Central-AC suddenly not as cold

This past Saturday was brutally hot here. Temps around 96-97, heat index well over 100. We were out & when we got home around 1pm the house seemed a little warm. Not surprising given that our HVAC was never up-sized when the 2 new additions were added in the mid-90’a, and our attic insulation is minimal. However, about an hour later it felt really hot, and I discovered the inside temp was over 80, even though the thermostat was set on 73. 

I replaced the filter - it was overdue - and by the next morning the temp was down to around 76 in the house. However, by about 2pm it climbed back up to 80. The AC never stopped running the entire time, but I’m only seeing a ~5 degree temp differential between the ducts & cold-air return.

This cycle repeated until last night, when outside temps finally dropped to about 76. This morning the inside temp was 74, so I set the thermostat to 74, and it cycled off/on a few times all morning, seemingly working ok. But once outside temps got into the 80s this afternoon, the inside temp kept climbing to the upper 70’s.

What could be causing this? Freon loss?

I’m having a similar issue, can’t seem to get the output cold enough to offset higher temperatures. Let me know what you find

I am no expert but you should easily see a 20 degree differential between intake and outlet, regardless of it being undersized. My guess would be that its low on freon, but then again I am no expert. 

We've just had similar issues - the a/c for downstairs kept running the compressor continuously in hot weather. Turned out to be about 4lbs low on Freon. Unfortunately it looks like the PO had run it like that for a while and the compressor is making funny noises. New system being installed tomorrow (:/).

I'd get the system checked over to make sure it's not low on refrigerant or has other issues like the coil icing up.

Have the evaporator coils been cleaned recently?

No help, but I'm having the same basic problem.  It was into the 90s today and the A/C has been running all day and by 5pm it was up to about 84 in the house.  I've cleaned the compressor coils, put in a new filter, sealed up the unit a bit better to keep it from blowing all the cold air into the basement, and none of that seems to help.  I'm guessing low on R-410.

Thanks for the reminder to clean my coils. 

Good luck to all. 

Pete, run the fan without the ac on for a few hours. At this point your best case scenario is that the coils iced up because of the overdue filter change. If they thaw, and stay thawed after turning back on, then you’re good. If not, you’re low on freon. 

In reply to NOT A TA :

No, but thanks for the reminder!

In reply to mtn :

It’s not quite cooled down enough to try that yet, unfortunately.

We did need to have some Freon added 2 or 3 years ago. If it’s low again that would mean we have a small leak somewhere, correct?

We just had very similar situation on July 3rd, and ours was low on freon and had iced up the coils on the inside unit, preventing proper heat transfer.

If your coils are iced up, you need to to turn off the system and let it thaw for several hours before a repair tech can diagnose/recharge.

We wound up having to replace our 16 year old unit because it was leaking freon, probably at the evap coils due to corrosion.

So, good luck - hopefully yours can get a bit of freon and be back in the game.

Check your duct system.  I recall my wife's house had a duct system that consisted entirely of duct board (rigid insulation) that was taped together.  Taped.  No other means of fastening.  Ten or fifteen years after construction, the tape was letting go, resulting in huge leaks of conditioned air into the attic space. 

Not saying this is the problem in your case, but it might be worth checking out.

Pete Gossett said:

In reply to NOT A TA :

No, but thanks for the reminder!

 

In reply to mtn :

It’s not quite cooled down enough to try that yet, unfortunately.

We did need to have some Freon added 2 or 3 years ago. If it’s low again that would mean we have a small leak somewhere, correct?

It won't cool down enough, your AC isn't working. If you're worried about being comfortable, go buy a $150 window unit and throw it in for a week. Tech won't be able to diagnose it when its iced up anyways. 

I'd assume you have a leak. We do too, have to get it filled every year. I should learn how to do it myself, until we decide to replace it altogether. 

Update: he cleaned the outside unit & added a pound of Freon. It’s working well & he measured a 16-degree temperature differential which he said is good given it’s almost 30-years old. $165 well spent. 

Pete Gossett said:

Update: he cleaned the outside unit & added a pound of Freon. It’s working well & he measured a 16-degree temperature differential which he said is good given it’s almost 30-years old. $165 well spent. 

Dang it!

The day after you posted the thread, the heat pump on the kids' end of the house wasn't cooling to set point (76).  I called my guy and he verified a slightly low charge.  He put two pounds in it and charged me $297!

Found out this unit is already 10 years old.  He quoted a Dept. of Energy study that shows average life span of a heat pump is 10 to 12 years.  Probably a leak in the indoor coil, figure $2000. to replace it or just buy a whole new system, given its age.

Well, poop!

In reply to 1988RedT2 :

Ugh, that sucks!