Stumped by A/C problem

nechesgirlDecember 3, 2012


I am in HVAC Sales. I have a service customer whose system, installed by another company, cools fine until 5 or 6 pm. 2000 sf house, spray-foamed. The system is 4 ton and 2-stage cooling. It's a Comfortmaker. My Techs have been to the house several times but usually in the morning. One Tech spoke with Tech Support and filled out a report for Comfortmaker but said everything looked fine.
We suspected the 2nd stage wasn't coming on but the last Tech says it is. He didn't measure cfm but it heats fine all winter.
Has anyone out there had similar troubles with a Comfortmaker? This is the second system of that brand we haven't been able to diagnose but the neighborhood has 30 others that work well.

Any suggestions? Experience? It's a gas system, 16 SEER. About 3 years old.

I have the report in front of me if you need the readings.

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Where is this located and what are the ambient temperatures?

    Bookmark   December 3, 2012 at 4:29PM
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I missed that important detail, didn't I? East Texas. 99-104 degrees most of summer.

Brick house, horizontal system in attic, hard-pipe, no shade trees. Faces south with most windows on the east side or under covered patio on the north side.

    Bookmark   December 4, 2012 at 2:57PM
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Does the condenser sit in the sun all day? If it is 104 degrees in the shade, then it must be 130+ in the direct sun. The unit may not be able to operate under these severe conditions.

Try giving the condenser some shade and see if it performs well at 5pm.

    Bookmark   December 4, 2012 at 4:03PM
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unreal that you have to come to
online hvac forum to solve the problem.

there isn't enough info for anyone
to do more than your company has..
take a guess.

has your company any experience with foam sealed
attics? is the gas furnace self condensing or
does it have 80% furnace with combustion air
added to unit?

to me...the starting point for a/c performance
would be to see if air provided is being delivered
into the living space of the house. not leaking
into attic.
then using data loggers, set up to take hourly readings
to track how often unit is comming on
and how much humidity it removes during the
run cycle..and how much RH increases between cycles.

send the afternoon...probably next summer
unless we get some hot December afternoons.
sending tech before 2 pm to troubleshoot these
problems is just pissing away homeowners time & money.

in high summer the unit should run continuously
from mid afternoon into evening. with that 500 sq
ft per tons sizing the unit probably runs 5-15 minutes
and doesn't remove enough RH for comfort.

if equipment is correctly installed, then you
work from there to eliminate problems.

if you can't solve the problem..recommend some
one who can. call someone who can test house
& ducts and do a house diagnostic service.
keep their contact info for future use.

comfort institute, RESNET, BPI have trained
people who solve these issues if it is
beyond the abilities of your company.

best of luck

    Bookmark   December 5, 2012 at 2:22PM
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