Air to Air Heat Pump Systems Troubleshooting

Refrigerant gauges

Digital multi-meter

Step 1. Check ambient temperature.

• With the unit in an idle state for at least 5 minutes, confirm ambient temperature display on control board is close to outdoor temps (within 10 degrees).
• If code is stuck on display, remove Y wire from outdoor unit and cycle power through disconnect. You will now see the outdoor temps on the display.

Results:

• If the ambient temperature on the control board display is not within 10 degrees of the actual ambient temperature, replace the T4 sensor. The part number can be found in the Aftermarket Resource Center.
• If above 125° F in cooling mode, wait until temps go below 125° F.
• If below 15° F in cooling mode, wait until temps gets above 15° F.
• If above 86° F in heating mode, wait until temps drop below 86° F.
• If below -4° F in heating mode, wait until temps raise above -4° F.
• If ambient temperature is between the above values, go to step 2.

Step 2. Checking programming in thermostat.

• Make sure the thermostat is programmed to energize the reversing valve with a call for heat.

Results:

• If the reversing valve is set to energize on cool, have the tech switch to energize on heat.
• If this programming is correct, go to step 3.

Step 3. Check low voltage wiring connected to outdoor unit from thermostat.

• Check voltage from B wire to C wire at outdoor unit.

Results:

• If energized from B to C (18-28 VAC), and trying to cool, remove B wire. Unit will now switch to cooling and a trained professional needs to trace back why it’s getting energized.
• If not energized from B to C (18-28 VAC), and trying to heat, with settings in thermostat confirmed correct, the issue is a bad wire or thermostat and should be replaced.

Digital multi-meter

Digital multi-meter

Digital multi-meter

Digital multi-meter

3 Wire - H,L, Com Troubleshooting

Step 1. Measure Pin resistance

• Power Off unit and wait 3 minutes
• Unplug wire harness and measure resistance between the pins on the fan plug (+/-10%). See wiring diagram for plug location.
  • Pins Black - Yellow/Orange = 40 to 44 OHMS
  • Pins Blue - Yellow/Orange = 90 to 94 OHMS

Results: Do the values match?

• YES - go to Step 2, reconnect the wiring harness and turn power back on.
• NO - Fan motor is out of range and needs to be replaced, the part number is available in the Aftermarket Resource Center. Plug fan motor back in and go to step 2 to confirm correct power from the control board.

Step 2. Measure VAC Voltage

• Give call for heat/cool through the thermostat.
  • Measure the VAC Voltage (Black - Yellow), should read 187-253 VAC
  • Measure the VAC Voltage (Blue - Yellow), should read 187-253 VAC

Results:

• There should only be voltage on one of the pairs, not both.
• If voltages are not in range but ohms are, replace the control board.
• If the voltages are within range but the ohms are not, replace the motor.
• If both voltage and ohms are out of range, replace both the motor and board.
• If all are within range, advise to restart system. If the error comes back, replace the fan motor.
• NOTE: All part number are available in the Aftermarket Resource Center.

3 Wire - W2, U2, V2 Troubleshooting

Step 1. Measure Pin resistance

• Power Off unit and wait 3 minutes
• Unplug wire fan harness (CN32) and measure resistance between the pins on the three silver connectors of the fan plug. Should read 25-40k ohms (+/-10%) across all pairings.

Results: Do the values match?

• YES - go to Step 2, reconnect wiring harness and turn power back on.
• NO - Fan motor is out of range and needs to be replaced, the part number is available in the Aftermarket Resource Center. Plug fan motor back in and go to step 2 to confirm correct power from the control board.

Step 2. Measure AC Voltage

Digital multi-meter

Digital multi-meter

Step 1.

• Check power reading at L1 and L2 using a digital multi-meter (should be between 180-253 VAC).

Results:

• If power is within range and the code has not cleared, replace the control board. The part number can be found in the Aftermarket Resource Center.

