HEAT PUMP LAB REPORTRIL 212/E MR. PEREZ

The heat pump is considered the most energy efficent, electrically operated HVAC system in the market. The heat pump is a year round heating and air conditioning system that uses refrigeration equipment to provide cooling/dehumidification and heating. The refrigerant in the system absorbs and moves heat from the outside and pumps into the house during winter operation. In summer operation, the heat pump absorbs heat from the inside of the house and pumps the heat to be discharged outdoors.

Joaquin Velez ID # 2174604/14/2009

MECHANICAL SEQUENCE OF OPERATION FOR AN AIR TO AIR HEAT PUMP

HEATING CYCLEThe compressor pumps out high pressure, superheated vapor. The vapor leaves the

compressor and the passes through the reversing valve. Refrigerant flows through the insulated, indoor line to the finned indoor coil. Air from the indoor blower removes heat from

the refrigerant vapor warming the indoor air and heating the house. When enough heat is removed, the vapor condenses into a high-pressure liquid. The liquid temperature is slightly warmer than indoor air temperature. This warm, high-pressure leaves the indoor coil, flows

through the small copper refrigerant liquid line, and exits the building. At the end of the liquid line, the refrigerant passes through a metering device into the outdoor coil, reducing its

pressure and temperature. As the cool liquid, under reduced pressure, enters the outdoor coil surface, it expands and absorbs heat from the outdoor air passing over the finned surface.

Heat, from the outdoor air, causes the low-pressure liquid to evaporate. The refrigerant is now a cold vapor. The cold refrigerant vapor travels through the larger, outdoor vapor line into the

4-way reversing valve. The reversing valve directs the refrigerant into the accumulator. The accumulator holds liquid refrigerant and refrigerant oil and controls their flow back to the

compressor. They flow out through a small port inside the accumulator bottom. Refrigerant vapor flows through the suction line to the intake of the compressor. The cycle then repeats

until the Thermostat is satisfied

COOLING CYCLESystem operation is basically the same as during the heating cycle. The main difference is

the position of the reversing valve that reverses the flow of refrigerant. Setting the thermostat to the cooling mode automatically powers the solenoid valve in the reversing valve. The

compressor pumps out high-pressure, superheated refrigerant vapor. The vapor leaves the compressor and passes through the reversing valve. It flows through the outdoor vapor line to

the finned outdoor coil. Air from the outdoor fan removes heat from the refrigerant vapor. When enough of the latent heat is removed, the vapor will condense into a high-pressure

liquid. The liquid temperature is slightly warmer than ambient air temperature. This warm, high-pressure liquid leaves the leaves the outdoor coil, and flows through a metering devices, reducing its pressure and thus its temperature. As the liquid, under reduced pressure, enters

the indoor coil surface, it expands and absorbs heat from the indoor air passing over the finned surface. Heat, from the indoor air, causes the low-pressure liquid to evaporate and cools the

indoor air. The refrigerant is now a low pressure, low temperature cool vapor. The refrigerant vapor travels through the insulated vapor line to the 4-way reversing valve. The reversing valve

directs the refrigerant into the accumulator. The accumulator stores liquid refrigerant and refrigerant oil flow back into the compressor. Refrigerant vapor flows through the suction line

to the compressor. The cycles will then repeat until the Thermostat is satisfied.

DEFROST CYCLEIn the system heating mode the outdoor coil is the evaporator. Moisture from

the outdoor air condenses on the cooler coil and normally runs off. During the colder part of the heating season, this moisture freezes and blocks air movement

through the coil. This frost is removed in the defrost cycle. The heat pump operates in the heating mode. The defrost control detects the buildup of ice on the outdoor coil. The reversing valve solenoid energizes, directing hot gas from

the compressor to outdoor coil to defrost. The outdoor fan stops. If it didn’t, cold air from the fan would prevent the melting effect of the hot refrigerant gas from taking effect. As the temperature of the indoor air drops, controls energize the

electric heat elements to warm the indoor air. When the defrost control detects the ice has melted, it terminates the defrost mode. The reversing valve shifts to

the heating position and directs hot refrigerant gas to the indoor coil. The out fan operates. The elements cycle off. The unit is now in the normal heating mode.

