Carrier 69UG15 manual Control Circuit Operation, Sequence of Operation a. Standard Units

2.4 CONTROL CIRCUIT OPERATION

WARNING

Beware of moving poly V-Belt and belt driv- en components.

2.4.1Sequence of Operation a. Standard Units

With the intake heater switch (IH) held in the ON position, current flows through the ammeter to the intake heater. While heater is on, the ammeter will show a 40--amp draw.

A second set of contacts also energizes the safety relay

(S).

If the high water temperature switch (HWT) opens to break the safety relay ground connection, the safety relay will not energize, and the engine will not start,

To start the engine, the ignition switch (IGN) is held in the START position. With the switch in the START position, current flows to the start solenoid (SS), through the SS contacts to the starter motor (SM). Current then flows to the intake heater timer, intake heater relay (IHR) and to the heater, while simultaneously powering the electronic governor module (EG), fuel solenoid (FS), and engine speed sensor (ESS).

The starter motor turns over the engine resulting in pumping of fuel to the engine cylinders by the injection pump. This fuel is ignited by heat of compression; thus starting the engine. When the engine has developed sufficient oil pressure, the low oil pressure switch contacts close to maintain power to the safety relay.

Once the engine has started, the intake heater will remain energized for 3 minutes.

The ignition switch (IGN) will be released. The intake air heater switch (IH) will be held for 5 seconds, then released after the IGN switch is realeased. When the START switch is released, the starter will be disengaged.

With the engine running, the battery charger provides DC power to operate the control system and charge the battery.

b. Units with Auto Start

When the ignition switch is placed in the RUN position, 12-volt DC power is applied to the low coolant sensor (LCS) and the auto restart module simultaneously. If the coolant level is below the sensor, all the indicator lights on the auto restart module will blink once and the LCS will open the contacts on the low coolant relay, de-energizing the unit’s 12-volt DC circuitry. If the coolant level is above the sensor, the auto restart module will maintain power and all lights on the module will illuminate. As the module performs its self test, the lights will go out individually.

After the self test is complete, the module will energize the intake heater and sound the audible alarm warning, indicating that the unit has been powered on and will start. The 30--second delay starts at this time. When the 30--second delay expires, power will be applied to the electronic governor and the engine attempts to crank for 15 seconds.

When the engine starts, the intake heater will remain energized for 3 minutes; during this time, the engine/intake heater light and alarm will be energized, the shutdown/lockout time delay of 15 seconds will begin counting, and the starter will be disengaged. During the shutdown/lockout time delay at start up, the auto restart module will disregard the signals to the oil pressure and engine temperature inputs, and the Run sequence will begin (see Restart Procedure). If engine does not start, refer to Table 1.3 for auto restart sequencing.

T-343 2--4