(ET) Card#3, varistor

I have a "Home Owner's service manual" which on page 1-34 has a diagram of card #3 showing a varistor across the F1- F2 terminals (field?) of the motor - I believe between positions 1 and 7 of card #3 if I read the diagram correctly. A description of the card's function (for the E-15) is "Last four speeds - by adding current limiters in motor field - R4,R5,R6, and R7 on Card #3." and "The E-15 has the same items as E-12S plus a field weakening relay, card No. 3 and corresponding switches." The schematic for the E-15 electrical system (Fig. 5-7) simply shows a "VR-1" on card 3, with no value, nor does the text mention a value.

On page 1-33 there is a diagram of card #3 with the note "varistor - energy absorbing device to prevent pick up of PTO and other devices through inadvertent triggering of SCR's from field produced voltage surge."

Other bigger models described in this manual also have a "VDR-1" circuit acoss the field terminals, which apparently comprise diodes and a varistor. No values are given, nor does the varistor show up on troubleshooting logic flow diagrams.