ELECTRICAL SEQUENCE OF OPERATION FOR AIR TO AIR HEAT PUMPS

COOLING CYCLESetting the thermostat to the cooling mode automatically powers the reversing valve

solenoid. When the thermostat calls for cooling. This will send a 24-volt signal through the “Y” terminal to the compressor contactor located the outdoor unit. The compressor and the outdoor fan start. At the same time a 24-volt flows through the ‘G’ Terminal to the indoor blower relay. The indoor blower motor starts. The cooling system is now in operation. When the thermostat reaches its set-point it will open and end the call for cooling. This will interrupt the 24-volt signal to the compressor contactor and the outdoor unit stops. The system is now off.

HEATING CYCLEWhen the thermostat is set of heating mode a drop in temperature will cause the

thermostat to close. The thermostat calls for first stage heat. This sends a 24-volt signal through the “W1” terminal to the compressor contactor in the outdoor unit. The compressor and outdoor fan start. At the same time a 24-volt signal flows through the ‘G’ terminal to indoor blower relay. The indoor blower starts. The heating system is now in operation. If first stage heating is not enough to heat the house, the second stage thermostat bulb makes call for second stage heat. A 24-volt signal flows through the ‘W2’ terminal to the heating relay in the indoor air handler. This sequencing relay cycles on electric heating elements to add more heat to the indoor air steam. As the house warms, the second stage call for heat ends. This breaks the 24-volts to the “W2’ terminal and de-energizes the heating relay. The electric heating elements cycle off. The first stage thermostat call satisfies and ends the call for heat. This ends the 24-volt signal to the compressor contactor and the outdoor unit stops. This ends the 24-volt signal to the indoor blower relay and its stops. The system is now off. The reversing valve pilot solenoid stays de- energized as long as the thermostat is set for heating.

DEFROST CYCLE The defrost control timer will initiate a defrost cycle when ice builds up on the outdoor coil.

In order for defrosting to occur the Defrost thermostat must be closed. The control energizes the defrost relay coil with 24-volts. Immediately after the Defrost relay DR coil is energized the DFR contacts will change position. The defrost relay DFR 1 will open its N.C contacts to break power to the outdoor fan. The N.O DFR2 which is connected in parallel with the contact DT1 will close and is used as a holding contact around DT1. The N.O DF3 contacts close to energize the reversing valve. The system is now in cooling mode. Hot gas is now being sent to the outdoor coil to melt the buildup ice covering the outdoor coil. After the ice is defrosted, the defrost control terminates the defrost cycle by de-energizing the defrost relay. The defrost cycle is permitted to continue in its defrost cycle until the Defrost thermostat is satisfied and opens the circuit, or when the Defrost timer causes the DT 2 contact to open to de-energize the Defrost relay coil. Upon the de-energization of the Defrost relay, DF1 contacts will return to its N.C position sending power to the outdoor fan The defrost relay contacts DFR3 opens de-energizing the reversing valve and the valve returns to the heating position.. The defrost relay contacts open breaking 24 volt power to the indoor heating relay. The heat pump is now in the normal heating mode.

HEAT PUMP LAB REPORT

TROUBLESHOOTING THE HEAT PUMPFOR EACH OF THE FOLLOWING CONDTIONS GIVE CONSUMER COMPLAINT

1- THE CHECK VALVE IN THE INSIDE COIL IS STUCK IN THE CLOSED POSITION .

HOW IS THE LOW PRESSURE AND THE HIGH PRESSURE IN THE COOLING MODE?THE PRESSURE IS HIGH GOING TO OUTDOOR CIOL AND LOW GOING INTO THE INDOOR CIOL AND

COOLING MODE IS OPERATING NORMALLY. CUSTUMER COMPLAINT: NONE

HOW IS THE LOW PRESSURE AND THE HIGH PRESSURE IN THE HEATING MODE?THE PRESSURE IS LOW GOING TO OUTDOOR CIOL AND HIGH GOING INTO THE INDOOR COIL AND

HEATING MODE IS OPERATING ABNORMALLY. CUSTUMER COMPLAINT NO HEATING

2- THE CHECK VALVE IN THE OUTSIDE COIL IS STUCK IN THE CLOSED POSITION.

