Winter Chassis Re-fresh

[Kaz-kzukNA1]

Have you ever noticed the rad fan start operating immediately after turning IGSW in P2 ON position even when the engine is cold?
Both R&L condenser fans and the eng bay fan (if you have one) could be triggered at the same time.

As your issue is intermittent and if not done yet, best re-soldering all of the joints inside the FCU (Fan Control Unit).
Quite a lot to re-solder but still DIY level.

The condenser fans and the compressor CL are controlled separately so even when the former spinning, the latter may not engage.


Inputs to the FCU:
Thermo sensor (mounted on the thermostat cover, different from the temperature sender unit for the temperature gauge or the TW sensor for the ECU)
CCU A/C request
Tripple Press Hi-Lo switch

Output from the FCU:
Rad fan Lo relay control (Low speed mode)
Rad fan Hi relay control (High speed mode, bypass the resistor block)
Eng bay fan relay control (if you have one)
R&L condenser fan relay control
ACS (A/C Switch) signal to ECU

A/C CCU:
Evaporator temperature sensor input
A/C On/Off request to FCU

ECU:
ACC (A/C Clutch) output signal controlling the A/C compressor CL relay.


This is how the A/C compressor CL is controlled.

1. At the CCU, if the Evaporator temperature is above 4degC AND manually or automatically the A/C On is requested, the CCU sends the A/C On request to the FCU.

2. If the Thermo sensor is below 130degC AND the Triple Press Hi-Lo switch is On, the FCU sends ACS request to ECU.

The all of the fans (Rad, R&L condenser, Eng bay ones) are controlled by the Thermo sensor and the A/C On/Off request from the CCU but without the Tripple Press Hi-Lo switch status.

Therefore, if the coolant is extremely hot like above 130degC OR the Tripple Press Hi-Lo switch detects abnormal refrigerant pressure (too high or too low), there is a situation where the CCU is requesting to engage the A/C compressor and while the condenser fans are spinning, the compressor CL won't engage as the FCU doesn't enable the ACS request to the ECU.

3. ECU receives the ACS request from the FCU and enables the A/C compressor CL relay through ACC signal.
At the same time, adjust the engine control based on ACS and Tripple Press MID switch status.


So, multiple controllers and sensors involved.


The outside temperature sensor at the front bumper is not used for the compressor CL control.
If disconnected, the CCU will just use 10degC as the failsafe data and carries on with the rest of the control.


You can force the CCU into the evaporator temperature control mode and send out A/C On request to FCU using the following method.

a. There is no need to start the engine. Just set IGSW into P2 ON position.

b. Press [ AUTO ] dial to power up the CCU if switched off at the last driving cycle.

c. Not required but to save the battery, set fan speed at MIN (1 click from auto mode).

d. Either press on the [ A/C ] switch on the CCU and get [ A/C ON ] on the display or turn the temperature dial all the way counter-clockwise to set it at 18degC.

This will force the CCU into evaporator temperature control mode.
If the evapo sensor is above 4degC, it will send out A/C On request signal to the FCU.


Kaz