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My Thermostat and my independent thermometer constantly read 3 degrees differently. Set for 70, thermometer reads 73. Set it for 67 in the winter it reads 70.
Oh well, they were calibrated differently. I just set the thermostat 3 degrees below what I want the room temperature to be. Problem solved.
If your area is experiencing a heat wave sometimes these ac units just can’t reach the desired temp.
My unit is 5 years old and even with the blinds/shades kept closed, by evening my thermostat reads 77-78 while it’s set for 74. Our daytime feels like temp has been above 100 for the past few days.
Get a laser temperature gun and check the output temperature at the registers. In addition ... if the duct work is in the hot attic then that will contribute to thermal gain inside the duct work.
20* temperature drop across the evaporator which usually manifests as 15* difference at the register. So... if the room is 79* the air coming out the vents should be in the mid 60's*. Anything less than 10* drop from ambient room temperature and you likely have a problem.
/\ Worth repeating. Laser thermometers are cheap and very, very useful.
If you are getting the 15 degree temperature drop, that shows the AC is actually working properly. But now it gets a bit complicated.
Air flow is everything to an air conditioner. If the unit is old then the evaporator coils (that's the inside part) could be clogged up and not let enough air through. Generally, the age of your unit can be checked by looking at the serial number on the information plate. Generally, the last 2 numbers are the year. I just replaced one that had been in place since 1987.
Then there is the question of whether the unit ever shuts off. If it never shuts off, then it - for one reason or another - simply cannot cool the home.
Check temperatures with another device, both at the thermostat and various points in the house. Out stat is in a foyer by garage door and attic door which tends to run a few degrees warmer than rest of house. So we adjust settings accordingly. If we want it 77 in the living room then we set it to 79. But generally we set it to feel not a number.
1. Was the unit running when you checked the temperature?
2. Is the thermostat thermometer independent of the dial setting? Some thermostats have a bimetallic thermometer that has nothing to do with the thermostat control. Some models can be calibrated by using a calibrated digital thermometer and a small thin screwdriver.
3. If the unit was running and the temperature was accurate then either there’s something wrong with the unit or there’s something wrong with the apartment. I once lived in an apartment that had inadequate AC capacity for the amount of heat coming in from the single pane plate glass windows facing west. There once was a tree to provide shade but the tree was removed.
4. Landscaping could also be an issue. What is the condition of the lawn around the condenser unit (the part of the AC outside)?
5. The coils (both inside and outside) may need a full cleaning.
1) Actual temp and temp reported on the face of the tstat are different. This is just a calibration error and doens't need to be fixed unless you really want to.
2) AC is unable to bring the temp down to the tstat's setting. That's just because it can't remove heat as fast as the house absorbs it. First step is to make sure the unit is working the best it can (clean condenser, fresh filter, no crimped or blocked ducts, fulll charge of refrigerant). Second step is to reduce heat uptake of the house (insulation, sealing around doors and windows, reduce solar load with a white roof, awnings on south/west facing windows, you all know the drill. Third step is to put a higher capacity AC, or alternately learn to live with it in the hottest part of the year.
It is often dependent on thermostat location. My ac thermostat is set to 78. It is located in my great room (kitchen, dining, living room combo with cathedral ceilings) and it keeps that area right at 78. The thermometers in the 3 bedrooms read 79 to 80 with each bedroom having two external walls. Close enough for me. Ceiling fans can make all the difference. I have 4 in my house. One in each bedroom and the great room. I rarely use the fans.
O.k. AC vendor came over. Unit is running fine. Air blowing up from the return in the hallway is 78.6. AC supply going is strong: 54.6
Evaporator coils were dirty but not too bad. I thought the AC guy who came by last March in addition to the condenser coils cleaned the evaporator coils as well. Apparently not.
While inspecting the unit today the AC tech noticed the indoor fan motor speed was set to low. He said the installer who put in the unit 3 years ago should have set it to high given this is AZ which doesn't have much humidity.
I said fine. Please set it to high. I was then told there should no problems cooling the house to 75-76.
(3.5 ton package AC 1500 sq ft home)
Renter will be home tonight.
Hopefully this will be the end of it and when the AC is set to 78 the thermostat will read 78 as well.
I just dealt with this issue this weekend at a rental house that I own. Tenants couldn't cool the first floor below 79 degrees no matter what the AC was set to. Called an AC company out and they couldn't find anything wrong- system was running fine. The conclusion was just that the system was old (it is- 20 years) and has lost capacity over the years. They also identified some ductwork design issues, but that can't be the issue because it has worked fine for 20 years.
I was about ready to bite the bullet and buy a new system, even though the AC company said it might not fix whatever the issue is. However, while I was there I saw a bunch of weeds surrounding the outdoor unit. I pulled them all, not thinking it mattered- just because I happened to be there. I also dropped off a window AC unit to hold them over until I could get this sorted.
Lo and behold, it turned out that it was the weeds that were causing the problem. I was surprised because they weren't touching the condenser, but I guess created sort of a heat umbrella around the unit. They were sort of like mini trees- about 5 feet tall all around and above the condenser, but a good 3-4 feet away from the condenser. Today they called me and said that they didn't even need to turn the window unit on, and that the system was able to hit 70 degrees (it's 91 degrees outside).
Yep, I spent 20 years in automotive AC, people tend to underestimate the importance of condenser performance. It's the single biggest determinant of AC system performance and life.
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