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Installation guides

How to replace a condensing unit

Knowing why a condensing unit no longer works is important because not addressing the root cause of the problem may result in the replacement unit failing as well. This article assumes that the root cause of the condensing unit failure has been identified and corrected and the condensing unit simply needs to be replaced with a new one.

1. Disconnect power
Before starting, be sure to disconnect all power to the unit.

2. Recover refrigerant
Recover the refrigerant in the system using proper field procedures, taking note of the amount of refrigerant recovered.

3. Disconnect service wiring
Disconnect the service wiring: remove the electrical box cover, exposing the relay, and disconnect the wires.

4. Cut the line set and plan placement of new condensing unit
Before removing the existing condensing unit, look at the connections and plan ahead for where the replacement unit will be placed. In some cases, the existing unit has all its electrical connections mounted on one side, while the new unit has its electrical connections mounted on the opposite side. So, when placing the new unit, try to place it so the electrical connections are on the same side as the previous unit. The same holds true for the suction and discharge ports: be aware of where they are on the current unit and try to align the new unit so that the ports are properly located.

Cut the line set following proper field procedures.

Note: it may be possible to loosen the flare nuts and use the existing lines.

5. Remove existing condensing unit
Remove the mounting hardware and the failed condensing unit. If burnout has occurred, a flushing agent should be used following the manufacturer’s guidelines.

6. Install new condensing unit
With the failed condensing unit removed, add the new Danfoss Optyma condensing unit and mounting hardware to the system, including the electrical cover, capacitor, relay, and other hardware. First, put in the mounting grommets, then set the new compressor in place using the mounting hardware. Next add the new capacitor, following the numbered connections to the terminals on the relay in the data sheet, available at odsg.danfoss.com.

7. Prepare copper tubing
Prepare the copper tubing. Wait until after brazing is complete before putting the electrical wires in place to prevent them from accidentally becoming damaged. Dry fit the suction and discharge lines, cleaning and deburring the ends of any copper tubing that will form the new joints.

8. Replace liquid line filter drier
While the system is open, replace the liquid line filter drier.

9. Braze connections
Braze the liquid and suction line connections while purging the system with nitrogen.

Note: do not quench the braze.

10. Test the system
Now that the brazing portion is complete, perform a standing pressure test. It is important to never exceed the system design pressures stated on the nameplate. With the system under pressure, check for leaks using either soap bubbles or an ultrasonic leak detector. Once the system passes the pressure test, release the nitrogen from the system.

Note: never use refrigerant to check for leaks; always use nitrogen.

11. Evacuate the system
Once the nitrogen has been released from the system, pull a vacuum down to 500 microns or less.

12. Connect electrical components
After a vacuum has been pulled down sufficiently on the system, connect the electrical components.

13. Charge the system
Now that the electrical components are connected, we can charge the system with refrigerant according to the manufacturer’s guidelines and reconnect power to the system.

14. Verify system operation
Ensure that the system is operating properly.


Condensing unit installation video

Relay wiring video

How to replace a thermostat with a Danfoss KPU 10

Knowing why a thermostat no longer works is important because not addressing the root cause of the problem may result in the replacement thermostat failing as well. This article assumes that the root cause of the thermostat failure has been identified and corrected and the thermostat simply needs to be replaced with a new one.

1. Disconnect power
Before starting, disconnect all power to the thermostat or the whole system if needed.

2. Remove failed thermostat
Remove the failed thermostat by disconnecting the wires and mounting screws. Then remove the sensing bulb from the bulb strap.

3. Mount new thermostat
First, pass the new wiring through the unit to the back where the new thermostat will be mounted. Pull the wire through the grommet and into the new thermostat. Next place the thermostat in the desired spot and attach with a screw.

4. Connect wiring
With the new thermostat in place, connect the electrical wiring to the terminals.

5. Set cut-in/cut-out
KPU 19 thermostats are flexible enough to either cut in or out on rising temperature. Determine which setting works best for the system and set the thermostat accordingly.

6. Install sensing bulb
Install the sensing bulb, making sure to follow the system manufacturer’s recommendations regarding sensing bulb position. If no recommendations are specified, Danfoss recommends placing the bulb across the airflow of the inlet of the evaporator using a Danfoss bulb strap.

7. Set temperature
Set the temperature. As with any thermostat, use a thermometer to check that the temperature is accurate.

8. Determine differential setting
To determine the differential setting, first calculate the difference between the desired cut-in versus the cut-out temperatures. For instance, if the cut-in is 42 °F and the cut-out is 32 °F, the temperature differential will be 9 °F. Check the table on the back of the cover to determine the differential setting, which in this case will be 4.

9. Set differential
Set the differential using a standard screwdriver, turning the differential adjustment knob to the desired value.

