Ferrari 456gta 1996 no power to the ac pump

Sorry, can’t help you with the first two issues, but for the flickering dash lights, try adjusting the dimmer wheel on the dash. That will probably fix the issue.

 

Try percussing the pressure switches on top of the receiver-dryer (dehydrator filter) with the blunt end of a screwdriver. Failing that, you could try swapping out relevant relay (relay B?) on the footpad relay panel with a similar relay. Say, the heated rear window relay? That seems to have the same part number. Check your driver's manual. Sorry, I don't know if the receiver-dryer is accessible on the 456GTA (it's in the right front corner of the engine compartment, just in front of the wheel arch (to the right of the compressor).

In theory, if your pressure switches are kaput, you can short out the pins on the pressure switch plug to earth (as part of faultfinding), but I haven't been able to figure out which switch is which on the receiver-dryer. Possibly a green wire with a black stripe, but if it's a 4 pin plug, you have to know what to do with the other set of contacts (open or short circuit them)

 

By relevant relay, I meant the compressor control relay. Here's the location on a 456M. Perhaps the same as a GTA?

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See also the fuse in that diagram. If you have a blown fuse, however, expect further problems. Do you have fog lights? If so, check that they are working as per the owner's manual.

 

Why didn’t the guy who was going to regas it, diagnose it?
They have trouble with the main control panel in the centre console. It could be almost anything though. A simple bad connection, a relay, a fuse, the pressure switch etc. etc. You need to get a test light and start tracing it.
The suspension problem could also be anything. Have you accessed the suspension control ECU? Perhaps it’s unplugged? If your shocks are buggered, or actuators are stuffed, someone may have disconnected it to stop the warning light coming on.
They aren’t a very complicated system if you know what you are doing (auto Electrician) but if you aren’t, and like to do your own stuff, get a wiring schematic, a good volt meter and an incandescent globe test light and start from the basics. Fuses, relays, triggers.


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That's half the problem ... especially if you live in Kalgoorlie

I pieced together a Frankenstein-type wiring schematic from 456M and 550 wiring diagrams...

Typical HVAC Compressor Control Circuit



It may or may not be correct for the 456GTA. I don't know how power gets to the compressor from the relay panel. Via one of the engine plugs?

 

The minimum pressure switch on the receiver-dryer needs to close when the gas pressure is ok (to allow compressor operation). Would anyone know if the maximum pressure switch on the receiver dryer goes open circuit or closed circuit with too much pressure?

 

You won’t have too much pressure. The pressure required to cut out at high is over 350. Have you got power at the pressure switch?


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I realised that. But the low pressure (or high pressure) switch could be faulty. As part of the faultfinding process, I was wondering if the plug could be removed and the two switches shorted (or one left open circuit) to simulate proper operation of the switches. If you remove the plug, both switches go open circuit. The right signals have to be sent to the relay and the HVAC ECU.

 

The 456M workshop manual describes the switches on the receiver-dryer as having three functions:

minimum system operating pressure 2 bar
maximum system operating pressure 25bar compressor off/20 bar compressor back on
15 bar - right radiator fan on

Not being able to figure out how you get 3 functions from two switches, I chased the wires in the manual coming from the pressure switches:

Switch 1: Right Radiator Fan relay control
NZ (black with purple stripe) wire is an earth.
NV (black with green stripe) wire is the output of the radiator fan fan switch. It's also in parallel with a radiator temperature switch. The temperature and pressure switches send an earth to the Right Fan Relay on the footwell relay panel

Switch 2: Compressor Relay control
VN (green with black stripe) wire sends an earth signal to the HVAC compressor relay when the "min-max" pressure switch is closed
N (black) wire is an earth.

The one (compressor) switch seems to handle all this:

minimum operating pressure 2 bar
maximum operating pressure 25bar compressor off/20 bar compressor back on

So, basically, if you pull off the plug and jumper just the VN and N wires, the compressor should work (if the switch was faulty)

Of course, all this can be thrown away if the GTA is different from the M version.

Diagram updated:

Typical 456? Pressure Switch Circuit

 

Ricambi America is your friend...

https://www.ricambiamerica.com/car-diagrams/ferrari/v12/gt-group-2-2/456gt/electrical-boards.html

Item 24

 

You won’t need to short out any plugs. Just use a test light with an incandescent globe. When you probe the circuit, if it’s a bad pressure switch, the test light will be enough to activate the pump relay. The system is pretty basic, so fault finding is very simple. I’d be surprised if it is a faulty switch though, the HVAC units play up a fair bit. I’ve replaced them in various customers cars. I don’t think they are available new any more, but second hand ones are available. Have you checked all your basics yet?
Start with the fuses. Then check to see if the clutch relay has live at term 30 (battery). 85 and 86 are your relay coil terms and should have ignition on one of them. The other is the neg trigger.


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Adrian, just be aware that if you do go poking around with a test lamp, with the key in ON and put one of the leads of the test lamp on the wrong terminal on the receiver dryer, you may trigger the radiator fan. Watch your fingers.

Jumper leads and test lamps each have their pros and cons. A jumper lead costs next to nothing and you can move away from the engine compartment before applying power. Test lamps confirm power.
To save yourself trying to solder wires onto a 12 volt lamp or lamp holder, you can order a test lamp with a probe and crocodile clip for $10 on eBay, but I don't know how quick the mail is in your part of the world.

https://www.ebay.com.au/itm/12V-Circuit-Tester-Car-Automotive-Light-Probe-Voltage-Pen-Test-Tool-DC-6V-24V-AU/323848107847?_trkparms=ispr%3D1&hash=item4b66d9f747