All of a sudden our upstairs AC just isn’t working like it should. It’s not as efficient and the upstairs just isn’t cooling like it should.

-coils are perfectly clean
-Freon or whatever these days is good
-basically mechanically all seems good
-Units are new (4 years basically

It seems to nose dive with humidity more than heat.

Yes I know it’s been hot in the south but it’s not the hottest it’s been since I have been here and something is off/changed this year.

Today we had a storm roll through, humidity shot up, cooling went to shit. Basically 75-76 outside was not struggling for 73 upstairs.

Later on unit is cooling “ok” again.

I feel like maybe there is a duct work or insulation issue more then a mechanical one. I have one vent in a bathroom condensating more than usual but that could be hot year/days.

Any ideas??? Unit and ducting are attic mount for second floor. 1st floor more or less fine.

I just know so very little about HVAC/Home Ventilation/Insulation that I don’t know where to begin. It’s one of the few areas I cannnot muster up any knowledge about.

So what say ye? Any ideas, things to look for, tools/sensors to use to test or diagnose?

As always thanks all,
Chris

Have you checked the pressures when the unit is cooling well and again when it is struggling ? Also check for a leaking plenum or duct .

Either improper or inadequate return air or improper sized system for your area.
Call a good AC guy to have it checked out.

Not sure how you came to conclusions that coils and Freon are good, did you test with gauge set? Did you cut open the coil box and check?

If you think it's the ducting, first check filters, then check return for gaping holes. AC should be cooling intake air by about 20°. So if you're sucking in warmer sir that could cause it. If it's damaged supply lines that should only affect one or two rooms usually.

Did you have anyone in your attic doing other work - electrical, data lines, insulation, etc?

Do you have a thermometer that you can check return and supply temps? Are you able to check for crushed or torn ducts?

Step 1; Check the filters. 9 times out of 10 when we get a call on a unit blocked air (or water on water-cooled) is the culprit. Cottonwood, insulation, heavy dust buildup, leaves, etc. The outdoor units have screens on the outside of the unit so it's easy to clear off large debris. I'm not familiar with what a home attic unit looks like.

If air isn't pulling hard on the suction side, like holding paper to it, or if the fan isn't blowing a solid column of air, you've got blockage in the coil or filter.

Step 2; check the supply conditions. It may be 75° outside, what temperature is your attic, or wherever air is being pulled to cool the unit? Similarly, on the cold side, what is the temperature being pulled in you're trying to cool?

Air-cooled systems don't care about the humidity, only the actual air temperature.



If it performed well last year and isn't this year something changed. The airflow got clogged, the air source for either the hot or cold side got warmer (leak, vent change, etc), the load significantly changed (doubtful unless you put on an addition or opened a damper that previously wasn't being used), or there is a mechanical fault of some kind.

Do you notice it running more often, or shutting off despite not having satisfied the thermostat controlling it? Has the sound changed? Has the compressor oil been checked, or is there a sight glass or level reader of any kind? The refrigeration circuit should have service taps, and possibly has a filter of its own. I wouldn't attempt any work on the refrigeration side yourself unless you know what you're doing.

(I'm an engineer at a company that produces "chillers" - air-cooled heat exchangers, water/water heat exchangers, cooling towers, furnace pump stations, water-cooling plant systems, refrigeration systems, etc, pretty much everything non-HVAC though)

Condenser trip pan draining? Check to see where 2nd floor unit drains to the outside. Check outside units to make sure they aren’t iced up.
If you suspect the condenser drain- 5 gallon wet vac with the appropriate coupling. Unit iced up- thaws- then works again.

Couple answers.

Have had the units professionally cleaned and serviced hence knowing and seeing the coils cleaned etc.
Not sure what is going on.
Return filters are new (replaced fairly regularly)
My first step was having folks look at the “mechanics” of the system. All that checked out / was brought up to spec.

Thank you all.
Chris

quote:

My first step was having folks look at the “mechanics” of the system.

Were they HVAC techs? Were they the ones that sold you system? What did these folks tell you they thought the problem was?

By your description of the problem, I'd say you have a loose return duct in the attic, pulling in hot/humid air.

Simple way to check is to measure the temp upstairs, then measure the return duct temp for that system.
Say the house temp is 74 and the return temp is 90, you're pulling air from the attic.

Having a system run non stop and never reaching the set temperature, unless it cools off outside is another symptom.

quote:

Originally posted by SIGfourme:
Condenser trip pan draining? Check to see where 2nd floor unit drains to the outside. Check outside units to make sure they aren’t iced up.
If you suspect the condenser drain- 5 gallon wet vac with the appropriate coupling. Unit iced up- thaws- then works again.

Evaporator drain, the condenser is sitting outside.