Chapter 1: How Does It Work; Heating System - Full Vat; Heating System - Split Vat - Pitco frialator MG14S-C/MFD Serviceanleitung

Chapter 1: HOW DOES IT WORK?

The McDonald's Gas fryer will have certain reactions to
what is happening, knowing what these reactions are
and knowing what the machine is trying to do will enable
us to diagnose most of the problems likely to be en-
countered.

Heating System - Full Vat:

• Power to the machine is turned ON:
• The computer is supplied with 24 VAC and, if the
Drain Valve Handle is closed, the Proximity Switch
will supply 24 VAC to the DVI (Drain Valve Inter-
lock) Input at the computer. The Ignition Control
Modules are also supplied with 24 VAC at the 24V
terminal.
• The computer is turned ON -
• Computer calls for heat and supplies 24 VDC to
the Heat Demand Relay which will energize supply-
ing the Blower, the Pilot Solenoid on the Gas Valve
and the Pressure Switch with Power.
• The Pressure Switch will energize the Check Blower
Relay which will stay energized.
• When the Blower reaches its normal speed it will
cause the pressure switch to close supplying 24 VAC
to the second set of switch points on the Check
Blower Relay. Because the Check Blower Relay is
still energized the power will be supplied to the TH
terminal of each Ignition Control Module.
• Both Ignition Control Modules supply power to the
Spark Ignitors. At the same time one of the Ignition
Control Modules supplies power to the Main Valve
Relay coil. The other Ignition Control Module sup-
plies power to the switch points of the Main Valve
Relay.
• The Main Valve Relay energizes allowing the sec-
ond Ignition Control Module to supply power to the
Main Solenoid of the Gas Valve.
• At this point the main burners will ignite. This will
also supply the computer with a heat feedback sig-
nal. (It is the lack of this Feedback signal that causes
the Computer to display "Ignition Failure".)
• Each Ignition Control Module will spark for 10 sec-
onds and then check for a flame sense signal from
the Flame Rod. If the Ignition Control Module does
not see a flame sense signal it will "Lock Out".

Heating System - Split Vat:

• Power to the machine is turned ON:
• The computer is supplied with 24 VAC and, if the
Drain Valve Handle is closed, the Proximity Switch
will supply 24 VAC to the DVI (Drain Valve Inter-
lock) Input at the computer. The Ignition Control
Modules are also supplied with 24 VAC at the 24
V terminal.
• The computer is turned ON.
• Computer calls for heat and supplies 24 VDC to
the Heat Demand Relay which will energize supply-
ing the Blower Relay and the Pressure Switch with
power. When the Blower Relay energizes the Blower
will be supplied with power and will increase in speed
until the pressure switch closes.
• Before the pressure Switch closes it will supply
power to the Check Blower Relay which will re-
main energized.
• When the Pressure Switch comes up to speed it will
supply power to the second set of switch points on
the Check Blower Relay. Because the Check Blower
Relay is energized the Blower OK Relay coil will be
supplied with power causing it to energize. When
the Blower OK Relay energizes, one set of its Switch
points supplies voltage to the Left Hand Ignition
Control Module at the TH terminal and the other
set of switch points supplies the right hand Ignition
Control Module with power at the TH terminal. The
same power that is supplied to the TH terminals of
the Ignition Control Modules is also supplied to the
Hi Limit switches which, if closed, will supply power
to the Pilot Solenoid of the Gas Valve.
• When an Ignition Control Module is supplied with
power at the TH terminal it will supply power to the
Ignitor, the Main Solenoid of the Gas Valve and the
Heat Feedback Input of the Computer. (It is the
lack of this Feedback signal that causes the Com-
puter to display "Ignition Failure".)
• The Ignition Control Module will continue to spark
for 10 seconds and then look for a flame sense sig-
nal from the Flame Rod. If the Ignition Control
Module does not see a flame sense signal it will "Lock
Out".
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