HOW IS THE LOW PRESSURE AND THE HIGH PRESSURE IN THE COOLING MODE?THE PRESSURE IS HIGH GOING TO OUTDOOR CIOL AND LOW GOING INTO THE INDOOR CIOL AND

COOLING MODE IS OPERATING ABNORMALLY. CUSTUMER COMPLAINT: NO COOLING

HOW IS THE LOW PRESSURE AND THE HIGH PRESSURE IN THE HEATING MODE?THE PRESSURE IS HIGH GOING TO INDOOR CIOL AND LOW GOING INTO THE OUTDOOR COIL AND

HEATING MODE IS OPERATING NORMALLY. CUSTUMER COMPLAINT: NONE

3- THE CHECK VALVE IN THE INSIDE COIL IS STUCK IN THE OPEN POSITION.

HOW IS THE LOW PRESSURE AND THE HIGH PRESSURE IN THE COOLIING MODE?THE PRESSURE IS HIGH GOING TO OUTDOOR CIOL AND HIGH GOING INTO THE INDOOR CIOL AND

COOLING MODE IS OPERATING ABNORMALLY. CUSTUMER COMPLAINT: NO COOLING, UNIT SHUTTING OFF

HOW IS THE LOW PRESSURE AND THE HIGH PRESSURE IN THE HEATING MODE?THE PRESSURE IS HIGH GOING TO INDOOR CIOL AND LOW GOING INTO THE OUTDOOR CIOL AND

HEATING MODE IS OPERATING NORMALLY. CUSTUMER COMPLAINT: NONE

4- THE CHECK VALVE IN THE OUTSIDE COIL IS STUCK IN THE OPEN POSITION .HOW IS THE LOW PRESSURE AND THE HIGHE PRESSURE IN THE COOLING MODE?

THE PRESSURE IS HIGH GOING TO OUTDOOR CIOL AND LOW GOING INTO THE INDOOR CIOL AND COOLING MODE IS OPERATING NORMALLY. CUSTUMER COMPLAINT: NONE

HOW IS THE LOW PRESSURE AND THE HIGHER PRESSURE IN THE HEATING MODE?THE PRESSURE IS HIGH GOING TO INDOOR COIL AND HIGH GOING INTO THE OUTDOOR CIOL AND

HEATING MODE IS OPERATING ABNORMALLY. CUSTUMER COMPLAINT: NO HEATING, UNIT TURNING OFF

HEAT PUMP

A DESCRIPTION OF ALL THE COMPONENTS

A- TWO STAGE THERMOSTAT : A device which detects temperature changes and initiates the system components involved with the heating or cooling operating of the system.This thermostat has 2 mercury filled bulbs which is arranged to contain two separate mercury contacts. This thermostat has been designed so that one of the contacts will make a call for heat before the other. . The first mercury contact starts the compressor and the fans. If more heat is demanded to heat the space then auxiliary heaters will be energized by the closing the circuit of the second mercury.

B- THERMOSTATIC EXPANSION VALVE: A specialized valve used in refrigerant systems to control the superheat in an evaporator by metering the liquid refrigerant flow to the evaporator. The TXV is so devised that the liquid refrigerant will start evaporating the moment that it enters the evaporator. This is called the “Dry” expansion principle Heat pump units typically have 2 TXV’s installed in parallel to the each if the check valves. The TXV purpose is to monitor the suction line superheat and either increases or decreases the flow of refrigerant to the evaporator coil depending on the temperature of the superheat.

C- LIQUID LINE FILTER/DRIER - In a heat pump system there is a bi- directional filter that is used for moisture removal and to catch particulate matter from the flowing refrigerant.

D- COMPRESSOR -The same as any other typical air conditioner compressor. The only exception when used in a heat pump for heating we use a compressor with a COP (coefficient of Performance) average 3.5-1 which means that most heat pump operate with an efficiency during heating of 350%. This depends on our total heat of rejection or (THOR) meaning as the temperature falls so does the COP and each heat pump has a specific balancing point depending on the climate it was designed to operate in.

