How much current is drawn by an 18,600 BTU A/C compressor while running at atmospheric pressure

[HVManiac]

Hi folks,

I recently got a 26 year old hermetic A/C compressor. I plan to use this as a vacuum pump mostly for some of my hobby projects after adding an air filter and a moisture removal setup to it.

The specs on the label on the A/C said that it power draw is 2450 Watts, 11.5Amps.

Does it mean that the current draw is 11.5 Amps always or is it only while there is some load on the compressor like while it is compressing some refrigerant or gas? Also I noticed that the compressor isn't very loud while its outside compared to when it was inside the A/C it was quite loud.

Also I heard that the compressor oil gets acidic while exposed to air. Is it true? Or does the oil become acidic only when the freon is present?

Thank in advance guys.

 

[Pete999]

Hi folks,

I recently got a 26 year old hermetic A/C compressor. I plan to use this as a vacuum pump mostly for some of my hobby projects after adding an air filter and a moisture removal setup to it.

The specs on the label on the A/C said that it power draw is 2450 Watts, 11.5Amps.

Does it mean that the current draw is 11.5 Amps always or is it only while there is some load on the compressor like while it is compressing some refrigerant or gas? Also I noticed that the compressor isn't very loud while its outside compared to when it was inside the A/C it was quite loud.

Also I heard that the compressor oil gets acidic while exposed to air. Is it true? Or does the oil become acidic only when the freon is present?
View attachment 43051
Thank in advance guys.

What do you mean when you say the compressor was loud when outside compared to when it is inside

 

[HVManiac]

What do you mean when you say the compressor was loud when outside compared to when it is inside

Sorry for making it confusing. I meant that while the compressor was part of the a/c running with freon it was loud like how a 1.5 ton a/c is usually. But once I removed the compressor out of the a/c after the freon was removed and connect to the power outlet it was only as loud as a toy motor.

 

[dmxtothemax]

could be because there is no load on the motor ?

 

[telectrix]

I'd say that the rated current is 11.5A when the motor is running at it's design loading. on no load it will be less. less amps = less noise. a bit like children.

 

[Marvo]

If you're using it as a vacuum pump why do you want to fit a filter and dryer to it?

Yes refrigeration oil can be dangerously acidic but usually after a compressor has burnt out. The high temperatures during the burn out and the carbon and other contaminants produced cause the acidity. Under normal operation the oil shouldn't become acidic.

Another problem will be that the compressor oil is in direct contact with the gas being pumped through it (in this case it will be air) and air contains moisture. The oil is hygroscopic and will absorb the humidity in the air which will in turn shorten the mechanical lifespan.

Running time will also be critical, in a well designed/adjusted refridgeration system the gas entering the compressor on the suction side also contains some 'saturated vapour' which further evaporates inside the compressor and effectively provides some cooling effect. Without this additional cooling the lifespan of the valves may be reduced and you won't have this effect when pumping a 'non-condensable' gas like air. It's probably a good idea to keep the running durations short and a long off period to allow cooler operation if possible although it's a fine line because you want the oil to at least get good and warm to get rid of some of the moisture it's going to absorb.

Oil depletion will also be an issue. In a recipricating compressor (piston type) refrigeration system the oil in the compressor is constantly leaving and being carried around the refrigeration system by the refrigerant gas. Great care is taken to design the system with pipework sizes to ensure a high enough refrigerant velocity to return the oil to the compressor on the suction side. If you use this type of compressor on an open system that's not returning the oil then over time the oil will be lost and when the internal level becomes too low the compressor will seize up or burn out.

Compressor noise issues can go either way, it depends on many variables. Sometimes a compressor can become quieter as the mechanical load and internal temperatures increase, this is often a sign of excessive mechanical valve wear. Other times the noise may increase as does the mechanical load which may be bearing damage. I wouldn't read too much into the noises it makes, especially if you're running air through it, unless it starts sounding like a Russian tractor....in which case it's probably already game over.

The current stated on the info plate is the maximum running current the compressor can endure. In a refrigeration/air con system the running current varies quite considerably depending on the head pressure / ambient air temperature and how clean the condensor is etc. Usually the actual running current would be less or much less than the figure stated.