On a Daikin Applied water source heat pump with the MicroTech III unit controller, three LEDs (yellow, green and red) show the fault or mode. Per Daikin OM 931-7, Table 5: a flashing red LED alone is a compressor high pressure (HP1) fault, a solid red LED alone is a low pressure (LP1) fault, a solid yellow LED alone is a condensate overflow, and a flashing yellow LED alone is a low suction temperature (LT1) fault. All three LEDs on solid means the serial EEPROM is corrupted.
MicroTech III water source heat pump LED table
Read the three LEDs together. The same color means different things depending on whether it is on, off or flashing and what the other two are doing. The LED patterns are Table 5 from OM 931-7; the Type column is added for clarity.
| Description | Type | Yellow | Green | Red |
|---|---|---|---|---|
| Emergency shutdown | Mode | Off | Flash | Off |
| Low voltage brownout | Fault | Off | Flash | Off |
| Compressor #1 high pressure (HP1) | Fault | Off | Off | Flash |
| Compressor #1 low pressure (LP1) | Fault | Off | Off | On |
| Compressor #1 low suction temp (LT1) sensor fail | Fault | Flash | Flash | On |
| Compressor #1 low suction temp (LT1) | Fault | Flash | Off | Off |
| Room temp sensor fail (room sensor control only) | Fault | Flash | Flash | On |
| Condensate overflow (cooling and dehumidification modes only) | Fault | On | Off | Off |
| Low entering water temp (heating compressor inhibit; no display with boilerless electric heat) | Fault | Flash | Off | Flash |
| Serial EEPROM corrupted | Fault | On | On | On |
| Service test mode enabled | Mode | Flash | Flash | Flash |
| Unoccupied | Mode | On | On | Off |
| Occupied, bypass, standby or tenant override | Mode | Off | On | Off |
Two pairs share a pattern in the table as printed. Emergency shutdown and brownout both show yellow off, green flashing, red off. LT1 sensor fail and room temp sensor fail both show yellow flashing, green flashing, red on. When you see one of those patterns, check both conditions.
High pressure (HP1) and low pressure (LP1) faults
OM 931-7 says that if the compressor is running and the high pressure circuit opens, the controller enters a pressure fault mode and the compressor and fan de-energize. For low pressure, the controller enters a fault if the low pressure circuit stays open past a time delay. The default delay is 30 seconds, adjustable if a communication module is present.
Both are latching faults. After the HP or LP circuit closes again, the unit does not return to normal operation until the control board is reset. Clearing the pressure condition alone does not restart the unit.
Low suction temperature (LT1) and Intelligent Reset
In heating mode, the LT1 fault trips when the suction line temperature falls below 28°F on standard equipment, or 6.5°F on geothermal equipment. In cooling mode, the compressor stops and the fan runs for 60 seconds.
In heating and cooling, low temperature faults use Daikin's Intelligent Reset; in dehumidification the fault clears automatically. Intelligent Reset clears the fault automatically the first two times it happens within a 24-hour period and locks the unit out on the third. The retry count resets to zero every 24 hours. A unit that runs, stops and restarts twice in a day and then stays off has likely hit that third occurrence.
Condensate overflow, brownout and sensor faults
- Condensate overflow applies in cooling and dehumidification. The sensor detects high water in the drain pan, the compressor stops, and the controller returns to normal on its own once the level drops.
- Brownout starts when line voltage drops below about 80% of the unit nameplate value. The compressor, pump and fan de-energize, and the unit recovers at about 90% of nameplate.
- Sensor failures do not recover on their own. OM 931-7 lists them as resettable from the network only, not by tenant override.
- Serial EEPROM corrupted does not auto-recover and cannot be reset by tenant override or the network. Because of that, it points at the controller itself.
Units with a second compressor circuit
On two-circuit units, the I/O expansion module handles the second circuit's high pressure, low pressure and low suction temperature conditions in the same way the main board handles the first. OM 931-7 (Table 10) lists the expansion module's patterns: High Pressure #2 is yellow off, green off, red flashing; Low Pressure #2 is yellow off, green off, red on; and Low Suction Temp #2 is yellow flashing, green off, red off.
