Sait Racm Cntr 373 4Th: Oil Failure Control And Electromechanical Control (2024)

Front 1

Should the P28 oil failure control be mounted vertically?

Back 1

The P28 is not position sensitive

Front 2

Should the P28 be mounted with the dust cover off if it away from the compressor in an electrical box?

Back 2

No, keep the dust cover on

Front 3

Is there a P28 that is Ammonia Specific?

What are some of the mounting concerns with ammonia?

Back 3

Yes.

• A P28AN or P28DN control used for ammonia service must be mounted separately from the electrical cabinet.

An ammonia leak could damage the electrical circuitry.

• Do not use Johnson Controls/Penn

Ecosafe® hose tubing in applications with ammonia or other corrosive refrigerants. Corrosion could cause tube breakage and refrigerant leakage.

Front 4

Describe the operation of the P28

Back 4

When the compressor starts, the timer is energized because the net oil pressure of the system is zero.

During normal operation, the net oil pressure should build up to the pressure switch's cut-out setting (scale setting) plus the switch differential (3 to 5 psi [21 to 34 kPa]) within the required time delay, causing the time delay relay to de-energize.

If the net oil pressure does not rise to the cut-out pressure setting plus the switch differential within the required time delay, the time delay relay trips and stops the compressor.

If the net oil pressure drops below the cut-out pressure setting during the compressor's run cycle, the time delay relay energizes. If the net oil pressure returns within the time delay, the time delay relay de-energizes and the compressor continues to operate normally. If the net oil pressure does not return within the time delay, the control shuts down and locks out the compressor.

Front 5

What are some basic installation warnings with the P28?

Back 5

CAUTION: Equipment damage hazard.

Avoid sharp bends or kinks in the capillary or tubing to avoid damage to the capillary.

• Coil and secure excess capillary or tubing. Because harmonic vibration can break the capillary or tubing, some slack must be provided.

• Do not allow the capillary or tubing to rub against metal surfaces where friction can cause damage.

• When using a control with 1/4 in. / 6.4 mm tubing, a pulsation damper must be used. Pulsation can cause excessive wear and damage the control.

Front 6

On the test how will they tell you to test the oil failure control?

Back 6

Remove compressor from the load side of the contactor and then energize the circuit. This will turn on the contactor and eventually trip the P28.

Front 7

What does the P28 measure?

Back 7

The P28 and P128 controls measure the net oil pressure available to circulate oil throughout a pressure-lubricated refrigeration system.

The net oil pressure is the difference between the oil pressure at the pump discharge and the refrigerant pressure in the compressor crankcase.(suction)

Example: If the oil pressure pump discharge reading is 90 psi (621 kPa) and the crankcase pressure is 70 psi (483 kPa), the net oil pressure is 20 psi (138 kPa).

Front 8

What are the contacts between 1-2 and L-M normally open or normally closed?

Back 8

Both are N/C

Front 9

How should you set the oil differential is the manufacturers specification is not known?

Back 9

Back (Definition)

Front 10

Which contacts do you jumper to test the oil failure control (according to the P28 manual)?

Back 10

Contacts 1-2

Front 11

What does the wiring diagram look like? What is the opening force on the differential pressure switch?

Back 11

Back (Definition)

Front 12

What would happen if the heater inside the P28 failed?

Back 12

If the pump fails, the oil pressure control wouldnt work.

Front 13

How do you size fuse sizes?

Transformer VA: 100VA

Low side voltage: 24V

P=IV

(100VA)/(24V)= 4.16A

Max fuse size = 4.16A x 1.25

= 5.2A (choose smaller -> 5A)

Back 13

Transformer VA: 100VA

Low side voltage: 24V

Front 14

How do you size fuse sizes?

Transformer VA: 100VA

Low side voltage: 24V

P=IV

(100VA)/(24V)= 4.16A

Max fuse size = 4.16A x 1.25

= 5.2A (choose smaller -> 5A)

Back 14

Transformer VA: 100VA

Low side voltage: 24V

Front 15

What is a proportional signal?

Back 15

The control signal is not on/off. The signal will ask for a percentage of demand. Think of a gas pedal.

Front 16

What is the difference between opposed and parallel blades?

Back 16

Opposed blades work for proportional control: 50% open means 50% airflow (linear control)

Parallel don’t work for proportional control: 50% open means 90% airflow

Front 17

What are the two types of blade design? What are their fpm design speeds?

Back 17

Back (Definition)

Front 18

What installation specifications must be followed when installing a flow switch?

Back 18

TQ: Flow switch must me installed on a threaded tee or welded fitting (half coupling).

Front 19

Do the overloads on a motor control open contacts on the control circuit or the line voltage circuit?

Back 19

It opens the control circuit.

