Alto-Shaam QC-40 User Manual download pdf (Page 7)

There are 16 LED’s on the relay board (Figure 12) that illuminate when that function of the board is

energized and can be used in diagnostics.

NOTE: THE ONLY REPLACEMENT PARTS ON THE RELAY BOARD ARE THE FUSES AND THE DEFROST

HEATER RELAYS.

When the unit is powered up, the door is closed, and the Main Menu screen appears on the control display,

the following LED’s must be illuminated: WDI, +5V, +14V,CPU.

TROUBLE SHOOTING THE RELAY BOARD

If the relay board is suspected as the problem, check to make certain the power LED, located in the lower

right corner, is illuminated. If it is not illuminated, check at the power input connector (J18) for 24VAC across

the 2 outside terminals. If there is 24VAC present and the power LED is not illuminated, the relay board is

defective and must be replaced. If there is no

voltage present, check to make certain the

circuit breaker switch is good and it is turned

ON. If the breaker switch is good, check

power by locating the terminal block in the

upper, right side of the relay board enclosure

and check for line voltage across the two

outside terminals. If the voltage is present,

then the transformer is defective and must be

replaced.

The evaporator fans are powered by the

relay board, through the J1 and J2 plugs on

the upper left corner of the relay board

(

Figure 13). L

is continuously supplied to

the evaporator fan motors and L

is switched

by solid state relays, with protection by the

2A fuses (F1-F6). L

goes to the fan

terminator located on the evaporator suction

line, which closes at 30 degrees F (-1 degree C)

and opens at 60 degrees F (16 degrees C).

CPU BOARD POWER LED (J17)

14VDC RELAY VOLTAGE LED

(REL3, REL4, REL5)

5VDC CPU BOARD POWER LED (J16)

CPU IS POWERED & CONNECTED BUT

NOT RUNNING A PROGRAM

CPU DIAGNOSTIC SOFTWARE LED

DOOR OPEN/CLOSED LED

CPU IS CONNECTED, POWERED, &

RUNNING A PROGRAM

BUZZER ON/OFF LED

FAN RELAY LED'S

DEFROST HEATER

RELAY LED'S

REFRIGERANT

SOLENOID RELAY

LED'S

COMPRESSOR

RELAY LED

2A FAN

FUSES

SOLID

STATE

FAN

RELAYS

Figure 12

Figure 13

1 2 3 4 5 6 7 8 9 10 11 12 ... 19 20

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Alto-Shaam QC-40 User Manual Page 7

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