Good morning,

I have a couple of new window unit ACs, they start in eco mode. Eco mode doesn't cool the room as well as cool mode. In an online search I found that they claim ECO mode runs the compressor at a slower speed. Wouldn't that take a special kind of motor? It seems like it just turns off the fan and might play around with thermostat settings. My question is, is the compressor really running slower?

 

Good morning,

I have a couple of new window unit ACs, they start in eco mode. Eco mode doesn't cool the room as well as cool mode. In an online search I found that they claim ECO mode runs the compressor at a slower speed. Wouldn't that take a special kind of motor? It seems like it just turns off the fan and might play around with thermostat settings. My question is, is the compressor really running slower?

I can't answer your question specifically but I can say at least "it is entirely possible." I have recently done some investigation into the workings of scroll compressors, how to increase/decrease the output, and since most scroll compressors are refrigerant compressors, most of what I read was about refrigerant compressors.

There are multiple types of them, multiple strategies for variable control, and one of them is a variable speed compressor that runs either BLDC motor or induction motor with VFD to control the speed. Other methods include:
1. Motor runs at constant speed but compression is rapidly cycled on/off by disengaging the scrolls from one another.
2. Motor stops and starts frequently (I think what we are most familiar with)
3. Motor runs constantly but compression is varied by relief valves
4. Motor runs constant speed but a swashplate piston pump is used and the swashplate is flattened to receive the load.
(There are more)

 

Neither can I answer your question directly. But I want to share this with you: Last year we got AC for the home. The compressor is, as I was told, an inverter type motor - which I completely don't understand. However, according to what I was told the compressor will run depending on the cooling load. If I want to cool the house quickly to a much lower temperature it will run on - I'll call it "High". As the load diminishes the compressor begins running at lower levels. I can't say it's High, Medium and Low. From what I understand (or was told) it should be infinitely variable. I would imagine window AC units are "Probably" being built in a same fashion as it saves energy.

The best way for you to know for sure is to get a hold of the owners manual and read read read. Reading has never been my strong suit. From your description I wouldn't be surprised if your compressor DOES run slower in eco mode.

I have battery powered lawn equipment with variable settings and brushless motors. That seems to be the thing these days. Of course battery powered motors are different from AC powered motors. But I hear there's a whole lot of new technology out there. I wouldn't be surprised if your AC has an inverter motor.

 

Airconditioners these days need to have variable speed compressors in order to meet the latest efficiency regulations.
Virtually all heat pumps have variable speed compressors.

 

https://www.microchip.com/en-us/tools-resources/reference-designs/aircon-board

Air conditioner (A/C) designs need to meet stringent energy efficiency ratings and power factor specifications to reduce overall power consumption. High energy efficiency is achieved by using an inverter-based variable speed drive for the brushless motor-based compressor and condenser fans. The variable speed drive and the sensorless field-oriented control (FOC) of brushless motors allow an appliance to operate at an optimal power setting compared to a fixed-speed single-phase AC induction motor (ACIM) drive. Power factor correction (PFC) is required for all high-power appliances to connect to the electrical grid.

Microchip’s Air Conditioner reference design, based on the dual-core dsPIC33CH family of digital signal controllers, demonstrates efficient control of the condenser fan, compressor, PFC, and the overall application logic implementation. The high-performance dsPIC33C DSCs (Dual-core dsPIC33CH DSCs and Single-core dsPIC33CK DSCs) offer the right set of peripherals that is ideal for dual motor control and enables replacing three controllers with one for a cost advantage in your design.

This reference design has proven power stages for high-power PFC (220V, 1.8 KW), condenser fan (120 W), and compressor (1.34 KW) motor control. Additional features like temperature sensor interfaces, field communications, and valve drives will enable you to develop on this platform for a wide variety of air conditioner systems like window A/Cs and the outdoor unit of split A/Cs.

 

Curiosity got the better of me.

The more you know!

 

That's how you run a three-phase motor off a single-phase supply.
And speed isn't measured in Hz. The drive frequency is related to rpm of the rotor by the number of poles.

 

Consider that all of the window air-conditioners I have ever seen use sealed unit compressors, and being quite familiar with the construction of compressors, there is no chance of the compressor having a variable displacement function. That level of complexity would be much more expensive. So the only way to vary the compressor delivery rate will be to vary the compressor speed, or switch it on and off rather frequently. So it may be a variable speed brushless inverter driven (BLDC) motor, which would be my guess, unless it is cycled on and off.
If the compressor is cycled that should be obvious by listening carefully and feeling the unit's vibration.
If it is actually a variable speed motor that should be apparent by the sound, also.