Diagnosing the Safety Circuit Using a Voltmeter

The safety circuit can be diagnosed by using a voltmeter to determine which component(s) is keeping the safety circuit from closing. Below will guide you in checking the following components, if equipped: Fan protectors, high limits, linear limits, high gas pressure switches, and plenum door switches.

Fan Protectors

The Safety Circuit can also be diagnosed by using a DC voltmeter and the dryer schematic. Using the schematic as a guide, use the voltmeter to look for 24 vdc at terminals in the Low Voltage Cabinet. Be sure the Voltmeter is first set to read DC Voltage which is depicted with a straight line next to the V as opposed to a wavy line which depicts AC voltage. Take the black lead of the Voltmeter and place it in Terminal 320 (TB320). Next, move the red lead of the voltmeter to the first terminal of the Safety Circuit (TB341), followed in order by TB401 as shown below until 24 Volts no longer appears and 0 Volts measures on the Voltmeter instead.

• TB341 Beginning of the safety circuit after circuit breaker #341

• TB401 Fan protector #1

• TB402 Fan protector #2 (if equipped)

• TB403 Fan protector #3 (if equipped)

• TB404 Fan protector #4 (if equipped)

• TB405 Fan protector #5 (if equipped)

• TB406 Fan protector #6 (if equipped)

• TB407 Fan protector #7 (if equipped)

• TB408Fan protector #8 (if equipped)

The dryer will only have the number of fan protector terminals as the dryer has fans

High Limits

• TB421 High limit #1

• TB422 High limit #2 (if equipped)

• TB423 High limit #3 (if equipped)

• TB424 High limit #4 (if equipped)

• TB425 High limit #5 (if equipped)

• TB426 High limit #6 (if equipped)

• TB427 High limit #7 (if equipped)

• TB428 High limit #8 (if equipped)

The dryer will only have the number of high limits as the dryer has burners.

Linear Limits

• TB431 Linear Limit #1 (if equipped)

• TB432 Linear Limit #2 (if equipped)

• TB433 Linear Limit #3 (if equipped)

• TB434 Linear Limit #4 (if equipped)

• TB435 Linear Limit #5 (if equipped)

• TB436 Linear Limit #6 (if equipped)

High Gas Pressure Switches

If the dryer is an export model dryer, the following items will be included in the Safety Circuit.

• TB451 High gas pressure switch #1

• TB452 High gas pressure switch #2

• TB453 High gas pressure switch #3

• TB454 High gas pressure switch #4

• TB455 High gas pressure switch #5

• TB456 High gas pressure switch #6

• TB457 High gas pressure switch #7

• TB458 High gas pressure switch #8

The dryer will only have the number of high gas pressure switches as they dryer has burners. If there is 24 vdc at terminal #460, the safety circuit is complete.

Although the following items are not in series with the previously mentioned items, tripping any of these items will disengage the safety circuit and produce a red warning screen.

Plenum Door Switches

If the dryer is an export model, the following items, if tripped will disengage the safety circuit.

• TB491 Plenum door #1 safety switch

• TB492 Plenum door #2 safety switch

• TB493 Plenum door #3 safety switch

• TB494 Plenum door #4 safety switch

• TB495 Plenum door #5 safety switch

• TB496 Plenum door #6 safety switch

• TB497 Plenum door #7 safety switch

• TB498 Plenum door #8 safety switch