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Heating & Air Conditioning

Need help on A/C problem

15 years ago

I have a new Trane furnace and evap coil installed last year, but kept my old 3-ton 9 SEER carrier outdoor unit. Most of the time the A/C is running well, however, it sometimes loses cooling capacity after running 2 or 3 hours. When it happens, the air still blows out of the registers with the right force but it's not cool, and the compressor and fan of the outdoor unit continue running without any abnormal noise. After shutting down the system for about 30 minutes, my a/c is able to come back to the normal cooling state. I would like to call in a service tech, since I am new to this, hope someone can give me some hints about what the problem might be so I can be better armed with the right knowledge and know what to talk to them.

Thanks in advance!

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Comments (5)

ryanhughes
15 years ago
You should have matched the outdoor unit to the coil, but I can see why a contractor would do this temporarily if you plan on replacing the outdoor unit soon. You can't be sure of the capacity with a mismatched coil, so that may very well be what's happening. However, I would think that you would notice it during the whole cycle, not just at the end. Something doesn't sound right, so you should have a tech out. Ask him to check airflow, dry and wet bulbs, superheat (or sub-cooling if you have a TXV), TXV, etc... A good tech will know what to look at.
zl700
15 years ago
Moisture in system could plug the new coils TXV over time, causing the gas to bypass until it is shut down and melts.

Was a proper evacuation done and a filter dryer installed?
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jefftrane
Original Author
15 years ago
Thanks for the quick replies. I don't have TXV installed. In regards to the installation, I don't know the details, I simply trust them as I found the company from Trane web site, they are Trane authorized dealer in my area. I can confirm my coil is 5 ton, as I questioned them if the 5-ton coil can match my 3-ton unit, they told me the 5-ton coil can improve the efficiency of my 3-ton unit, it should work well. I am not supposed to replace my 3-ton unit as it's only 5-year old and works as expected with my old system. Can I still trust the company ? or find a tech from another company?
joeplumb
15 years ago
The fact that he has good airflow and warmer output rules out blockage or ice formation.
I would look for a problem at the fan of the outdoor unit. Check that the condenser fan is running and warm air is flowing out of it when unit acts up.
zl700
15 years ago
No TXV and a 5 ton coil on a 3 ton condenser??

How would a tech know what orifice to use/replace within the distributor of the cap tube expansion device?

Most likely they left the oversized 5t orifice in the coil and it is passing too much gas, thus no sub-cooling.

The operation pressures and superheat would confirm this.

Note, I didn't mean icing exterior of coil

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