Verify incoming power

Digital multi-meter

NOTE: This code will only come up with very early models. Please use the IDS / IDP - E6 Error Code troubleshooting steps.

Refrigerant gauges

Digital multi-meter

S tep 1. Check air filter.

This would be field installed on the indoor unit only. The contractor should be able to locate it. Bosch does not supply any air filters.

• Is air filter clean?

Results:

• If no, replace the air filter and restart the system.
• If yes, continue to step 2.

Step 2. Check service valves.

• Are the service valves fully open?

Results:

• If no, fully open the valves.
• If yes, go to step 3.

Step 3. Checking the outdoor fan motor on the condensing unit.

• Is it running?

Results:

• If no, proceed to test fan (see E6 code).
• If yes, go to step 4.

Step 4. Checking the condensing coil.

• Is the coil clean?

Results:

• If no, clean the outdoor unit.
• If yes, go to step 5.

Step 5. Confirm temperature through the sensors in an idle state.

• Ensure there isn't a call for heat/cool. This can be done either by removing the y wire from the outdoor unit, or just stopping the call from the stat itself
• Go into the parameters menu on the control board and see what the temperature reading is for the T3, T4, and T5 sensors.

Results:

• Compare the temperature readings of the T3, T4, and T5 sensors. Are they all in a similar range?
• If yes, go to step 6.
• If no, replace the sensor that is out of range. The part number is available in our Aftermarket Resource Center.

Step 6: Checking high pressure switch. Use the IDS and IDP Wiring Diagrams for location reference.

• Power down the unit and remove the HPS connection from the board.
• Using a digital multi-meter set for standard ohms, check ohms across the wires.

Results:

• If the ohm reading is OL, equal or greater than 1, replace the high pressure switch. The part number is available in our Aftermarket Resource Center.
• If it is not OL, equal or greater than 1, contact the Bosch technical support specialists.

Digital multi-meter

Step 1. Verify incoming power

• Check power reading at L1 and L2 using a digital multi-meter (should be between 180-253 VAC).

Results:

• If power is within range and the code has note cleared, replace the control board. The part number can be found in the Aftermarket Resource Center.

Refrigerant gauges

Digital multi-meter

Step 1. Checking wiring (with power off)

• Is the pressure transducer (PT) wired correctly?

Results:

• If no, correct the wiring.
• If yes, go to step 2.

Step 2. Checking suction pressure through the parameters menu on the control board and compare to manual gauges.

• Ensure there isn't a call for heat/cool. This can be done either by removing the y wire from the outdoor unit, or just stopping the call from the thermostat itself.
• Is the suction pressure on the field gauges is within 50 PSI (+/- 10%) of check point No. 9/10 (cooling/evaporator pressure) or No.10/12 (heating/condensing pressure)? NOTE: The check point number may be different depending on model. Refer to manual or the back of the cover of the unit for details.

Results:

• If the parameters check points show a 14 or a 505 and its has been confirmed there is a charge in the system; or if the pressure reading of the field gauges is more than 50 PSI (+/- 10%) of the check point reading, the transducer needs to be replaced. The part number can be found in our Aftermarket Resource Center.
• If the parameters check point show something other than a 14 or 505, got to step 3.

Step 3. Checking transducer voltage

• Using a digital multi-meter, check for volts DC from the white to the black wire going to the transducer.

Results:

• If the white to black wire reads 4.9-5.1 VDC, replace the transducer. The part number can be found in our Aftermarket Resource Center.
• If it reads out of that range, contact the Bosch technical support specialists.

Digital multi-meter

Step 1. What error code are you seeing?

• Make note of the error code and go to step 2.

Step 2. Check line voltage

• Check for VAC from L1/L2.

Results:

• Should be between 180-253 VAC
  • If not within range, contact an electrician.
  • If good, go to step 3.

Step 3. Checking system pressure.

