Simple Test to Check Outboard Condensers with an Analog Multimeter


Note: This is a synopsis of Frank Robb’s post on the AOMCI website.

    First, remove condenser from the motor. So as not to discharge the condenser, handle it with one hand and set it on a non-conducting surface like wood, cardboard or paper before testing.

    Set the resistance (ohm or Ω) scale on the multimeter to a medium scale, like X10k. Touch the two meter leads together and adjust the meter to read zero on the resistance scale.

    Touch the meter leads to the condenser case (negative lead) and wire terminal (positive lead).  You should see the meter deflect quickly toward zero (discharge), and then slowly returns toward infinity as the battery in the tester recharges the condenser.  It probably won't go all the way to infinity.  The reading it goes to represents the condenser leakage. A higher resistance value (smaller deflection from infinity) is better.  Touch the wire to the condenser case to discharge it before repeating the test.

    If there is no initial deflection toward zero on the test, then the condenser is “open”. 

If initial deflection toward zero and returns to close to infinity

Condenser is not shorted and taking a charge

If initial defection toward zero and a large deflection from infinity

Condenser has partial short

If no initial defection toward zero

Condenser is open

    If there is too much leakage (a large deflection from infinity on the scale) then there is a partial short in the condenser. 

    Sorry, there is no way to read exact capacity (mfd or µF value) of the condenser with this test.   In general, the speed at which the meter returns toward infinity is an indicator of condenser capacity (compare with a known good one).  Slow return to infinity indicates a greater capacity of the condenser (higher mfd value) that a fast return (lower mfd).  You are also testing it at only 1.5 volts, less than in actual operation.  But it is a good quickie and cheap test.

FAST deflection toward infinity on scale

LOW mfd capacity to condenser

SLOW deflection toward infinity on scale

HIGH mfd capacity to condenser

    There are other factors involved with the speed of the deflection.  The deflection time can be affected by variables such as the range setting on your meter and the amount of “leakage” of the condenser.

    This kind of test is useful, but only a crude test.  Generally speaking, if it passes at all, it probably will work in a motor.  Unless the deflection time toward zero is VERY DIFFERENT from a known good condenser, the capacity is way off and probably should not be used.