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Old 07-21-22, 12:45 PM   #1
Lurking Renovator
Join Date: Jul 2013
Location: central MS
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Default air conditioner advice needed


I need to mine the HVAC brain trust here about my home A/C; hoping it's not inappropriate to ask here.

My Trane central units are around 25 years old. They were pretty high efficiency for the time of mfgr, and have required minimal maintenance considering their 25 year age (a couple of capacitors and the air flow motor in the compressor, control boards in the air handlers at different times, and one pressure sensor for the heater section).

This summer, the primary unit *seems* to be under-performing, but because conditions have changed in the house, I'm uncertain whether to blame the A/C or the changing conditions.

We normally close off about 40% of the house, and only run the primary unit. Last year, we opened up one of the bedrooms & a bath that had been in the '40% zone', but just let ambient air from the main part of the house cool it. The HVAC vents in the room are plugged.

This summer, when it became obvious that there were performance issues, I started investigating. Both the evaporator coil and the condenser coils were quite dirty; they've been cleaned.

I've checked return air/register air using a cheap indoor/outdoor thermometer. Before cleaning, temp delta after a short check was ~11-12 degrees F. After cleaning, and letting the system run for quite a while, delta finally got to ~18 degrees F. Right now, it's 17 degrees. It seems to take a long time (several minutes minimum) for the delta to get that wide. Not sure whether that's an A/C issue, or slow response of the cheap thermometer.

It's very humid in MS, and I've had problems with moisture condensing and dripping as air leaves the registers near the air handler both before and after cleaning the coils. The condensate drain is clear (verified when I cleaned the coils). The air handler is under the house; the vents blowing water are near the ceiling. They're a good 10' above the evaporator coil.

A couple of very curious details; at least to me: When I cleaned the evaporator coils (typical A frame shape, laid on its side in the air handler), I found a piece of sheet metal covering over half of the top side of the 'A', and wedged into the metal flange at the apex of the 'A'. The other odd seeming thing is that when I started to clean the evaporator, I got interrupted, and didn't get back to cleaning it for about 1 1/2 hours. When I got back to cleaning, the coil itself, pulled about half way out of the housing before I was interrupted, was *still* cold and condensing moisture out of the air.

We normally turn up the thermostat to ~75-76 in the daytime, and down to ~69-70 at night. It's taking a couple of hours to bring temps down from 75 to 70. This seems to be excessive, with daytime outside temps in the mid/high 90s and evening temps in the mid 80s. Mitigating that is the fact that we added about 250 sq ft to the previous ~1400 sq feet that the unit was handling.

I have not done any refrigerant pressure measurements; that's a skillset & tool set I have not yet acquired. Sorry for the long post, but I was trying to include as many details as I could.

Thoughts from those experienced with refrigeration systems and HVAC?

I can find the money to replace the system, but I don't want to needlessly replace it if it's simply a situation where we're getting near the system's capacity.



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Old 08-04-22, 12:34 PM   #2
This Old Geek
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I had a valve problem year back that had the exact same issues ... basically letting more by then it is suppose is what I was told. then can only be verified with testing the pressure while at rest and then running. Thing is he told me it may have just needed Freon but he checked everything and said the valve needed replaced and adding it at this point might mask the fact till it quits altogether (the valve). We replaced the unit do to efficiency. The old unit would need all Freon removed. Then replace the valve. Vacuum the system and lines. Then replace the Freon. At the cost of labor and Freon We decided to go to a more efficient unit. I hope that all makes sense. Short version get lines tested to see what the issue is.
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rvCharlie (08-04-22)
Old 08-04-22, 03:12 PM   #3
Lurking Renovator
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Thanks for the info; what you're describing is the one thing I've heard from other sources as a possible cause.

Since sending the original message, I paid a guy come out to check both my systems. Recommended by a friend, but he's a solo act & I've never dealt with him before. He put his gauges on it (while running, only), and said there was nothing wrong even though I told him it takes a long time to get to even 17-18 degrees of temp spread. He blamed the high outdoor heat & the extreme humidity here in MS. I did ask him whether there could be any issues other than freon levels, like valving, etc, but he shrugged that off without any further checks.

We've now closed off that extra bedroom/bath area, and the system is doing significantly better, but I'm still getting 'high humidity' notices from the smart thermostat after taking a shower, etc (new development), and it still takes a couple of hours to drop 4 or 5 degrees in the house.

I guess I'll see how our KWH number looks for August compared to last year. July was significantly higher, but that extra sq footage was open then. I'm still kinda expecting to have a new HVAC bill in my future....

Anyone have any thoughts on inverter style systems in rural areas with really unreliable electrical utilities? Our power seems to go off when it rains anywhere in the county, and some of my electronic stuff complains when running on my old Generac automatic backup generator. The AC tech that came out wasn't a fan; said they're not ready for prime time in areas like mine.

Thanks for any thoughts,

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