We turned our a/c on yesterday for the first time this season. It was about 85' outside, the thermostat (as it's always been) was set to 75', but the interior of the house never got below 76' and in fact climbed up to 82' as the day went on. So obviously something was wrong.

I checked that the system seemed to be working okay, didn't see any frost or signs of freezing up, no apparent leaks, the hardware outside was working fine, and so on: it just wasn't cooling the air as much as it should've been.

When I checked the filter, it wasn't horribly gunky but was definitely more grey than pristine white. It was last replaced in late January and hadn't been touched since then, so about three months old. I swapped it out for a new this morning today and now a/c seems to be running stable at 75'.

I'll be the first to admit I don't always remember to replace the filter every month (or two or three) but having almost ten degrees' difference between the old and new filters seems surprising. Can that really have such a drastic effect on temperature control?

Thanks!

 

Yes it can have big effect on cooling. What kind of filter are you using, 1"?

 

I don't have it in front of me, but I believe it's 20x25x1.

 

Just wanted to make sure it wasn't the 4" filter. They can reduce your airflow.

 

That's another reason I thought this was weird: this is definitely not the first time the filter has sat in there for a few months (and it's always been 1") but it's the first time I've noticed such a lowered airflow/cooling. The only difference I'm aware of this time was that the maintenance guy put a new filter in himself in January; maybe it just wasn't as good quality as I usually use and so blocked more air.

 

It would appear that the filter was for some reason reducing the airflow too much. Was it a 1" deep pleated filter?

Many valid performance tests have shown that air conditioning systems 'on the average' only deliver to the conditioned areas between 59 & 63% of their Nominal Rated Performance.

Easy Safe testing of your A/C or heat pump cooling performance for all the visitors to use; if your unit does not come within a few degrees of these test figures, call an HVAC service contractor:

First, make sure the return air filter is clean, and then you should get a digital probe thermometer that reads in tenths degrees, (though U can use any mercury thermometer) and a low cost percent relative humidity gauge to check the 'indoor' humidity level.

If you have an air conditioner that was manufactured between 1992 and 2005 it will 'probably be' a 10 to 12 SEER R-22 refrigerant unit.

When the temperature reaches around + 80 to 95°F outdoors and the indoor temperature is 80°F and the relative humidity indoors' is right around 50% RH the outdoor condenser temperature split should be around 20 to 21°F above the outdoor temperature.

If the indoor temperature is 75° and the relative humidity is 50% then the air discharge temp-split off the condenser should be around 17°F.

The indoor temperature split between the return-air at the supply air grille closest to the air handler should be a 19 to 21°F temperature drop with either an 80°F or 75°F indoor temperature. This is also the indoor split with the higher SEER units at 13 SEER or above.

If the indoor temperature split is too high may have very low airflow which needs to be brought up to its normal CFM Rate.

If the outdoor condenser split is too high your air handler may be drawing hot air into the return from the attic causing the high condenser discharge air temperature.

On the new air-conditioning systems & any systems at 13 SEER or higher, the outdoor condenser split is much lower than it is on the 10 to 12 SEER units; the indoor temp-split is the same.

If the temps are within plus or minus a degree or two, that air-conditioner is performing fairly well; if not call an HVAC service contractor.

 

I bet it isn't the filter.