Variable Speed ECM Condenser Fan Motors | HVAC Refrigeration


Variable Speed ECM Condenser Fan Motors - High SEER Trane Condenser Variable Speed ECM Condenser Fan Motor

This high SEER Trane condenser uses an ECM variable speed fan motor to modulate the speed of the fan

Variable Speed ECM Condenser Fan Motors are used in condensers for the high efficient models so that the fan speed for the condenser can be modulated according to the load of the system. The ECM fan motors are used in condensers that either have a modulating compressor or condensers that have two compressors where one compressor is small and one compressor is large. The ECM motor adds to the efficiency of the system by modulating the condenser fan motor to match the compressor use needed to satisfy the load.

Variable Speed ECM Condenser Fan Motors – Peak Operation

On very hot days you need more air conditioning capacity to satisfy the heating load demand put on your home in the summer. In milder weather you do not need to run the air conditioner at 100% to satisfy the higher demand. HVAC equipment manufacturers have introduced systems that have the ability to run in two-stages so that on the hotter days you can satisfy the demand and on the cooler days you can run the system at a lower setting thereby using less energy.

Using less energy is the objective so how do we do this? The solution is two-fold for having an efficient running system. One is to reduce the heat gain by insulating the home and adding things to the home such as attic fans. These things help reduce heat gain to the living areas that you want to condition with cool less humid air. The second thing you can do is to purchase a higher efficient system that can modulate or offers staging from a high level for higher demand to lower level for lower demand.

Variable Speed ECM Condenser Fan Motors – The Future

HVAC Manufacturers introduced two-stage compressors and in the future (offered currently in commercial systems) modulating compressors that will run according to the demand based on exactly what you need to condition your space. Since the compressor would stage based on demand they needed a condenser fan motor that would also stage based on demand. Some manufacturers use a standard multi-speed fan motor while others use a ECM fan motor to facilitate a higher speed for the increased demand when the system is calling for higher demand and a lower speed when the system is calling for a lower demand. So when the compressor is running at a higher speed the condenser fan motor will also run at a high speed and when the compressor is running at a lower speed the fan motor will run at a lower speed.

High Performance HVAC

Variable Speed ECM Condenser Fan Motors


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  1. What about damage to psc motors? Are the motors specifically designed to rotate at various voltages in order to avoid burned windings? When I worked for a Carrier dealer we had an add on modulator control we would add for places that needed cooling in winter months such as tanning salons, etc. Are those still available? The reason I ask is that where I currently live we experience a wide temp swing day to night and often times cooling becomes problematic with frost-back overnight. I can’t count the times I’ve had to thaw the evap coil in the am when this happened. Are there aftermarket devices made that can safely be added to my system?

    1. What about damage to psc motors? Are the motors specifically designed to rotate at various voltages in order to avoid burned windings? No, PSC motors are designed to run at a set voltage with a tolerance of (typically) plus or minus 10%. I have seen the problem you are experiencing and my fix for the customer was to add a temperature switch on the evaporator coil. Like a freeze stat. I positioned the temperature probe on the evaporator coil and set it for 34 degrees. When the evaporator coil got down to 34 degrees a switch would open and kill the condenser. The blower keeps running until the temperature rises to a certain temperature where I set the switch to close and turn the condenser back on at 50 degrees or so. I also added a timer switch to the circuit to prevent short cycling of the condenser in case of temperature swings within a five minute period. The customer never had a problem again with the system freezing up. Depending on your system you really need a good HVAC technician who knows what he is doing to modify your system as I describe here.

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