10. Mount adjustment dial or blank-out label
Either mount the adjustment dial, which will allow for easy temperature adjustments, or adhere the blank-out label, which will prevent temperature tampering.

11. Replace cover
Replace the cover, tightening screw to attach.

12. Verify system operation
Ensure that the system operating properly.

Watch the KPU 19 installation video guide

How to replace a thermostat with a Danfoss KPU 60/70

Knowing why a thermostat no longer works is important because not addressing the root cause of the problem may result in the replacement thermostat failing as well. This article assumes that the root cause of the thermostat failure has been identified and corrected and the thermostat simply needs to be replaced with a new one.

1. Disconnect power
Before starting, disconnect all power to the thermostat or the whole system if needed.

2. Remove failed thermostat
Remove the failed thermostat by disconnecting the wires and mounting screws. If the thermostat uses a sensing bulb, remove it now.

3. Mount the new thermostat
First, pass the wires up into the thermostat housing. Next, mount the new Danfoss KPU 60/70 thermostat.

4. Connect wiring
With the new thermostat in place, connect the electrical wiring to the terminals.

5. Set cut-in/cut-out
KPU 60/70 thermostats are flexible enough to either cut in or out on rising temperature. Determine which setting works best for the system and set the thermostat accordingly.

6. Install sensing bulb
Install the sensing bulb, making sure to follow the system manufacturer’s recommendations regarding sensing bulb position. If no recommendations are specified, Danfoss recommends placing the bulb across the airflow of the inlet of the evaporator using a Danfoss bulb strap. 

The next step is to install the sensing bulb, making sure that we follow the system manufacturer’s recommendations regarding sensing blub position.

7. Set temperature
Set the temperature using either the temperature adjustment knob or a screwdriver. As with any thermostat, use a thermometer to check that the temperature is accurate.

8. Determine differential setting
To determine the differential setting, first calculate the difference between the desired cut-in versus the cut-out temperatures. For instance, if the cut-in is 42 °F and the cut-out is 32 °F, the temperature differential will be 9 °F.

9. Set differential
Set the differential using a standard screwdriver.

10. Attach adjustment knob (optional)
If desired, attach the adjustment knob for easy temperature adjustments.

11. Replace cover
Replace the cover, tightening screw to attach.

12. Verify system operation
Ensure that the system is operating properly.

How to replace a light commercial compressor

Knowing why a compressor no longer works is important because not addressing the root cause of the problem may result in the replacement compressor failing as well. This article assumes that the root cause of the compressor failure has been identified and corrected and the compressor simply needs to be replaced with a new one.

1. Disconnect power
Before starting, be sure to disconnect all power to the unit.

2. Recover refrigerant
Recover the refrigerant in the system using proper field procedures, taking note of the amount of refrigerant recovered.

3. Disconnect electrical components
Disconnect the electrical components: remove the cover, slip the spade terminals off the compressor, and finish removing any existing wiring.

4. Cut line set and plan placement of new compressor
Before removing the existing compressor, look at the connections and plan ahead for where the replacement compressor will be placed. In some cases, the existing unit has all its electrical connections mounted on one side, while the new compressor has its electrical connections mounted on the opposite side. So, when placing the new compressor, try to place it so the electrical connections are on the same side as the previous compressor. The same holds true for the suction and discharge ports: be aware of where they are on the current compressor and try to align the new compressor so that the ports are properly located.

Cut the line set for both the suction and discharge sides following proper field procedures.

5. Remove existing compressor
Next, remove the mounting hardware and the failed compressor. If burnout has occurred, a flushing agent should be used following the manufacturer’s guidelines.

6. Install new compressor
With the failed compressor removed, add the new Danfoss light commercial compressor and mounting hardware to the system, including the electrical cover, capacitor, relay, and other hardware. First, put in the mounting grommets, then set the new compressor in place using the mounting hardware. Next add the new capacitor, following the numbered connections to the terminals on the relay in the data sheet, available at odsg.danfoss.com.

The relay should match up and join with the three connectors on the side of the compressor, though in some cases, some additional spade connectors may be needed for the wiring to match up with the new hardware.

7. Prepare copper tubing
Prepare the copper tubing. Wait until after brazing is complete before putting the electrical wires in place to prevent them from accidentally becoming damaged. Dry fit the suction and discharge lines, cleaning and deburring the ends of any copper tubing that will form the new joints.

8. Braze connections
Braze the compressor connections while purging the system with nitrogen.

Note: do not quench the braze.

9. Replace liquid line filter drier
While the system is open, replace the liquid line filter drier.

10. Test system
Now that the brazing portion is complete, perform a standing pressure test. It is important to never exceed the system design pressures stated on the nameplate. With the system under pressure, check for leaks using either soap bubbles or an ultrasonic leak detector. Once the system passes the pressure test, release the nitrogen from the system.

Note: never use refrigerant to check for leaks; always use nitrogen.

