Never use an ohm meter to test a motor run capacitor. It is a very inconclusive test and only shows that there is "something" in the circuit. You are essentially "shooting blind".
The test consists of connecting the capacitor under test in series with a 100 watt light bulb on a 120 volt ac line. If you have a single pole contactor then you can test your run capacitors in the unit without removing them and use the case of the unit as ground. A two pole contactor system may not work unless one of the line leads is hot to the compressor at all times (in the highly unlikely event that you are running a single phase unit on a 240 (not 208) volt 3 phase system usually found in a commercial setting, this test will not work)! Contact me for more information. Check the circuit by connecting the light bulb from one side of the line to the case to make sure the bulb and circuit is good before proceeding! If the voltage result is for a smaller capacitor than the one under test then it is bad. I used a pigtail socket like the ones used in new construction for temporary lighting. Clip leads are available from Radio Shack. I will add some images when I get a moment.
I used a 130 volt ac 100 watt rough service bulb because that is what I had on hand and a rough service bulb is less likely to break over an ordinary 100 watt bulb. Results will be slightly different if using and ordinary 100 watt light bulb especially at the higher values.
To the results: Click here to get the chart by itself.
|Micro Farad of run capacitor.||Voltage across bulb.|
|5 mfd.||6-7 volts ac.|
|7.5 mfd.||20 volts ac.|
|10 mfd.||27 volts ac.|
|15 mfd.||70 volts ac.|
|17.5 mfd||77 volts ac.|
|20 mfd.||88 volts ac.|
|25 mfd.||98 volts ac.|
|30 mfd.||104 volts ac.|
|35 mfd.||109 volts ac.|
|40 mfd.||112 volts ac.|
C in MFDs= (2654I)/E
C in MFDs= (2654A)/V
C in MFDs= (2654 * Amps)/voltage.
C in MFDs= 2654 multiplied by Amps through the capacitior then divided by Volts across the capacitor
The 2654 is the number you get when you multiply 60 HZ by 2 PI and divide into 1 Million (6 places).
XC(Cap reactance in ohms)=1/(2PI*F)*(C in Farads) XC=Volts/Amps (C in Farads)=1/(2PI*F*I/E)
to White Rodgers that has a good look up table of different manufacturers.
You will notice that Lennox's color codes are TOTALLY WEIRD to put it gently.
Link to White Rodgers Clip art that has pictures of their different control products.
I would highly suggest identifying each wire by connecting the hot lead to each function wire with clip leads and a 3 amp fuse and recording the function before installing your new thermostat. While this is more trouble it may save you from ruining your day.
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