Daikin inverter not ramping up

[marc5180]

I've been working on a unit today that has just had a leak fixed, another firm condemmed the compressor and we were called in to give a price.

Ran the system up and the Suction was at 12bar and the Discharge at 16Bar indicating the compressor had ramped right down.

The indoor coil temp was 17-19DegC but the compressor wouldn't speed up.

However when the system was put in test cooling the compressor ramped up brought the Suction pressure down to 8Bar the Discharge stayed at just over16Bar but the air off the indoor came down to 8DegC, as soon as i took off test the cooling stopped and the compressor ramped down.

I'm thinking it must be some sensor (since test run disregards the sensors) causing the compressor to stay at minimum speed but i'm not sure on Daikin what can affect the compressor ramping up.

Does anyone know?

BTW refrigerant is R410a and the charge is correct.


Daikin outdoor RZQ100C7V1B indoor FHQ100BVV1B.

[james10]

is the unit calling for full cooling inside, maybe the air on sensor is not reading correctly check the temp displayed on the controller and actual room temp are you getting a cooling signal from p1-p2 on the outdoor pcb i think it should be 15v dc

[marc5180]

The air on temp is 24DegC, read by setting 41 on the controller.

Not too sure about the cooling signal but i assume i am or the compressor wouldn't be running?

[james10]

Was the inverter board checked/changed
to check the board
inverter diodes MAINS OFF

+J1-P1 0.5VDC +N3-J1 0.5VDC
+J2-P1 0.5VDC +N3-J2 0.5VDC
+J3-P1 0.5VDC +N3-J3 0.5VDC
+P1-J1 OPEN CIRCUIT +J1-N3 OPEN
+P1-J2 OPEN CIRCUIT +J2-N3 OPEN
+P1-J3 OPEN CIRCUIT +J3-N3 OPEN
Inverter transistor check MAINS OFF
+PROBE ON P3-U OPEN CIRCUIT
+PROBE ON P3-V OPEN CIRCUIT
+PROBE ON P3-W OPEN CIRCUIT
+PROBE ON U-P3 0.5VDC
+PROBE ON V-P3 0.5VDC
+PROBE ON W-P3 0.5VDC
U-RED V-WHITE W-BLACK
Both test done using the diode test function a a multi meter

[VRVIII]

I've been working on a unit today that has just had a leak fixed, another firm condemmed the compressor and we were called in to give a price.

Ran the system up and the Suction was at 12bar and the Discharge at 16Bar indicating the compressor had ramped right down.

The indoor coil temp was 17-19DegC but the compressor wouldn't speed up.

However when the system was put in test cooling the compressor ramped up brought the Suction pressure down to 8Bar the Discharge stayed at just over16Bar but the air off the indoor came down to 8DegC, as soon as i took off test the cooling stopped and the compressor ramped down.

I'm thinking it must be some sensor (since test run disregards the sensors) causing the compressor to stay at minimum speed but i'm not sure on Daikin what can affect the compressor ramping up.

Does anyone know?

BTW refrigerant is R410a and the charge is correct.


Daikin outdoor RZQ100C7V1B indoor FHQ100BVV1B.


Hi Marc,

In cooling, the target operation frequency will be determined by the indoor delta t and the evaporating temperature.
Delta t cool = Remote controller set temperature - Indoor return air temperature.
Depending on the cooling load, the target evaporating temperature (Te) will be a value between 2°C & 20°C.
In other words the further the unit is from set point the unit will try to lower evaporating temp to give more capacity.

I would suggest you check the return air thermistor, remote thermistor (if being used), indoor coil sensor, outdoor pressure transducer and possibly outdoor suction thermistor.

Is the unit installed in a low humidity application? Ie. Computer room with constant electrical heat load.

[marc5180]

Hi James10; The system works on Test run function which to me proves that the inverter runs ok, i'll update later today if that is the case.

Hello VRVIII, yes the unit is installed in a comms room. They have temporary cooling in there at the min.
I don't think its due to the low WB temp because the door is constanltly being opened with people going into the comms room.

[marc5180]

Well, i got back to site today and found the unit running with the room temp at 20C with a set point of 20C.

Tested all outdoor/indoor sensors and pressure transducers and all checked out ok,

The suction pressure was around 8bar and the discharge between 17-23 bar with the suction nicely sweating with the compressor ramping up and down.

Bit of a strange one that.

[james10]

I was always told refrigeration was black magic:D

[VRVIII]

Hi James10; The system works on Test run function which to me proves that the inverter runs ok, i'll update later today if that is the case.

Hello VRVIII, yes the unit is installed in a comms room. They have temporary cooling in there at the min.
I don't think its due to the low WB temp because the door is constanltly being opened with people going into the comms room.

Hi Marc,

When installing a RZQ71~140 B or C series unit in a low hunidity application you must programme field setting 16-2-03 (altering target Te & freeze protectection).

Note: This setting will also change the thermostat contol off condition.
Thermo off = Set point -2 C for 5min OR Set point - 4.5 C

When the indoor is operating in low humidity the indoor load decreases which can lead to the coil sensor reading very low temps as EV closes attempting to maintain superheat. This in turn will result in the unit backing off or indoor entering freeze protection.