11. Evacuate system
Once the nitrogen has been released from the system, pull a vacuum down to 500 microns or lower.

12. Connect electrical components
After a vacuum has been pulled down sufficiently on the system, connect the electrical components.

13. Charge system
Now that the electrical components are connected, charge the system with refrigerant according to the manufacturer’s guidelines and reconnect the power to the system.

14. Verify system operation
Ensure that the system is properly operating.

Watch the light commercial compressor video guide

Watch relay wiring

How to replace a pressure switch with a Danfoss KPU

Knowing why a pressure switch no longer works is important because not addressing the root cause of the problem may result in the replacement thermostat failing as well. This article assumes that the root cause of the switch failure has been identified and corrected and the switch simply needs to be replaced with a new one.

1. Disconnect power
Before starting, disconnect all power to the pressure switch or the whole system if needed.

2. Recover refrigerant
Recover the refrigerant in the system using proper field procedures.

3. Disconnect electrical wiring from the pressure switch terminals
Disconnect the electrical wiring from the pressure switch: remove the cover, unscrew the terminals, and remove the wires.

4. Remove old switch
Remove the pressure connection(s). When removing these connections, use two wrenches to avoid torqueing the copper pipe. Unscrew the flare nut, moving any attached capillary tube(s) up and out of the way. With the pressure and electrical connections detached, remove the old switch.

5. Verify low pressure and high pressure sides for dual pressure switches
Take note of the location of each pressure scale when installing a dual pressure switch, as those made by other manufacturers may differ.

6. Install the new Danfoss KPU pressure switch
Install the new Danfoss KPU pressure switch. If installing a dual pressure switch, the low-pressure side is on the left and the high-pressure side is on the right.

7. Set convertible reset
The Danfoss KPU pressure switch has a convertible reset; it can change from manual to automatic by moving the cam on top. Rotate the cam clockwise to change the setting.

8. Install new pressure switch
If present, carefully bend any attached capillary tube(s) out of the way and mount the pressure switch, either by using the included mounting screws or by using a conduit.

9. Attach electrical wiring
Connect the electrical wires to the appropriate terminal—the number of terminals varies depending on the model. The grounding screw is on the front plate.

10. Connect capillary tubing
Connect the capillary tubing, tighten the fittings with two wrenches to avoid torqueing the copper pipe. When positioning the capillary tubes, avoid placing them where future work may need to be performed and leave enough slack to allow for vibrations without touching other components.

11. Install a new filter drier
Any time a refrigeration system is opened, the filter drier should be replaced.

12. Test the system
Conduct a standing nitrogen pressure test. The standing pressure test should not exceed the maximum system pressure as recommended by the equipment manufacturer. If the system experiences no drop-in pressure, then it is free of leaks.

13. Charge system
Pull a vacuum to 500 microns or below and then properly charge the system according to best field practices.

14. Reconnect power to the unit
Reconnect electric power to the pressure switch.

15. Set cut in/cut out and differential
Set the cut in and/or cut out and differential with the range adjusting screw(s) and the differential adjusting screw, respectively. If installing a dual pressure switch, the high side differential is fixed at 60 psi.

Use either the same settings as the old switch or use the system manufacturer’s recommended settings

16. Use gauges to verify accurate system performance
For the accuracy of the switch, use manifold gauges to verify settings and proper system operation.

Watch the KPU pressure switch video guide

Refrigeration fitters notes

The Fitters Notes provide relevant information about Danfoss refrigeration controls (mechanical) and Danfoss compressors, a good fault location overview, important installation tips and also extra room for own notes. To troubleshoot a specific product in your installation please find a list of relevant troubleshooting documents available for download in the list below the refrigeration overview.

Aftermarket product line

  • Photo of Danfoss appliance controls/universal thermostats
    Appliance controls

    The product range includes among others CFC-free electromechanical thermostats for refrigerators and freezers, produced to precise customer specifications, as well as service thermostats for all refrigeration and freezing applications.

  • The Danfoss series of light commercial compressors with black shells  for commercial refrigeration applications
    Light commercial compressors

    Light commercial reciprocating compressors for low, medium, and high temperatures.

  • The Danfoss line of MTZ/MT/NTZ compressors
    MTZ/MT/NTZ reciprocating compressors

    Maneurop® MT, MTZ, and NTZ hermetic reciprocating compressors by Danfoss are designed for low-, medium-, and high-temperature applications. Compressors are available for a wide range of applications, refrigerants, and operating conditions and future-proven, built-in performance enhancers and safety measures.

  • a blue s-series scroll compressor for air conditioning applications
    S-series compressors

    High reliability, wide application envelope, and easy manifolding.

  • Danfoss DSH compressors with IDV techology
    DSH-series scroll compressors with IDV

    Optimal performance under part-load conditions

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