E- INDOOR AND OUTDOOR COIL - Are exactly the same size and capacity as each other. F- SUCTION LINE ACCUMULATOR - Is a safety device designed to prevent refrigerant flow to the

compressor. It also stores the excess refrigerant during heating mode due to the fact that the heat pump does not need as much refrigerant to operate in the winter weather.

G- DEFROST TIMER : Energized when the compressor is on. Is a cumulative defrost timer that is used to de-energize the outdoor fan motor and to energize the reversing valve into the cooling mode for defrosting of an iced up outdoor coil. When the heat pump is used in the heating mode the outdoor coil is acting as the evaporator. Any moisture present in the air will condense on the coil causing a buildup of frost reducing the air flow of air through the outdoor coil. Defrosting is done by disconnecting the outdoor fan motor and reversing the flow of refrigerant though the coil. Before the defrost timer can be activated the defrost thermostat must be activated first it is located on the outside coil and must be closed in order to start the defrost cycle.

H- DUAL PRESSURE CONTROL : Is located on the inside coil and maintains pressure control in the heating and the cooling modes it is more likely to open the line on low pressure since it sensing refrigerant flow of the indoor coil which is operating as the evaporator low pressure vapor, and on heating it is more likely to open the line on high pressure because it is sensing the high pressure associated with the condensing coil..

I- 4-WAY REVERSING VALVE : Is actually two valves built into one housing. The control wires control a small solenoid valve that has a very small piping that runs along the outside of the valve. Its

position is determined by the solenoid. In most systems the 4-way reversing valve fails in the heating mode and that is how most troubleshooting and consumer complaints will be answered as if we fail in heating (not energized) the valve movement is controlled by pressure difference on a piston within the large portion of the valve. In the cooling mode the solenoid valve will be energized the pressure is now applied though the other end to the piston and the valve slides to the right. In the heating mode the solenoid is not energized, high pressure from the compressor pushes through the tubes of the pilot valve. This exerts a pressure on the right side of the slide pushing it to the left. The refrigerant on the left side is pushed back through the pilot valve and to the compressor suction line. In this position you are in heating mode to the inside of the coil.

J- CHECK VALVE - allows refrigerant to flow in only one direction. Check valves are two-port valves, meaning they have two openings in the body, one for fluid to enter and the other for fluid to leave.

K- ACCUMULATOR - A shell device installed in the suction line of a heat pump system to prevent liquid refrigerant from entering the compressor.

L- INTERNAL OVERLOAD : Thermal overload protection prevents compressor from overheating by using lock-out thermal relay and compressor motor temperature.The overload is a safety device that prevents the compressor from starting when:* the refrigerator is unplugged or disconnected then reconnected before refrigerant pressures have a chance to equalize* the compressor body is too hot* when start up of the compressor draws too much current due to:* voltage too low* internal electrical problem* internal mechanical resistance* refrigerator is stored outdoors, compressor too cold

M- START RELAY (CURRENT TYPE) : This current type starting relay contacts are normally open and is used for a single-phase AC induction motor. This starting relay is an electrically operated switch in which the coil of the relay is connected in series with the run winding of the compressor motor. Current flowing through the coil of the relay creates a magnetic field which attracts a lever and changes the switch contacts. The coil current can be on or off so relays have two switch positions and they are double throw switches. The function of the start relay is to momentarily energize the start winding in the compressor motor and then cut power to the start winding as soon as the motor has reached about 75% of its full speed.

How it works: It is a current-sensing relay, which utilizes the principal of electromagnetism in a solenoid coil to be actuated by the motor main winding current through the coil, opening and closing the contacts of the relay. The relay utilizes the current of the main-winding current and motor speed to actuate the contacts to energize and de-energize the start winding circuit. As the motor accelerates and the main winding current increases, the relay solenoid picks up and closes the contacts to the start winding circuit. As the motor increases its speed, the main winding current begins to decrease, and at the appropriate motor speed (about 75% of its full speed.) the relay drops out, allowing the contacts to open and disconnect the start winding from the circuit. Gravity acting on the plunger opens the contacts.

N- INDOOR FAN MOTOR : A forced convector used to improve the efficiency of an outdoor heat exchanger by air movement over the coil.

