I've got a water cooler that has a centrifugal blower inside it. The blower fails to start most of the time, but I've verified that the motor works because it starts with a slight nudge. A slight torque assist gets the fan spinning, so has the capacitor gone bad? If I nudge the blower in the wrong direction, it spins too.

I found a capacitor inside the cooler: CBB65 rated at 12uF.
Similar picture for reference

This is probably a motor start and run capacitor from what little research I've done. The capacitor doesn't seem to be bulging or deformed in any way. Is there anyway for me to verify if the capacitor has gone bad, or any other test to diagnose the problem (if it's a motor issue)?

  • 2
    \$\begingroup\$ What type of equipment do you have to test with? \$\endgroup\$ Jun 8, 2016 at 22:11
  • \$\begingroup\$ A simple multimeter without a Capacitance function. \$\endgroup\$
    – Carl
    Jun 9, 2016 at 3:11
  • 1
    \$\begingroup\$ Do you have a DC power supply? \$\endgroup\$ Jun 9, 2016 at 12:33
  • \$\begingroup\$ Not really, but I've got a couple of PC power supplies + adapters lying around. Shouldn't be a problem to get +3.3, +5, +12, +20, +35V. What do you have in mind? \$\endgroup\$
    – Carl
    Jun 9, 2016 at 16:29
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    \$\begingroup\$ If you can charge up the capacitor it should hold a charge. Any of your voltages will work and be perfectly safe (don't go too high or you may give yourself a shock). Charge it up and check the voltage after a minute or so. The voltage should not droop appreciably. If you leave a standard digital voltmeter, with an input impedance > 1 megohm attached it will slowly discharge, so make the reading and remove the leads. This won't necessarily prove the capacitor is good, but if the voltage drops quickly, it can tell you that it is bad. \$\endgroup\$ Jun 9, 2016 at 17:01

1 Answer 1


You write that the motor works fine when you help it start with a nudge. Also that you can start it in the "wrong" direction. And it does not start on its own (mostly). This is indication for a capacitor which is either dead or which has lost a lot of its capacitance.

With the limited tools you have got, there is mainly one test that you can do: Purchase a replacement capacitor and install it. If it starts the motor relyably every single time, then you can conclude that the old capacitor was the problem, and you have already fixed your water cooler (yeah).

I just had a similar problem, with the extra problem on top that shipping to West Africa often takes several weeks or even months and is costly. So I learnt on this forum that even a difference of 17% in capacitance can still start your motor.

If you are reluctant to purchase a new capacitor (I am guessing, because you are posing a question here, rather than just ordering one)(it should not be too expensive in relation to your entire cooling machine), look around your workshop and see what other capacitors you have available. Or even borrow from another working appliance. Maybe you find a 10 uF, just give it a try. I propose to not go more than 20% over the rating of the original unit, i.e. not over 14 uF.

I noticed your comment about testing with mains voltage. This is what I have observed as the "normal method of testing" here in West Africa (by craftsmen who repair motors but have no proper testing tools). It is spectacular and will indeed give you some information, if you manage to have the spark and the bang. You might need several attempts (maybe 20) as mains is of course AC. You need to very quickly disconnect after charging. And I will not give you lectures about handling mains and capacitors. But we suspect that your capacitor is dead and you cannot prove that with the spark-bang-test.

Anyway, John Birckhead has already written nice testing instructions. Testing for "not working" is harder than testing a properly working unit. So again, if you have any other capacity available, you can double-check if you have a good set-up and how a working capacitor behaves. hth


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