'55 Ford car ignition condenser, 6-cyl or V8
.21 - .25 microfarads; minimum leakage 10 megohms; maximum series resistance 1 ohm; for use with standard 6 volt ignition coil, 1.5 ohms resistance.
HOW TO TEST A CONDENSER
1.) Remove the condenser from the engine (or at least disconnect the lead wire). Note the small metal connector located on the end of the condenser. This connector is the "hot" or power connection. The metal case of the condenser is the grounding point. Discharge the condenser by shorting the lead wire to the case.
2.) Switch the meter to the ohms position. Place the red lead into the "ohm" connector on the meter. Insert the black lead into the "com" or common connector on the meter. Set the resistance range to the highest available setting (if it is selectable). Connect the test leads together and zero the meter. If the meter won't zero replace the battery. (Yes, an ohm meter has a battery).
3.) Touch the red lead to the hot connector on the condenser. Place the black lead to the metal case on the condenser. The meter's needle should jump slightly to the right (toward 0-ohms), then should drop back to the left towards infinite resistance). Hold the leads in place for 15 to 20 seconds. This action places charge in the condenser. If the test shows any reading other than infinity, the condenser is leaking and needs to be replaced.
4.) Remove the leads and reverse the placement to the condenser. Move the red lead from the hot connector to the metal case and move the black lead from the metal case to the hot connector. At the moment where both leads are touching the correct points, the meter should jump towards the right. The second time the needle may move twice as far, as this action discharges the condenser. Holding the leads in contact should again result in movement of the needle back toward infinite resistance.
5.) Movement of the meter's needle indicates the condenser is good. If no movement was indicated on the meter in any circumstance, the condenser is bad and must be replaced. Retest the condenser several times for a consistent reading.
In operation the condenser will "ring" at up to 300 volts, so the condenser needs to be rated much higher, no less than 600 volts DC. The ignition will likely work with any capacitance value between 0.05 and 0.6 microfarad. Too high or too low value may eventually transfer metal from one side of the contact points to the other side leaving a pit and a point. Capacity of spark coil capacitors ranges from 0.2 microfarad to 0.33 microfarad. Almost all automotive coils use a 0.25-0.29 microfarad capacitor.
A capacitor may absorb moisture over a long period of time, and moisture can cause failure of the condenser. So it is possible that a condenser stored for 10 years or so might be bad or might fail prematurely in service. It is a good idea to check your traveling spare condenser occasionally.
HOW IT WORKS
Current flows through the points when they close. When they open the inductance of the ignition coil tries to maintain that current so an arc will be struck between them until the points open up enough to break the circuit. The more current you run through the points, the harder it is for them to break the current.
That is why point systems have a condenser (called a capacitor in any other electrical system). The condenser slows down the reaction time of the coil to allow the points time to open and break the circuit. Without a condenser you will likely never break the primary current and get no spark from the secondary. Having a condenser that is too large will completely prevent arcing across the points but will also slow the coil so much that it is unable to strike an arc on the secondary. The trick is to find a condenser that gives a happy medium between the arc at the points and the arc at the spark plug. A smaller condenser means more power from the coil but shorter point life due to pitting. A larger condenser will give you longer point life but sacrifice coil output.