O- OUTDOOR FAN MOTOR : A forced convector used to improve the efficiency of an outdoor heat exchanger by air movement over the coil.

P- AUXILARY HEATER ELEMENT -

3- IN ALL THE FOLLOWING CONDITIONS GIVE THE COSTUMER COMPLAINT AND THE PROMBLEM FOUND. YOU MUST WRITE DOWN THE COMPLETE TROBLESHOOTING PROCEDURE YOU WENT THROUGH TO ITENTIFY THE PROMBLEMS.

(A) DFR1 WILL NOT OPEN(B) DT1 WILL NOT CLOSE(C) DT2 WILL NOT OPEN

(D) DFR2 WILL NOT CLOSE(E) DFR3 WILL NOT CLOSE

(F) OPEN COIL ON CONTACTOR(G) OPEN COIL ON TIMER MOTOR

(H) OPEN COIL REVERSING SOLENOID

HEAT PUMP ELECTRICAL TROUBLESHOOTING

(A) DFR1 WILL NOT OPEN

CUSTOMER COMPLAINT: SIGNIFICANT REDUCTION IN HEATING OR LOW HEATPROMBLEM: The DFR1 is a normally closed contact in series with the Fan motor relay. If when the

Defrost timer calls for defrosting then when the DFR coil is energized then the N.C contact in series with the Fan relay will not open then there is a problem. The Fan will be energized during the System defrost cycle.

TROUBLESHOOTING PROCEDURE:

(B) DT1 WILL NOT CLOSECUSTOMER COMPLAINT: NO HEATING OR TURNS OFF SUDDENLYPROMBLEM: DT1 is a N.O contact that is supposed to close before DT2 opens. IF DT1 does not close

than the defrost relay would never energize to close DT3 thus, defrost would never occur.TROUBLESHOOTING PROCEDURE:

(C) DT2 WILL NOT OPEN

CUSTOMER COMPLAINT: The unit will remain in defrost cycle until the Defrost thermostat is satisfied and opens the circuit, of the Defrost timer caused the

PROMBLEM:TROUBLESHOOTING PROCEDURE:

(D) DFR2 WILL NOT CLOSECUSTOMER COMPLAINT: DFR2 acts like a holding contact ergiPROMBLEM:TROUBLESHOOTING PROCEDURE:

(E) DF3 WILL NOT CLOSECUSTOMER COMPLAINT:

PROMBLEM: DFR3 contacts are supposed to close to send power to the reversing valve solenoid. If DFR3 contacts don’t close then no hot gas will be sent to the outdoor coil to melt of the buildup of ice.

TROUBLESHOOTING PROCEDURE:

(F) OPEN COIL AT CONTACTORCUSTOMER COMPLAINT: NO COOLING OR HEATINGPROMBLEM: Compressor will not turn and the outdoor fan will not turn on.TROUBLESHOOTING PROCEDURE: My first objects of interest were the compressor and condenser

fan motor. First I set the thermostat for heating operation. I checked for applied voltage with the voltmeter across the compressor and the condenser fan motor. I got O volts. I then knew a normally open CC switch has not close due to the fact that I set the unit for operation. I used my voltmeter to test the cc coil and I got the applied voltage of 24 volts. I then determined that the switch was giving me applied voltage but the cc contacts were not closing in order to energize the compressor and the outdoor fan motor.

(G) OPEN COIL ON TIMER MOTORCUSTOMER COMPLAINT: PROMBLEM: The Defrost timer will never initiate a call from defrosting due to an open coil. The

defrost relay will never be energized and system defrost will never occur.TROUBLESHOOTING PROCEDURE:

(H) OPEN COIL REVERSING SOLENOIDCUSTOMER COMPLAINT: HEATING BUT NO COOLINGPROMBLEM: In most heat pump units the 4- way reversing will fail in the heating mode. If the

reversing valve solenoid coil is open the unit will only be able to provide heating but no cooling.TROUBLESHOOTING PROCEDURE: I set the thermostat for cooling operation. I did not hear a sound

consistent with the energization of a solenoid. Did a voltage reading across solenoid I got 24 volts. Meaning that the solenoid will give applied voltage when it is energized. But in this case the solenoid is energized during two applications during cooling.