Hello, I have searched through older posts and could not find a decisive answer. On my 550 it seems the A/C must be running to get any warm air in the cabin. I have checked with my hand touching the electrovalve below the dashboard and indeed warm coolant seems to flow through only with the A/C running and gets cold again if I turn A/C off (STOP button pushed in). It makes no sense to me that the temperature control knob should be operative only if the A/C is running, but this makes sense with the owner's manual which says that the electrovalve will be blocked if the A/C is off. Is this all normal?
According to the WSM, that is indeed how it works. Push the STOP button and the whole system is shut down, you only get airflow from outside. Image Unavailable, Please Login
Seems to be a Ferrari "thing"... Same on my F355. I checked it a few weeks ago. Note that it takes a while for the heat to dissipate/build up after pressing the STOP button.
Thanks for the replies... I'd be interested to hear why the guys in the design team validated this solution. I wish them to be deported to cold areas with a broken A/C.
Yes I agree. The reason to shut off the compressor is also to get warm air into the car more quickly. It makes absolutely no sence at all to me that the compressor must run for heat to get out. Wish it was away around this. Any ideas? Manual switch for the compressor clutch?
I assume when you turn off the AC, you lose automatic control of air speed and air direction. One of the features of Ferrari HVAC systems is that it doesn't blow cold air in your face when you first turn on the heater on a cold day (before the engine has warmed up) by controlling the air direction automatically. I don't have an HVAC wiring diagram for the 550 and, strangely, the hot water "proportioning/TGK" valve is not shown in the 456M DIAVIA wiring diagram. I believe the valve is closed when you turn off the AC system (The hot water pump remains running). The valve is controlled by the HVAC/DIAVIA ECU with a pulsed DC signal. You may be able to override it with a switch which applies a constant DC voltage, but it would be full heat with no temperature control.
Thanks for the info! Do you know if there is a kind of manual from the manufacturer of the HVAC system? I guess this is made by bosch or another supplier? There are many "special" functions to optimize the air. But there are some shortcomings too in my opinion. I want to learn how it works. In more detail than the user manual for the car states. all other cars have the option to quite the compressor. During cold winters, it is better to not have the AC running.
Other than the WSM and the Owner's Manual, the only documentation we've been able to find on the DIAVIA system is this: https://www.dropbox.com/t/E0WB4giEqNLqGkIj I've coloured the 456M wiring diagram here: https://www.dropbox.com/t/GKwTUl58CGT0TUHq As mentioned, the wiring diagram is missing the hot water valve. The F355 and F360, F430, etc, wiring diagrams, however, do show the valve.
Does the compressor actually engage or is it just the logic of the system that the Stop button cant be pushed
The STOP button enables the system. The control panel STOP switch sends a signal to the HVAC ECU. I guess the HVAC ECU turns on the compressor via the compressor relay if all is ok. The HVAC ECU sends voltage to the relay coil. Note that on the earth side of the coil, there is also a refrigerant gas pressure switch which is closed if the pressure is between 2 and 25 bar. Here's a shot of the hot water valve on the left hand side of the evaporator unit Image Unavailable, Please Login There seems to be 4 or 5 wires on the connector. If you wanted to bypass the HVAC system, you would need to figure out which are the power wires. I assume some of the wires will be part of a valve position feedback circuit.
The wiring on an F360 hot water valve looks something like this (to be confirmed) Image Unavailable, Please Login The F360 valve connector has a single row of pins, however. The 456M plug looks like 3 x 2? There may be a polarity change on the motor wires to get the valve to open/close. You may not be able to use a simple switch to control the valve.
The compressor's electromagnetic clutch only engages when needed. When the heating is on in winter, the compressor is not running. It is only turned on for a couple of seconds every now and then (30 minutes I think) to keep the system lubricated. Not running the compressor for months wouldn't be good for the system as the gaskets could dry leading to a loss of refrigerant. Stefano
A reason why it is good to have the heat on when AC comprssor is not runbing, is that if you want to switch off the compressor to just have normal air, the windscreen have a tendency to fog up. Then HEAT is a MUST to remove it. Furthermore, the air is dried when the comoressor is running. Good on rainy days, but for very long travels it dries out the air and also my contact lenses. Same in air crafts. It is really really bad on long flights. So I wish I could control the AC. compressor manually.
