2 Speed+Compressor LAB REPORT

Lennox ST-202 speed compressor trainer

MECHANICAL COMPONENTS:

2 SPEED COMPRESSOR: A vapor pump that pumps refrigerant throughout the system at a high pressure and returns the refrigerant vapor at a lower pressure. This two speed compressor motor operates at a low speed on 3-phase 208/230 of power being completed into a series ‘Y’ configuration on 4 poles at 1800. At high speed 3-phase 208/230 of power are being completed into a parallel ‘Y’ configuration on 2 poles at 3600 RPM.

CONDENSER: Component of the system which transfers the heat from the load by condensing the refrigerant.

EVAPORATOR: System component which absorbs the heat of the load into the system by evaporation of the refrigerant.

ELECTRICAL COMPONENTS

PROTECTION MODULE: The protection module is connected to sensors within the compressor motor windings through terminal S1 and S2. If an excess of winding temperature is detected the module will break the compressor control circuit between terminals K1 and K2 which will de-energize the compressor.

TRANSFORMER- 208/230 PRIMARY / 24 SECONDARY 70Va 3.2 Amp

A system component which changes values in voltage, current and impedance without a change in frequency. Either to a higher value (a step-up transformer) or to a lower value (a step-down transformer).

How it works: Through the primary and secondary windings of the device the voltage, current or impedance is transferred by magnetic induction

CURRENT LIMITING DEVICE: The current limiting device indicated as (RT) is a negative temperature coefficient thermister (NTC). An increase in temperature equals degrees in resistance. The (NTC) thermister absorbs the current surge created. When the potential relay contacts close and discharge the run capacitor. This prevents the relay contact from welding.

COMPRESOR INTERLOCK- Prevents compressor fast cycling provides a nominal 71 time delay between cycles. Delay time may range from 60 to 96 seconds. The voltage input is 20 VAC to 30 VAC max. Rest time is 0.016 second max.

CONTROL RELAYS: The control relays are 24v, K! For low speed and K@ for high speed.

ROOM 2-STAGE THERMOSTAT: Component which initializes the control circuit. Uses a mercury filled bulb and a spiral shaped bi-metallic strip to sense the changes in heat in a room. This thermostat has two-stage cooling and single stage heating. The system Selector is (OFF-HEAT-AUTO-COOL) and fan control switch is (AUTO-ON)

FAN RELAY: The fan relay K3 is used to turn on the condenser fan motor when the system is on and the crankcase heater when the system is off.

TIME DELAY: The K7 time delay provides a time delay between compressor speeds to allow the compressor to completely stop. Time delay is set for 20 to 40 second and the off time is 30 to 50 seconds.

CRANKCASE HEATER THERMOSTAT: The crankcase heater thermostat opens at 101 degrees F Fahrenheit and closes at 81 degrees F. This thermostat disconnects power to the crankcase heater at temperatures above its set point.

HIGH PRESSUR SWTCH: A pressure activated switch which detects the amount of pressure in the high side of the system. A safety device that provides protection to the compressor by shutting down the system on high pressure. This switch is mounted on the discharge line; it opens the control circuit if the pressure becomes too excessive. It has a cut-out pressure of 410 psig and a reset of 180 psig. The reset is manual.

LOW PRESSURE SWITCH: A pressure activated switch which detects the amount of pressure in the low side of the system. A safety device that provides protection to the compressor by shutting down the system on low pressure.

The switch is mounted in the suction line; it opens the control circuit if the pressure goes to low. It has a cut out pressure of 25 psig and an automatic cut in pressure of 55 psig.

START CAPACITOR: A capacitor that is used to help improve the starting torque of an AC induction motor.

RUN CAPACTIOR-The run capacitor is used to bring the inductive circuit produced by a compressor motor back into phase and reduce the current drain from the power source. This aids in keeping down operating cost for electricity. It stays in the circuit as long as the motor will run.

