Carrier 30RAP010-060 specifications Service, Electronic Components, Unit Size 30RAP EXV Steps

circuits, the control will most often start the A1 or B1 compres- sor first, especially after long off periods. The MBB controls fan stages to maintain the head pressure set point and will auto- matically adjust unit capacity as required to keep compressors from operating outside of the specified envelope. There are no pumpout or pumpdown sequences on these chillers.

For all units, if temperature reset is being used, the unit con- trols to a higher leaving-fluid temperature as the building load reduces. If demand limit is used, the unit may temporarily be unable to maintain the desired leaving-fluid temperature be- cause of imposed power limitations.

SERVICE

WARNING

Electrical shock can cause personal injury and death. Shut off all power to this equipment during service. There may be more than one disconnect switch. Tag all disconnect locations to alert others not to restore power until work is completed.

Electronic Components

CONTROL COMPONENTS — Unit uses an advanced elec- tronic control system that normally does not require service. For details on controls refer to Operating Data section.

Access to the compressors is through latched panels from beneath the control box on all models or from opposite the coil side (sizes 010-030 only). The front door(s) provide access to the compressor(s) and all components of the refrigeration sys- tem. For size 010-030 units, access to the controls is through the upper latched outer door above the compressor access door. Similarly, the upper center latched door on sizes 035-060 gives access to the controls. Inner panels are secured in place and should not be removed unless all power to the chiller is off.

Electronic Expansion Valve (EXV) — See Fig. 24 for a cutaway view of the EXV. High-pressure liquid refriger- ant enters valve through the top. As refrigerant passes through the orifice, pressure drops and refrigerant changes to a 2-phase condition (liquid and vapor). The electronic expansion valve operates through an electronically controlled activation of a stepper motor. The stepper motor stays in position, unless power pulses initiate the two discrete sets of motor stator wind- ings for rotation in either direction. The direction depends on the phase relationship of the power pulses.

The motor directly operates the spindle, which has rotating movements that are transformed into linear motion by the transmission in the cage assembly. The valve includes a posi- tive shut-off when closed.

There are two different EXVs. See Table 30 for number of steps. The EXV motor moves at 200 steps per second. Com- manding the valve to either 0% or 100% will add extra steps to the move, to ensure the value is open or closed completely.

Table 30 — EXV Steps

UNIT SIZE 30RAP	EXV STEPS
010-020	1596
025,030	2500
035-045	1596
050-060	2500

The EXV board controls the valve. Each circuit has a thermistor located in a well in the suction manifold before the compressor. Suction pressure as measured by the suction pres- sure transducer is converted to a saturated suction temperature. The thermistor measures the temperature of the superheated gas entering the compressor and the pressure transducer

determines the saturated temperature of suction gas. The differ- ence between the temperature of the superheated gas and the saturated suction temperature is the superheat. The EXV board controls the position of the electronic expansion valve stepper motor to maintain superheat set point.

The MBB controls the superheat leaving cooler to approxi- mately 9° F (5° C). Because EXV status is communicated to the main base board (MBB) and is controlled by the EXV boards, it is possible to track the valve position. The unit is then protected against loss of charge and a faulty valve. Just prior to compressor start, the EXV will open. At low ambient tempera- tures the EXV is closed at start up. After initialization period, valve position is tracked by the EXV board by constantly mon- itoring the amount of valve movement.

The EXV is also used to limit cooler saturated suction tem- perature to 50 F (10 C). This makes it possible for the chiller to start at higher cooler fluid temperatures without overloading the compressor. This is commonly referred to as MOP (maxi- mum operating pressure). At ambient temperatures above 110 F, MOP is bypassed at start-up to prevent charge backup in the condenser.

If it appears that the EXV module is not properly control- ling circuit operation to maintain correct superheat, there are a number of checks that can be made using test functions and initialization features built into the microprocessor control. See the EXV Troubleshooting Procedure section to test EXVs.

EXV Troubleshooting Procedure — Follow steps below to diagnose and correct EXV/economizer problems.

Check EXV motor operation first. Switch the Enable/Off/ Remote Contact (EOR) switch to the Off position. Press ESCAPE on the Navigator™ display until ‘Select a menu item’ appears on the display. Use the arrow keys to select the Service Test mode. Press ENTER . The display will be:

		OFF
> TEST
	OUTS
	COMP

Press ENTER (password entry may be required) and use to change ‘OFF’ to ‘ON’. Switch the EOR switch to Enable. The Service Test mode is now enabled. Move the pointer down to the OUTS sub-mode and press ENTER . Move the pointer to item EXV.A or EXV.B as needed. Press ENTER and

the valve position will flash. Use to select 100% valve position (hold for quick movement) and press ENTER .

The technician should be able to feel the actuator moving by placing a hand on the EXV. A sight glass is located on the valve body to verify that the sleeve is moving to expose/cover slots in the orifice. A hard knocking should be felt from the actuator when it reaches the top of its stroke (can be heard if surround- ings are relatively quiet). Press ENTER again twice if necessary to confirm this. To close the valve, press ENTER , select 0% with and press ENTER . The actuator should knock when it reaches the bottom of its stroke. If it is believed that the valve is not working properly, continue with the checkout procedure below:

Check the EXV output signals at appropriate terminals on the EXV module (see Fig. 25). Connect positive test lead to red wire (EXV-J6 terminal 3 for Circuit A, EXV-J7 terminal 3 for Circuit B). Set meter to approximately 20 vdc. Using the Service Test procedure above, move the valve output under test to 100%. DO NOT short meter leads together or pin 3 to any other pin as board damage will occur.

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