thegunsmith2506 Report post Posted June 4, 2020 We have an 1800sqft house with a 5 ton A/c unit in northern AZ. My wife likes to keep the windows open all day until it starts to get hot and then shut everything and turn on the AC to cool the house off in the afternoon. The A/c will usually freeze up within 20min of turning it on. The unit is only 4 years old and probably only gets used for a couple of months a year. We had the company that installed it come out and check everything and they said it looked fine but left before it froze up. The little reading we did online lead us to believe that the unit might be too big for this size of house. Also, our outside temp almost never gets above 90deg. Do any of you HVAC guys have any suggestions on what it might be? Share this post Link to post Share on other sites
Delw Report post Posted June 4, 2020 A/c's freezing up are caused by one of 2 things. Low on freon return is blocked, either by filter, dirty evaporator coil etc etc. 1 Share this post Link to post Share on other sites
PRDATR Report post Posted June 4, 2020 Definitely check the filter. Rule of thumb here in Phoenix is to replace them every 30 days on home units during the season. I also put the date on it with a sharpie. Share this post Link to post Share on other sites
Delw Report post Posted June 4, 2020 Didnt read the part of being too big. a 5 ton on 1800 SQF I highly doubt it. a extra 1-2 tons is not that big of a deal. its all about airflow a higher tonnage with require more airflow as it has bigger fans. so if nothing is dirty and you got good airflow open a few windows in the house that will give more airflow. I highly doubt that is the case. also a newer unit shouldn't need Freon if it does the its leaking somewhere. usually the shrader valves the seals coould go bad but this only happens if someone checks the freon all the time with gages. One thing you didnt say is if this is a split unit or a package unit. if its a split unit they might have not solder the joints good enough and you have a small leak.(that does happen often) Package units there is no soldering its all done at the factory so chance of that is very slim(unless again someone check pressures with Gages. My old home gettol unit lasted from 1982 - 2010-2014. only reason it was replaced cause it rotted out. I never put a set of Gages on it and when I quit the field back in the 90's I never let anyone put gages on it. it only blew one condensor fan motor and 2 contactors and a relay. it was hit by lightning once. where fighting and opposite issue here at the shop. dang thing wont cool down past 84º runs 24/7. The unit is brad spanking new (few months). once we hit a temp of 98 degrees outside it just wont work right Ie wont go below 84º. But I am thinking its a duct problem return in wrong place and vents in wrong place or they put too little tonnage on it. There coming to look at it tomorrow again. 1 Share this post Link to post Share on other sites
Hoss50 Report post Posted June 5, 2020 Its an airflow restriction or a low on freon most likely as mentioned above. A 5 ton on 1800sqft in northern AZ is probably too large, but they problem that should cause is short cycling which means the unit cools the house so fast it turns off quickly which isn't good for them. Check the filters and return ducting. I would have a tech check the unit out and check the refrigerant charge. You may also need to up your motor speed to try and move more air to help mitigate the problem. Most newer systems have indoor fan motors with between 3 to 5 speeds. You just have to move a wire on the motor to get more airflow or less. Share this post Link to post Share on other sites
Hoss50 Report post Posted June 5, 2020 The general rule of thumb for tonnage in houses in AZ is 400sqft/ton. That would put your loads at roughly 4.5 tons. Then add in you are farther north so you could likely get away with a 3-4 ton unit depending on layout and design. My house in Phoenix is 2100sqft with vaulted ceilings. We have a 5 ton package unit and it will keep our house at 74* or less all day if we choose. Share this post Link to post Share on other sites
PRDATR Report post Posted June 5, 2020 You are better off with an undersized unit that uses fewer amps on startup and runs longer to pull the humidity out of the air. 2 Share this post Link to post Share on other sites
muledeerarea33? Report post Posted June 5, 2020 11 minutes ago, PRDATR said: You are better off with an undersized unit that uses fewer amps on startup and runs longer to pull the humidity out of the air. Dam Michael Vick, I’m glad you gave an answer that is helpful. 1 1 Share this post Link to post Share on other sites
PRDATR Report post Posted June 5, 2020 8 minutes ago, muledeerarea33? said: Dam Michael Vick, I’m glad you gave an answer that is helpful. 40 years in the business has worn off on me. Share this post Link to post Share on other sites
