AC, Heat, Thermostat. What might it be?

Question

Tenant informed me that the temperature would not fall below 79 degrees even at night (they have it set at 72). It's humid and ridiculously hot right now in MD (100+ degrees). At first I thought that was because the tenant is enrolled in the Peak Rewards Program that allows Electric Company to control the AC  during the peak hours. (They called the Electric Company and even spoke with the Honeywell People (thermostat manufacturer) to make sure it's not the settings). Anyway, I am about to call the AC guy...
Any idea what it might be and what it might cost???

Thanks in advance!!!

Joel Owens · Answer

When is the last time the outside unit was serviced??

There is the coolness of the air and then the air flow.Is the air flow reaching all vents properly??

If you have adequate air pressure and size of run returns then look at coolness. Is cool air blowing through the vents??

What type of air filter is the tenant using?? Are they using an expensive micro particle one?? These are great but need to be changed more often than the cheap ones.They catch more dirt but also after awhile cause air flow to suffer unless they are changed regularly whereas the cheap ones will let more dirt through the filter but will stick to the fan motor.

For this reason we use the cheap ones and change out for the tenant once a month so we know it's changed.The unit being 8 years old check the outside unit.Make sure there is air flow to coll the return air properly.Take a dollar bill while it is running and hold it up against different parts of the coil and let go.The air should suck the bill to the coil.If there are places where the bill won't stick and falls down you need to straighten the coils and also take a hose with water after turning off inside and at the outside switch and clean the coil.

Then restart up and use the dollar bill around the coil and if it sticks you have much better air flow on the return air.Check the free on level first as well. Doing these things you should see an improvement.

Having said that here it has been really hot as well 100 and my a/c at peak it will get 78 inside during the day.If it was 90 or 92 I wouldn't have an issue.I would love to have it at 72 all day long as I am warm blooded.Can't wait for the hot weather to go away.

Marc Freislinger · Answer

I would second the icing issue. If the unit is low on freon, and it's humid, the unit will ice over. The only cooling then is the fan blowing air over the ice, which can actually keep a unit a bit cooler than outside.

If it just needs a charge, it usually $25-$40/lb depending on what you can negotiate. Plus a trip charge.

This is assuming you've already checked that the outside unit is running when it's trying to cool. Otherwise you can check your T-stat wire running to the unit (gets hit with weed wackers). On a 9 year old unit, your contactor might be going bad as well. But neither of these are worth looking into if the unit outside is actually running.

Also keep in mind, depending on where you live, A/C units are sized to cool approx 15-20 degrees cooler than outside air temp. In areas that are not used to high temperatures, the unit just might not be sized right to account for the higher temps.

James Martin · Answer

Remember if it is very humid during the day or at night, the unit will almost never reach 72. The unit will be working hard trying to get the humidity out of the home.The new High Efficiency air conditioning units may be partly to blame.The Manufacturers use a smaller compressor with a larger outside coil and inside coil to get more efficiency out of the units.This cuts the dehumidifying capacity of the equipment way down.Humidity in our homes is a major concern in our climate.  If you have to turn your thermostat below 74 degrees in the cooling mode to feel comfortable, then you have a humidity control problem.

Lisa Lunger · Answer

I had a rental with the same issue and the air filter was really dirty.  That caused the unit to ice up and not cool very well.  Once the unit builds ice, it needs to be shut down for a few hours to melt....

Mitch Kronowit · Answer

I always perform two simple tests when checking out an A/C system. The first is temperature drop. Using a thermometer, measure the air temp at the return (where the air enters the evaporator/blower unit) and also at the register (select one close to the evaporator). The difference should be around 25 degrees. IOW, the A/C system should be able to take the air in one end, the return, and spit it out the other end about 25 degrees cooler. I like using my touch-less IR type thermometer that you simply point and "shoot", but before I was using a digital thermometer with similar results, just a little less convenient, especially if the register is up high requiring a ladder or something.

The second test is for airflow. I don't have any fancy equipment for this, so it's more a subjective test, i.e., I can't measure cubic feet per minute of anything, but I will hold up a small strip of paper, about 1/2' by 8 inches long and the air flow should make it flap around. If it barely lifts from the surface of the register, there is some kind of air flow obstruction (too many registers wide open, dirty filter, iced up evaporator coil, etc.).

If either test fails and I can't resolve it, time to call the HVAC guy.

Jon Holdman · Answer

Even with the recharge your AC may have tough time getting from 100 degrees down to 72.  That's a LOT of work, and it may just be beyond the capability of the unit.

Be sure to use those ultra-cheap filters in the summer and change them frequently.  Good airflow is essential to good performance and those expensive filters can be too restrictive for the AC.  OK for heat, but not for the AC.

Robin Grimes · Answer

What is the attic insulation like in the House?  If it's an older home, blown in insulation is a fairly cheap way to increase the efficiency of heating and cooling.

George P. · Answer

Thanks, I will let them know

George P. · Answer

Just to update, the condenser needed cleaning, and freon needed recharging. Paid $120
Thanks all for the tips!!!

AC, Heat, Thermostat. What might it be?

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