Carrier 040-420 specifications Electronic Expansion Valve, Electronil c Expansion Valve EXV

1.

Electronic Expansion Valve

EXV OPERATION - These valves control the flow of liq- uid refrigerant into the cooler. They are operated by pro- cessor to maintain a specified superheat at lead compressor entering gas thermistor (located between compressor motor and cylinders). There is one EXV per circuit. See Fig. 11.

High-pressure liquid refrigerant enters valve through bot- tom. A series of calibrated slots are located in side of ori- fice assembly. As refrigerant passes through orifice, pres- sure drops and refrigerant changes to a 2-phase condition (liquid and vapor). To control refrigerant flow for different operating conditions, sleeve moves up and down over ori- fice, thereby changing orifice size. Sleeve is moved by a linear stepper motor. Stepper motor moves in increments and is controlled directly by processor module. As stepper motor rotates, motion is transferred into linear movement by lead screw. Through stepper motor and lead screws, 760 discrete steps of motion are obtained. The large num- ber of steps and long stroke result in very accurate control of refrigerant flow.

The biF\ subfunction shows EXV valve position as

a percent of full open. Position should change constantly while unit operates. If a valve stops moving for any reason (mechanical or electrical) other than a processor or ther- mistor failure, the processor continues to attempt to open or close the valve to correct the superheat. Once the calcu- lated valve position reaches 60 (fully closed) for 040-210 and associated modular units, 145 (fully closed) for 225, 250, and 280 units, or 760 (fully open) it remains there. If EXV position reading remains at 60, 145 or 760, and the thermistors and pressure transducers are reading correctly, the EXV is not moving. Follow EXV checkout procedure below to determine cause.

The EXV is also used to limit cooler suction temperature to 50 F (10 C). This makes it possible for chiller to start at higher cooler water temperatures without overloading com- pressor. This is commonly referred to as MOP (maximum operating pressure), and serves as a load limiting device to prevent compressor motor overloading, This MOP or load limiting feature enables the 30G FlotronicT’ II chillers to operate with up to 95 F (35 C) entering water temperatures during start-up and subsequent pull-down.

STEPPER

‘DC)

CHECKOUT PROCEDURE - Follow steps below to di- agnose and correct EXV problems.

1, Check EXV driver outputs. Check EXV output signals at appropriate terminals on EXV driver module (see Fig. 12) as follows:

Connect positive test lead to terminal 1 on EXV driver. Set meter for approximately 20 vdc. Enter outputs

subfunction of test function by pressing riF[ , then advance to EXVA test by pressing q 8 times. Press

T;ip--p-&q*The driver should drive the circuit A EXV fully open. During next several seconds connect nega- tive test lead to pins 2, 3, 4 and 5 in succession. Voltage should rise and fall at each pin. If it remains constant at a voltage or at zero v, remove connector to valve and recheck.

Press m H to close circuit A EXV. If a problem still

exists, replace EXV driver module. If voltage reading is correct, expansion valve should be checked. Next, test EXVB. Connect positive test lead to pin 7 and the neg- ative test lead to pin 8, 9, 10, 11 in succession during EXVB test.

2.Check EXV wiring, Check wiring to electronic expan- sion valves from terminal strip on EXV driver. See Fig. 12.

a.Check color coding and wire connections. Make sure they are connected to correct terminals at driver and EXV plug connections.

b.Check for continuity and tight connection at all pin terminals.

c.Check plug connections at driver and at EXVs to be sure EXV cables are not crossed.

E X V D R I V E R

BOARD - J4

I

O R I F I C E

ASSEMBLY (INSIDE PISTON

SLEEVE)

Fig. 11 - Electronil c Expansion Valve (EXV)

T

EXV - Electronic Expansion Valve

Fig. 12 - EXV Cable Connections to

EXV Driver Module, DSIO (EXV)

3.Check resistance of EXV motor windings. Remove plug at 54 terminal strip and check resistance between com- mon lead (red wire, terminal D) and remaining leads, A, B , C, and E (see Fig. 12). Resistance should be 25 ohms -1- 2 ohms.

Control of valve is by microprocessor. A thermistor and a pressure transducer located in lead compressor are used to determine superheat. The thermistor measures tem- perature of the superheated gas entering the compressor cylinders. The pressure transducer measures refrigerant pressure in the suction manifold. The microprocessor con- verts pressure reading to a saturation temperature. The difference between temperature of superheated gas and saturation temperature is the superheat.

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