Front 20

What is a manual motor starter?

Back 20

It is used on fractional hp motor that is not internally thermally protected.

Looks like a light switch but it has an overload integrated into the switch.

Front 21

What is direct acting, reverse acting, close on rise, open on rise, and calculate the cut-in and cut-out using a differential pressure switch

Back 21

Know it.

Front 22

What is the setting for O/L on a motor given no 1.15 service factor and 1.0 service factor?

Back 22

sf less than 1.15 will be 1.15 FLA (or sf is not shown)

sf 1.15 equal to or greater will be 1.25 FLA

Front 23

TQ: what is the first thing you do when you show up on a job site?

Back 23

Listen to the customer.

Front 24

What happens if you burn out a heat anticipator on a thermostat?

Back 24

You will not get any heat.

Heat anticipator is a “timed two position control” because the heater is a timer.

Prevents overshoot

Front 25

What position do economizer actuators fail to? Open or closed?

Back 25

Closed

Front 26

With a hot water zone valve is it close-on-rise or open-on-rise?

(The zone valve is fail open, normally open.)

Back 26

Closes-on-rise (24V applied) so the VALVE is reverse acting!

Volts (up) -> temp (down)

However, the thermostat for a zone valve is direct acting. As the temperature goes up the switch closes!

Temp (up) -> volts (up)

Furnace is the direct acting

Volts (up) -> temp (up)

Furnace thermostat is reverse acting

Temp (up) -> volts (down)

Front 27

TQ: Thermocouple open

What effect is it?

Back 27

25mV -30 mV open circuit voltage

Seebeck effect

Front 28

What is “the hop-scotch method” to trouble shooting?

Back 28

Start at power and work your way down, past the fuse, to the damper motor, then the end switch, then the fan interlocks… etc.

Front 29

What do you set up first on a low pressure switch?

What do you set up first on a high pressure switch?

Back 29

Low pressure switch: Cut-in (high event) and then the differential

High pressure switch: Cut-out (high event) then the differential

(High event) - (differential) = (low event)

Front 30

When does the fan limit switch close?

Back 30

Closes at 120-140F

Front 31

Is the heat anticipator in series or parallel for an cooling thermostat?

Back 31

Parallel for cooling, so the heat anticipators heat up the thermostat and will turn on slightly before the room reaches the 20C.

Series for heating, so the heat anticipators heat up the thermostat and will turn off slightly before the room reaches the 20C.

Front 32

Is a condenser fan cycling switch on the high pressure line direct acting or reverse acting?

Back 32

Pressure (up) -> voltage (up)

Direct acting

Front 33

3% voltage unbalance?

How do you calculate it?

Back 33

(Votage (furthest away from average) - Voltage(avg.) ) / voltage average

Front 34

How does a time-guard work?

Back 34

Call -> 15 second delay

Remove call-> 4 min 45 sec delay

Total 5 min

Front 35

Any safety devices are wired before or after the PLC?

Back 35

The safeties are wired directly into the field wiring and not into the PLC program.

Front 36

What does a start top station wiring diagram look like? Pump out? pump down?

Back 36

Blah

Front 37

What does a pump down ladder logic diagram look like?

Back 37

Blah

Front 38

How many times does a pump out circuit?

What does the wiring diagram look like?

Back 38

Once

Front 39

What does the first quiz cover?

Back 39

About 30 Questions

Oil Pressure

TimeGuard Anti Short Cycle

Schematics

Lockout relays

Wiring Diagrams

Electromechanical Controls

Terminology

Transformers

Dampers

Actuators

Flow Switches

Pressure Switches

Thermostats (with and without anticipators)

Humidity Control

Motor Starters

Overloads

Relays

G

Contactors

Design

Gas Fired Equipment

Heatpumps

Maintenance

Front 40

Pump down, pump out, or solenoid drop?

Back 40

Solenoid drop

Thermostat is in front of compressor on a solenoid drop

Front 41

Front (Term)

Back 41

Pump down

Because it pumps down more than once

Front 42

Pump out, pump down, solenoid drop?

Back 42

Pump out

Front 43

A schematic diagram can be refered to as a…..

Back 43

Ladder diagram

Front 44

Pump out, pump down, solenoid drop?

Back 44

Pump out

Front 45

What is the seebeck effect?

Back 45

It is when dissimilar metals produce a voltage. Ala a thermocouple.

Front 46

What is the setting for a low temp cut out on an absorber?

Back 46

34F

Front 47

What kinda questions are on the test?

Back 47

Mostly wiring diagram, or short cycling timer, or pressure control

Front 48

If the lights flash and its 6pm what happens next?

Back 48

The lights will turn off in 10 minutes

If you turn the lights on and off they will stay on for another 2 hours