COMPRESOR INTERLOCK- Prevents compressor fast cycling provides a nominal 71 time delay between cycles. Delay time may range from 60 to 96 seconds. The voltage input is 20 VAC to 30 VAC max. Rest time is 0.016 second max.

COMPRESSOR CONTACTOR-The HS12 combination contactor with two coils, K5 with 5 poles and K4 with 2 poles. Two normally closed (N.C) auxiliary switches are integral to the contactor, one on the K4 side and one the K5 side. The K4 and K5 sections are mounted to a common base plate and mechanically interlocked to prevent simultaneous operation. The auxiliary switches are used to electrically interlock the contactor coil and to prevent simultaneous operation. The electrical and mechanical interlocks protect against any condition that

LOW-PRESSURE CONTROL: A pressure activated switch which detects the amount of pressure in the low side of the system. A safety device that provides protection to the compressor by shutting down the system on low pressure.

EVAPORATOR FAN MOTOR: A forced convector used to improve the efficiency of an evaporator by air movement over the coil. A RSIR motor so no capacitors are needed.

CONDENSER FAN MOTOR: A forced convector used to improve the efficiency of a condenser by air movement over the coil.

ELECTRICAL SEQUENCE OF OPERATION

On a call for cooling the rise in temperature will cause the thermostat switch 1st stage contacts to close. 24 volts of power is now being sent to the EFR coil through the “G’ terminal this will cause the N.O open IBR contacts to close and to energize the evaporator fan motor with 208/230 volts of power. Current will also flow simultaneously to terminal (YI) across the K1 relay coil through the N.C K7 contacts and will complete a circuit back to power. The energize K1 relay coil will cause all the N.O K-1 contact to close completing a circuit on the 24v protection module. The completed made by closing all the the N.O K1 switch will complete a circuit drawing power from terminals (P1-K2) and across both K3 and K4 relay coils then across contacts K1,K5,K2 and the LPC and HPC safety switches then through terminals (K1-P2) on the power module and then back to power. The energized K3 relay coil with 24 of power will close the N.O K3 contacts and this will power the condenser fan motor(CFM) with 208/230 volts of power. When the interlocked K3 coil is energized, the N.O K3 switches will close and the N.C K3 switches controlling the crankcase heater (CCH) will open and de-energize the CCH .The energized K4 relay coil will cause three of the N.O K4 contacts to close and will in turn will energize the compressor circuit. Now 3-phase 208/230 of power is being completed into a series ‘Y’ configuration. The compressor is now running on 1st stage low speed. The Condenser Fan and Compressor Motor are now ON. The refrigeration cycle has now begun.

When the 2nd stage thermostat closes power will go through terminal ‘R” across the 2nd stage contacts to energize the K2 relay coil with 24 volts of power. The energized K2 relay coil will cause two N.C contacts to open (K1, K1-1) and two N.O contacts to close (K2, K2-2) in the circuit in the protection module. Power has now been interrupted to the K3 and K4 relay coils this will cause the condenser fan motor (CFM) and the compressor motor (CM) to de-energize.

The N.O K2-1 contacts are now closed completing a circuit that will energize the time delay relay coil (K7). The time between cycles will be in between 20 to 40 seconds. After the time delay period has ended the N.C K7 contacts on the 1st stage room thermostat will open and de- energize the K1 relay coil. The de-energized K1 relay will cause the N.C K1 contact to open and the K1-1 contact to change positions within the circuit. The N.O K7 contacts after the delay period will close. Now a circuit is completed across the terminal P1-K2 to the K3 relay coil and the K5 relay coil through the contacts K1-1, K7, K4-2, K2-1 through the LPC and HPC safety switches then through the terminal K1-P2 on the protection module back to power. The energisation of the K3 relay coil with 24 of power will close the N.O K3 contacts and this will power the condenser fan motor(CFM) with 208/230 volts of power. The energized K5 relay coil will cause five of the N.O K5 contacts to close and will energize the compressor circuit. Now 3-phase 208/230 of power is being completed into a parallel ‘Y’ configuration.

