The Hotline: 05/02/2005

April 28, 2005
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Condenser Coil

QUESTION:
From Hugh Gither
Pensacola, Fla.

Prior to changeout, a condo had a 1.5-ton condenser and a 1.5-ton air handler (evaporator coil). The condenser coil was 23 years old. The seller agreed to change out the condenser unit. Upon inspection of this new unit, a local A/C company changed the 1.5-ton condenser out with a 2-ton unit. Currently we have a 2-ton outside unit with a 1.5-ton unit inside. Is this a problem, and, if so, why?

ANSWER:
By Daniel Kramer, P.E.
Specialist Grade Member of RSES

No, I really don't think you have a problem. In fact, in discussions of mold buildup and excess humidity, recent articles have been suggesting that the airflow rate over the cooling coil should be reduced (the equivalent of increasing the compressor size relative to the evaporator) to lower the suction pressure to get a better dehumidification effect. In Pensacola, I'm sure the humidity is frequently high and better dehumidification would be a plus.

The only concern you might have is that the evaporating temperature in the evaporator may fall below 30 degrees or 32 degrees F. You can check this on an 80 degrees or warmer day with the system fully charged by observing the evaporator pressure and making sure it doesn't fall below any of the following pressures. For R-22, the pressure corresponding to 30 degrees is 55 psig. For R-410A, it is about 97 psig. For R-134a, it is about 26 psig.

If the evaporator pressure does stay below these limits, you should suspect a dirty evaporator coil. Inspect and clean it. Also, if necessary, increase the fan speed. In a worst case, you might have to throttle the suction service valve a little to cause the evaporator pressure to rise.

Blower Motor

QUESTION:
From Richard Hawkins
Mansfield, Ohio

I had a flood in my basement. I had it cleaned up but now my blower motor is not working. It does put out heat, but not enough. The furnace turns on but also shuts off after a minute or two. It puts out heat upstairs but not downstairs. What is causing this?

ANSWER:
By Dave Anderlik
Consultant

It is not unusual for a furnace blower motor to fail due to a flooding. With a failed blower motor, you are seeing your furnace cycling on the high limit control. The control is designed to protect your furnace from damage caused by overheating and to protect your property.

Your furnace blower motor needs to be replaced as soon as possible and the furnace should not be used until it is replaced. The reason you are getting some heat upstairs is because hot air is less dense (lighter), which causes it to rise.

Solid State

QUESTION:
From John West
Chesterfield, Va.

My question involves GE Motors model number 5SME39SL0601 ECM programmable motor. What would be the best way to determine if the solid-state area is defective or the motor? Why do you have to purchase the whole piece if the solid state is OK?

ANSWER:
By Paul Goldman
Business Leader
GE ECM
Fort Wayne, Ind.

The best and simplest way to determine if the problem is with the ECM or in another part of the HVAC system is to use the TECMate or other troubleshooting device that powers the ECM independent of the HVAC system.

The TECMate connects directly to the ECM 16-pin low-voltage control connector. The five-pin power connector remains connected to the AC power. There are two leads on the TECMate that are then connected to the 24-V source within the furnace or air handler.

If the TECMate operates the motor, then the issue lies somewhere else in the HVAC system. If the TECMate does not operate the ECM, then you need to determine if just the motor control module is damaged or both the control and the motor. (Caution: Allow five minutes after the removal of the AC power before attempting any disassembly of the motor/control.)

To determine the extent of damage, remove the two hex bolts that attach the control to the motor. Once open, reach in and unclip the three-pin connector. Using an ohmmeter, check the resistance of each motor lead to ground (the unpainted end shield of the motor). A good motor will reach >100K ohm. This is important, as replacing the control on a faulty motor will cause the new control to fail.

In regards to having to purchase a whole piece if the solid state is OK, most of the OEMs offer the control module as a separate re-placement part. Ask your wholesaler if they carry the control module. Be sure to use the correct module, as each is specifically programmed for each application.

To learn more about the TECMate troubleshooting tool and to get a free copy of "Home Comfort Guide" that has all the steps to proper installation and service of ECM systems, log on to www.geindustrial.com/dealer.

If you have a technical question, fax it to 847-622-7266 or submit it online by visiting The News' Extra Edition page and clicking on The Hotline link in the left-hand column.

Publication date: 05/02/2005

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