• There are two ways to confirm if the system pressure is correct while using the pressure chart found in the manual:
  • Use the parameters menu to check points 9 and 10.
  • Use manual gauges to get the liquid and vapor pressure readings.

Results:

• If pressure readings are not correct, adjust the refrigerant accordingly.
• If pressure readings are correct, go to step 4.

Step 4. Have there been any storms in the area?

• Make note in of any storms in the area recently. Go to step 5.

Step 5. Check for a grounded compressor

• Pull the disconnect at the outdoor unit and let the board power down. Wait 2 minutes to confirm board is de-energized.
• Once de-energized, remove the compressor wires from the board.
• With a digital multi-meter set to Continuity, place one probe on a wire from the compressor and the other probe to a ground connection. Complete this for all three wires from the compressor.

Results:

• If any of the three wires did or did not show continuity to ground, make note of this and go to step 6.

Step 6. Check compressor wires for ohms.

• Using a digital multi-meter set to standard ohms, measure ohms across all three wire connections on the compressor connector: U to V, U to W, W to V.
• Make note of these readings and go to step 7.

Step 7. Checking compressor voltage

• With the compressor still disconnected from the board, turn power back on to the unit.
• Use the thermostat to make a call for heat/cool.
• Once the fan motor starts slowing down, use a digital multi-meter to check voltage across the compressor connection pins on the board: U to V, U to W, W to V.

Results:

• Make note of the voltage readings and contact the Bosch technical support specialists.

Digital multi-meter

Step 1. Check line voltage

• Check for VAC from L1/L2

Results:

• If not between 180-253 VAC, contact an electrician.
• If between 180-253 VAC, go to step 2.

Step 2. Isolating the board from components

• Pull the disconnect and power down the unit. Wait 2 minutes to confirm board is de-energized.
• Remove the compressor, fan motor, crankcase heater and pressure transducer connections from the board.
• Restore power to the unit.

Results:

• Make note if the display does or does not return and contact the Bosch technical support specialists.

Digital multi-meter

Step 1. Is the heat sink and outdoor unit clean? The heat sink is in the unit, behind the control board.

• If no, clean the heat sink and/or outdoor unit.
• If yes, continue to step 2.

Step 2. Checking parameters menu after the unit has been idle for at least 5 minutes.

• With the unit in an idle state, go into the parameters menu and confirm what the Tf and T3 sensor are reporting for temperature.

Results:

• If either sensor is far out of range from the ambient temperature, or showing 32 when it shouldn't, replace the sensor (or control board depending on the age of unit) that has the incorrect reading. The part number can be found in our Aftermarket Resource Center.
• If all of the temperature readings are in a similar range, go to step 3.

Step 3. Confirming fan motor runs

• Start up the unit with a call from the thermostat.

Results:

• If the fan motor does not start, go to the E6 troubleshooting steps.
• If the fan motor does start, contact the Bosch technical support specialists.

Refrigerant gauges

Digital multi-meter

Step 1. Ensure the ambient air temperature around the unit is below 125 degrees F.

• If above 125, it's not an issue with the unit. Wait until the temperature comes down.
• If below, continue to step 2.

Step 2. Is the outdoor unit coil is clean? They can spray it down with a hose or use non-acidic chemicals.

• If no, clean the outdoor unit coil, reset the unit.
• If yes, go to step 2.

Step 3. Is the air filter clean? This would be field installed on the indoor unit only. The contractor should be able to locate it. Bosch does not supply any air filters.

• If no, replace the filter in the indoor unit.
• If yes, go to step 4.

Step 4. Check to see if high pressure switch is open.

• Find the only sensor with 2 yellow wires (labeled has "HPS" on the wiring diagrams). This is the connection for the high pressure switch.
• Using a digital multi-meter set to standard ohms, disconnect the HPS wire connection and put the probes on the pressure switch side of the connection.

Results:

• If not 0 - 0.5 ohms, its a bad high pressure switch. You can recommend the tech jump out the switch to verify. If they do this, make sure they put the switch back in place.
• If 0 - 0.5 ohms, the pressure switch is good, go to step 5.

