Have older house air conditioner, need motor run capacitors. Compressor uses 370vac cap, easy to find. Blower uses 2.5mfd 440vac cap, hard to find.

Can I use 370vac caps in both locations?

If I'm unable to find 2.5mfd, would I be better off by subbing with a 2mfd or a 3mfd?

 

Responding to Larry T's 04-Jun-08 (00:27) query... See the thread at http://www.control.com/thread/1026220331 "Size of 'Run' Cap!

Regards, Phil Corso ([email protected])

 

You can use 2 capacitors in parallel to replace the 1. Capacitors in parallel add so if you could find 2 1.25mfd at 440vac that would be the same. Any combination of 440vac capacitors in parallel that add to 2.5mfd would work.

What is the supply voltage? I have a masters degree in EE so I should know this but I think as long as the voltage exceeds the supply it should be OK. In som instances though an inductance like a motor can produce an inductive kick that exceeds the source voltage so you need something with a higher voltage.

Hope this helps. I am new here and this is my first attempt to help.

 

Larry, are you sure the compressor motor's RUN cap is 370mfd, and blower's RUN cap is 2.5mfd?

The larger cap is usually an electrolytic used intermittently for START duty. The smaller cap is usually an oil-filled type used continuously for RUN duty!

Please clarify!

Regards, Phil Corso ([email protected])

 

You can get these from Graingers for $9.25

Capacitor, Universal, 2.5 mfd to 12.5 mfd
Capacitor, Universal, Control Volts 370-440, Temp Rating -40C to -70C F, For Use With 14 Different Size Motors, 2.5 mfd to 12.5 mfd

The link is: http://www.grainger.com/Grainger/wwg/productIndex.shtml

I hope this helps,
Bill

 

No, the Compressor run capacitor is 370VAC, the blower run capacitor is 2.5 mfd at 440VAC which I cannot find. Wondering if I could use a 370VAC rated cap on the blower motor, or should I not be able to find one, could I opt for a 2mfd (less phase shift, I think) or a 3mfd (more phase shift, I think), or is this value critical?

Larry

 

Larry...

1) No, you must not substitute a 370 mfd unit for the 2.5 mfd unit!

2) Yes, you can substitute a 3.0 mfd unit for the 2.5 mfd unit as long as it is oil-filled and not an electtrolytic type

3) The effect will be a slight improvement in power factor!

Regards, Phil

 

Larry, I apologize for having confused voltage with mfd!

If your question is, "Does applied voltage, if different than a capacitor's rated voltage, change the effective MFD of a capacitor?" The answer is, "Yes!"

I suggest you search List Arcvive for,

Thread # 1026195082 "Motor Run Capacitor Theory"

Regards, Phil C.