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Old 04-22-16, 01:15 AM   #1
gtojohn
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Default Retrofitting condensing units with hi efficiency ecm

The outdoor fan motor on my 15 seer trane/american standard condensing unit went out yesterday. I found out today that even though its only 7yrs old its out of warranty. It was equipped with a ecm motor for a whopping $480 i could get the oem replacement. Specs show 825 rpm 1/3 hp. Part of the 15 seer is gained from the ecm motor. A quick check of rescue motors and options and I've found the mars azure 10874 ecm replacement for $130 locally. I went ahead and bought 2. It was a quick and easy swap out. Paraphrasing the pamplet " measuring amps won't be a good indicator of efficiency because of its low power factor." Fan amps were .6 at 246vac with total condensor amps at 6.0 for 2 tons. Unfortunately i don't have before amps for this unit but I suspect close to the same. Next retrofit my older 2006 ruud 14 seer 2 ton unit. Originally a 850 rpm 1/10 hp psc motor. Motor amps .6 and condensing unit total amps 7.4 amps. 15 minutes later and new motor is in place. New motor amps .6 but total unit amps at 6.7amps. I'm not totally sure why. Is it the low power factor or is the additional hp is condensing more and reducing head pressure for the same .6 amps as before. More importantly is the savings of .7 amps at 240v for a savings of 168 watts.

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Old 04-22-16, 01:40 AM   #2
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Old 04-22-16, 08:18 AM   #3
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Your pic wouldn't show, so I uploaded it directly. Here it is:

Yep, the new motor is not slowing down, forcing a lower condensing temperature. In my limited experience, I have found that with cap tube driven systems, you lose a little capacity at lower outdoor temperatures. Your trade is lower compressor power draw. Also, the indoor unit may try to freeze up.

With a txv driven unit, most of these problems go away.
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Old 04-24-16, 05:20 PM   #4
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You lose capacity? I specifically ran my air conditioner [non-TXV, uses a piston orifice] when it was at the coldest point of the night as long as it was 60 degrees or warmer and it would always condense more. ..which I equated with a colder evaporator which would mean higher latent capacity and I'd figure higher total capacity. There were a few nights where it was colder than the forecast and it got to 55 degrees and it froze the coil and the lineset back to the condensor. ..whoops, but the recip compressor survived. I should rig in a low ambient kit or at least a sensor that shuts things down if the liquid line gets below 40 degrees or so. The bonus is also the reduced power draw with a colder condensing coil. I thought these were good things as long as the evaporator coil doesn't freeze up and/or liquid refrigerant returns to the compressor.

I'd figure if you've got higher flow over the condenser coils, it is effectively like having a larger coil. Larger coils are a part of higher SEER systems because they use less energy to perform the same or more heat exchange. If there is a higher flow AND the system is using less energy, I'm seeing this as a win-win.
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Old 04-24-16, 07:26 PM   #5
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Yes, with your flow rater (constant pressure expansion valve or CPEV) metered system, you will not get the reduction in capacity as with a cap tube. For low-ambient operation, what you would want to do is put a high-pressure sensor in on the fan circuit so the fan doesn't start until the condenser reaches a certain pressure. Or you could rig a defrost sensor onto the suction line that would cut the compressor when the evaporator coil froze. Either way would yield reliable operation.
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Old 06-12-16, 08:57 AM   #6
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Compressor amps are VERY sensitive to head pressure. Outdoor temp and total CFM are the major players, provided system charge or indoor airflow haven’t been messed with. Was the outdoor temp about the same for both tests? IMHO an ECM condenser fan motor doesn't make sense when used with a single stage compressor. At $136, it's not much more than a standard PSC motor so payback might be decent.

15SEER should be a TXV, the TXV will adjust to keep a constant superheat and be efficient under most operating conditions. Lower head pressures will typically result in a colder evap coil.
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Old 06-12-16, 05:14 PM   #7
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Could you power factor correct the motors??
Those small fractional horse power motors are usually by far the least efficient.

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