Step 5. Checking the system pressure

• With the system in an idle state, connect the field gauges to the unit.
• Look in the parameters menu to made sure the board is reading the pressures within 50 psi of the gauges.

Results:

• If the pressure readings are not within 50 PSI of field gauges, replace the pressure transducer. The part number can be found in our Aftermarket Resource Center.
• If the pressure readings are within 50 PSI of field gauges, contact the Bosch technical support specialist.

Refrigerant gauges

Digital multi-meter

Step 1. Verify service valves are fully open.

• If no, have the caller open them and power cycle the unit.
• If yes, go to step 2.

Step 2. Are the indoor and outdoor coils clean?

The air filter on the indoor coil would be field installed and the

contractor should be able to locate it. The outdoor coil can be sprayed clean with a hose or they can use a nonacidic cleaner.

• If no, have the caller clean both indoor and outdoor coils.
• If yes, go to step 3

Step 3. Checking indoor blower.

• Start the unit with a call from the thermostat.
• See if the indoor blower is running.

Results:

• If the motor is not working on the indoor unit and it's a Bosch air handler, contact the Bosch technical support specialists.
• If the motor is not working on the indoor unit and it's a non-Bosch air handler, contact the manufacturer of the indoor unit for troubleshooting assistance.
• If the indoor unit is working, go to step 4.

Step 4. Test pressure transducer.

• Refer to H8 code procedure to test the pressure transducer.

Refrigerant gauges

Digital multi-meter

Step 1. Verify service valves are fully open.

• If no, open them and power cycle the unit.
• If yes, go to step 2.

Step 2. Are the indoor filter and outdoor coil clean?

• If no, replace the indoor filter and/or clean the outdoor coil.
• If yes, go to step 3

Step 3. Make sure the outdoor fan is working.

• If the outdoor fan is not working, go to E6 code procedure.
• If it is working, go to step 4.

Step 4. Check ambient air temperature.

• If air temperature is above 125 degrees, wait for the air to cool down.
• If air temperature is below 125 degrees, contact the Bosch technical support specialists.

Refrigerant gauges

Digital multi-meter

Step 1. Check ambient air temperature.

• If air temperature is above 125 degrees, wait for the air to cool down.
• If air temperature is below 125 degrees, go to step 2.

Step 2. Verify service valves are fully open.

• If no, have the caller open them and power cycle the unit.
• If yes, go to step 23.

Step 3. Are the indoor filter and outdoor coil clean?

• If no, have the caller clean both indoor and outdoor units.
• If yes, go to step 4.

Step 4. Make sure the outdoor and indoor fan are working.

• If the outdoor fan is not working, go to E6 code procedure.
• If indoor fan is not working, check for 240 VAC going into the fan.
  • If no 240 VAC into the fan, transfer to tier 2.
• If it is working, go to step 5.

Step 5. Check the T5 temperature sensor after the unit has been idle for at least 5 minutes.

• Go into the parameters menu and check the temperature reading of "Compressor discharge temp".

Results:

• If the sensor reading is more than 50 degrees away from outdoor temperature, replace the T5 sensor. The part number is available in the Aftermarket Resource Center.
• If the sensor reading is within 50 degrees of the outdoor temperature, contact the Bosch technical support specialists.

Refrigerant gauges

Digital multi-meter

Step 1. Verify service valves are fully open.

• If no, open them and power cycle the unit.
• If yes, go to step 2.

Step 2. Are the outdoor coil and indoor filter clean?

• If no, have both indoor and outdoor units cleaned.
• If yes, go to step 3

Step 3. Make sure the outdoor fan is working.

• Start a call from the thermostat.
• Check to see if the outdoor fan is working.

Results:

• If the outdoor fan doesn't work with a call from the thermostat, go to E6 code procedure.
• If it is working, go to step 4.