How to reset a MicroTech III water source heat pump
- Fix the cause first. A reset with the cause still present brings the fault back, and three low temperature faults in 24 hours lock the unit out.
- Use one of the reset methods in OM 931-7. A short interruption of unit power, holding the tenant override button for more than 10 seconds, or a reset from the building automation system.
- Remote reset from the thermostat side. With the cause cleared, energizing the O terminal for 11 seconds or more clears certain high pressure and low temperature lockouts.
- When in doubt, cycle power. The manual notes that cycling unit power always resets any type of fault.
- Wait for the timers. At power-up the controller generates a random start delay of 300 to 360 seconds. The compressor energizes after 45 seconds on a call, and the default minimum off time is 360 seconds. A unit that does nothing for several minutes after a reset may simply be timing out.
Parts involved
| Component | Role in this issue | Where to find it |
|---|---|---|
| MicroTech III WSHP main board | Carries the three status LEDs and handles the first compressor circuit. The EEPROM fault is a controller-level fault. | 668105601 — Control Board Microtech Iii Wshp Main |
| I/O expansion board | Handles the second circuit's high pressure, low pressure and low suction temperature conditions on two-circuit units. | 668105711 — Control Board Microtech Iii Wshp I/O Exp Board-Gold |
| Room sensor | Relevant to the room temp sensor fail pattern on units using room sensor control. | 910171464 — Room Sensor, Microtech Iii |
| BACnet communication module | The manual says the LP delay is adjustable only when a communication module is present. | 668105901 — Control Board Microtech Iii Bacnet Comm Module |
| Pressure switches, LT1 sensor, condensate sensor | These are model-specific. Match them by the unit model and serial number. | Daikin Applied parts |
Scope: This article covers the MicroTech III unit controller for Daikin water source heat pump units as described in Daikin OM 931-7 (August 2019). Other Daikin controllers and older McQuay controls use different indications. The parts above are listed by their live product titles; confirm fit for your unit before ordering.
Before you order
Read the unit model and serial number from the nameplate. Daikin Applied and McQuay part numbers often refer to the same part; see Daikin Applied, McQuay and Daikin-McQuay part numbers. Browse Daikin Applied parts, or contact us at help@totalhvacparts.com with the model and serial number to confirm fit.
Frequently Asked Questions
What does a flashing red light mean on a Daikin water source heat pump?
On the MicroTech III controller, a flashing red LED with yellow and green off is a compressor #1 high pressure (HP1) fault, per Daikin OM 931-7, Table 5. A solid red LED alone is a low pressure (LP1) fault.
What does a solid yellow light mean on a Daikin MicroTech III heat pump?
Solid yellow with green and red off is a condensate overflow fault. It applies in cooling and dehumidification modes, and the unit returns to normal on its own when the drain pan level drops.
Why does my Daikin water source heat pump keep locking out?
In heating and cooling, low temperature faults use Intelligent Reset: the controller clears the fault the first two times within 24 hours and locks out on the third. HP and LP faults latch until the control board is reset.
How do I reset a Daikin MicroTech III water source heat pump?
OM 931-7 lists a short interruption of unit power, holding the tenant override button for more than 10 seconds, a BAS reset, or energizing the O terminal for 11 seconds or more for certain lockouts. Cycling unit power always resets any fault. Clear the cause first.
Sources
- Daikin OM 931-7, MicroTech III Unit Controller for Water Source Heat Pump Units (Table 5 LED indications; HP1, LP1, LT1, condensate, brownout, reset, Intelligent Reset and timers)
- Live product titles for the parts listed above, as shown on each product page
Water source heat pumps involve line voltage, 24 V control circuits, pressurized refrigerant and rotating equipment. Service should be performed only by qualified personnel, following the manufacturer's manual for your unit and your facility's lockout/tagout procedures.