The compressor is now running on 2nd stage high speed. When the interlocked K-3 coil is energized, the N.O K3 switches will close and the N.C K3 switches controlling the crankcase heater (CCH) will open and de-energize the CCH. The Condenser Fan and Compressor Motor are now ON. The refrigeration cycle has now begun. When the room thermostat detects the set point temperature in the room has reached the desired set- point temperature the 2nd stage thermostat contact will open and de-energizes the K2 relay coil and to the IBR relay coil. The de-energized IBR coil will open the closed IBR contact in series with the Evaporator fan motor. The EFM is now de-energized. The de-energized K2 relay coil will cause all of the K2 switches to return to their N.C positions (K2-1, K2-2). This will interrupt power to the K3 and K5 relay coils. This will cause all N.O switches of the of K3 and K5 coils to open. The five N.O K5 contacts will open de-energizing the compressor motor. When the interlocked K3 coil is de- energized, the N.O K3 switches will close and the N.C K3 switches controlling the crankcase heater (CCH) will close and energize the CCH. The Condenser Fan is now OFF. The Compressor is now OFF. The refrigeration cycle has now ended.

FAULT NUMBER: ___________.

A.CUSTOMER COMPLAINT:

____________________________________________________________________________________________________________________

B. Thermostat mode: HEATING_____________ COOLING______________ OFF_________________

FAN SWICH: AUTO___________ ON______________

TEMPEPERATURE SETTING ______________F

C.ROOM TEMPERATURE: ______________F

D.OBSERVATION:

_________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________

E. TEST(S) MADE AND METER USED FOR TEST PROCEDURE:

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F.CONCLUSION:

________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________

G. REPLACEMENT(S) REQUIRED:

____________________________________________________________________________________________________________________

H. TIME REQUIRED TO FIND FAULT:

_____________________________________________________________________________________________________________________

FAULT NUMBER: 1

A.CUSTOMER COMPLAINT: NO COOLING

B. Thermostat mode: COOLING

C. Room Temperature: 72 Degrees F

D. Observation:

On turning on the unit I observed that the EFM was energized. But the condenser fan and compressor did not turn on neither for low speed or for high speed operation.

E. Test made and meter used for test procedure

My initial objects of interest were the condenser fan motor and the compressor mot0r because they were not being energized like they would be on a normal operation sequence. Set the room thermostat for cooling, set the temperature for low speed operation. I used a voltmeter and tested the following contacts K-2-1, K2-2, K5-2, and K1-1. I got 0 volts on all these contacts. Tested the K3 relay coil for voltage drop, I read O volts. A test for voltage drop across K4 also read 0 volts. Tested voltage a points 1 and K1 got 0 volts. Tested for voltage across the N.C switch between points P2 and K1 the meter the read 24 volts. I then used an ohmmeter to test the sensors of the power module. In between terminals S1 and S2. The ohmmeter gave a reading of 27.4 ohms.

F. Conclusion:

The power module switch in between terminal p2 and K1 is open. The ohmmeter gave a reading of 27.4 ohms.

G. Replacement(s) Required:

New power module

H. Time required to find fault:

10 min

FAULT NUMBER: 2

A.CUSTOMER COMPLAINT: NO COOLING



D. Observation:


E. Test made and meter used for test procedure.

My initial objects of interest were the condenser fan motor and the compressor motor because they were not being energized like they would be on a normal operation sequence. Set the room thermostat for cooling, set the temperature for low speed operation. I used a voltmeter and tested the following contacts K-2-1, K2-2, K5-2, and K1-1. I got 0 volts on all these contacts. Tested the K3 relay coil for voltage drop I read O volts. A test for voltage drop across K4 also read 0 volts. Tested voltage across points 1 and K1 got 24 volts.

F. Conclusion:

Either an open LPS or HPS.