Step 4. Check ambient air temperature.

• If air temperature is above 125 degrees, wait for the air to cool down.
• If air temperature is below 125 degrees, go to step 5.

Step 5. Checking parameters menu after the unit has sat idle for at least 5 minutes.

• With the unit in an idle state, go into the parameters menu and confirm what the T3, T4 and T5 sensors are reporting for temperature.

Results:

• If any sensor is far out of range from the ambient temperature, or showing 32 when it shouldn't, replace the sensor that has the incorrect reading. The part number can be found in our Aftermarket Resource Center.
• If all of the temperature readings are in a similar range, go to step 6.

Step 6. Checking system charge

• In the parameters menu, check the "Evaporating pressure" and "Condensing pressure". The exact menu option will vary depending on the model. Consult the owner's manual or the chart on the inside of the control board panel for specifics.

Results:

• If the result is "14" or "505" on any of the checks, use pressure gauges to confirm what the charge in the system is.
  • If the system is low or "flat", find where the leak is and repair.
• If the result is something other than "14" or "505", reference the pressure & temperature chart (field supplied) to compare ambient air temp with system pressure by using pressure gauges to confirm correct charge.
  • If the pressure is more than 100psi off from the chart, the charge needs to be corrected.
• If the system charge is within 100psi of the P&T chart, go to step 7.

Step 7. Checking transducer voltage

• Using a digital multi-meter, check for volts DC from the red to the black wire going to the transducer.

Results:

• If the red to black wire reads 4.9-5.1 VDC, replace the transducer. The part number can be found in our Aftermarket Resource Center.
• If it reads out of that range, contact the Bosch technical support specialists.

Refrigerant gauges

Digital multi-meter

Step 1. Checking the services valves are open.

• If no, open the service valve and power cycle the unit.
• If yes, go to step 2.

Step 2. Checking if the indoor filter and outdoor coil are clean.

• If no, replace the indoor filter and/or clean the outdoor coil.
• If yes, go to step 3.

Step 3. Check if the unit is currently running.

• If the unit is currently running with no issues, it could have been a incidental power supply
• issue. Let the unit continue to run and note any further issues. If the unit is not currently running, there will be an error code. Contact the Bosch technical support specialists.

Digital multi-meter

Step 1. Confirm if high wind area.

• Has there been high winds or a high wind event recently.
  • If no, follow the E6 troubleshooting questions.
  • If yes, wait for winds to die down and see if the code returns.

Refrigerant gauges

Digital multi-meter

Step 1. Verify indoor filter and outdoor coil are clean.

• If no, replace indoor filter and/or clean outdoor coil.
• If yes, go to step 2.

Step 2. Check the T5, T3 and/or T3L temperature sensor.

• After the unit has sat idle for at least 5 minutes, go into the parameters menu and see what the
• reading is for the T3 and/or T3L sensor.

Results:

• If the sensor reading is more than 50 degrees away from outdoor temperature, replace the specific temperature sensor. The part number is available in the Aftermarket Resource Center.
• If the sensor reading within 50 degrees of the outdoor temperature, contact the Bosch technical support specialists.

NOTE: During testing, Motor access panel should be closed.

• Check for 24V between R & C on ECM board.
• Move FAN switch to ON at thermostat. Check for 24V at G & C (should be the same as R & C) terminals on ECM board. If no voltage is present from G to C, please review thermostat or thermostat wires.
• Check High voltage at ECM motor harness circuit. If no voltage is present, ensure that high voltage is present to the unit. For 208/230V at L1 & L2 (black and white wire), for 265/277V at L1 & N (must be within 10%).
• Check 16 pin harness connection and continuity for each wire. If there is any pin that doesn’t have continuity, change the harness.
• On the ECM Interface board set the adjust pin to test while verifying that G to C has 24 volts. If the motor doesn’t start, replace the ECM motor. If the motor starts, replace the ECM Interface Board.