically rule of thumb is nothing more than a guess

5. a proper heat load calculation which any professional company can do for you would show the solution for your problem, and show exactly what your home needs as far as heating and cooling requirements

6. a goodman a/c, is only as good as its installation, even the best product can under perform if not installed correctly, and vice versa, goodman on a performance and reliability stand point is bottom of the barrel as far as the hvac market goes..... i hate to say this to you, but ya get what you pay for

now this all being said:

call a proper hvac contractor, i recommend an american standard customer care dealer or trane comfort specialist dealer, they are trained to perform a load calc, can measure the duct work for proper sizing to handle the proper size system for your home and they will give you a proper comfort consultation to address all your concerns, and finally make you happy and comfortable

also find a dealer in your area, that is n.a.t.e certified, the nate certification, holds the tech's and installers to a much higher standard than just the state license does, in other words you will 99% of the time get the best of the best when it comes to hvac, when you look for nate certification

Answer 5

The rule of thumb is actually 1 ton per 500 sf.  

So 3 ton unit would be for 1500 sf.  But that is assuming normal ceilings.  You have 15 ft ceilings.  That is a lot more space to cool, than normal 8-10 ft ceilings.  So 3 tons might be bogged down.

But you said it worked for 3 days, so you know it can do the job....but said it didn't work so well on very hot/humid day.   It could be that the freon leaked out or it is just not capable of handling the high heat and humidity.  

It could also be your duct work, but more likely it is that the unit is simply too small to handle the job.

I would get tech back out to test the freon.  If it shows the same amount as it did after last addition, then the freon is not the problem.  

I will say that no properly working system should take 45 minutes to drop the temp one degree.  My unit will drop from 76 to 72 on a very hot/humid day within 45 minutes... and that is 2250 sf on a 3.5 ton geothermal unit.  Too small in my opinion, but will freeze you in most areas of the house.

Also, you say it blows cool air, but not cold.   It should be blowing out air that is high 50's low 60's.  And should be pulling out air that is at least 15 degrees higher than that.

I would definatley keep after the A/C guy until a problem is found, or it is determined that the unit is simply too small - hope for a problem.

Good luck.