I would not go into a haste judgment and say that a replacement of the HPC or LPC is needed. Maybe a genuine problem with the refrigeration circuit could have manifested itself in order to cause one of the pressure switches to open. After checking the operating pressures in the field I would check to see if the cause was a legitimate refrigeration problem or a defective pressure switch.


2 min

FAULT NUMBER: 3

A.CUSTOMER COMPLAINT:

B. Thermostat mode: LOW COOLING


D. Observation:



My initial objects of interest were the condenser fan motor and the compressor motor because they were not being energized like they would be on a normal operation sequence. Set the room thermostat for cooling, set the temperature for low speed operation. I used a voltmeter and tested the following contacts K-2-1, K2-2, K5-2, and K1-1. I got 0 volts on all these contacts. Tested the K3 relay coil for voltage drop I read O volts. A test for voltage drop across K4 also read 0 volts. Tested voltage across points 1 and K1 got 24 volts. Tested for voltage across the N.C switch between points P2 and K1 the meter the read O volts. I then used an ohmmeter to test the sensors of the power module. In between terminals S1 and S2. The ohmmeter gave a reading of 5.11 ohms.

F. Conclusion:

K-1 relay coil is open that is why there is cooling on high speed but not on low speed.


Defective relay must be replaced with one with same exact specifications.


15 min

FAULT NUMBER : 4

A.CUSTOMER COMPLAINT: INSUFFICANT COOLING OR HIGH SPEED COOLING DOES NOT WORK



D. Observation:



My initial objects of interest were the condenser fan motor and the compressor motor because they were not being energized like they would be on a normal operation sequence. Set the room thermostat for cooling, set the temperature for low speed operation. I used a voltmeter and tested the following contacts K-2-1, K2-2, K5-2, and K1-1. I got 0 volts on all these contacts. Tested the K3 relay coil for voltage drop I read O volts. A test for voltage drop across K4 also read 0 volts. Tested voltage across points 1 and K1 got 24 volts. Tested for voltage across the N.C switch between points P2 and K1 the meter the read O volts. I then used an ohmmeter to test the sensors of the power module. In between terminals S1 and S2. The ohmmeter gave a reading of 5.11 ohms.

F. Conclusion:



FAULT NUMBER: 5

A.CUSTOMER COMPLAINT: INSUFFICAINT COOLING OR NO HIGH SPEED



D. Observation:

On turning on the unit low speed I observed that it when through its normal operating sequence. Evaporator fan on. Condenser Fan On . Compressor on. However an attempt to start high speed operation after the time delay was suppose initiate high speed operation the evaporator fan was energized but the condenser fan motor and compressor motor failed to be energized in sequence.

E. Test made and meter used for test procedure:

My initial objects of interest were the condenser fan motor and the compressor motor because they were not being energized like they would be on a normal operation sequence. Set the room thermostat for cooling, set the temperature for high speed operation. I used a voltmeter and tested the following contacts K-2-1, K2-2, K5-2, and K1-1. I got 0 volts on all these contacts. Tested the K3 relay coil for voltage drop I read O volts. A test for voltage drop across K4 also read 0 volts. Tested voltage across points 1 and K1 got 0 volts. Tested for voltage across the N.C switch between points P2 and K1 the meter the read 24 volts. I then tested the voltage drop across the K-7 relay coil. The meter read 24 volts. Checked the voltage across the contacts of the N.C K-7 I got O volts. Across N.O K-7 I got 24 volts. Across the K-3 coil also I read 0 volts. I then used an ohmmeter to test for continuity of the K-7 time delay relay coil. I read infinity.

F. Conclusion:

An open coil in the time delay relay prevented the K-7 switches from changing position to engage the high speed of the compressor motor and also to turn the condenser fan on. That is the reason why the unit was stuck only on low speed functioning only .


New Time Delay relay

H. Time required to find fault: 20min

2 Speed+Compressor LAB REPORT

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