Is there away to test the functionality of the 355 HVAC control panel? I have done all the usual stuff for the HVAC repair including the ECU repair (twice). Now I have all kinds of issues. No AC engagement with the heat control on blue dot...system engaged No heater engagement with heat control on red dot. ..system engaged The fan controller is working but clearly on the wrong scale. The air distribution function is not working despite tests on the controller being positive Same for re-circ flap. My suspicions are starting to point to the HVAC panel not providing the proper outputs. Is there a way to test the outputs of that panel?
Some of them at least. The internal components are simple enough (apart from the blue "PPTC" (polymeric positive temperature coefficient"). Just resistors, diodes, switches and lightbulbs, but you'd have to pull most of them out of the circuit to check them. Probably best to feed the panel 12 volts and an earth on the bench and check the voltage outputs. I don't know all the functions of the pins on the panel. Here are some of them at least: There are lots of threads on HVAC panels on the forum... too many to sort through... Here's one https://www.ferrarichat.com/forum/posts/146337695/ Someone found a damaged track on the board (but that was a lighting-related problem)
Thanks...as always. Chasing this seems more complicated than I expected. Yea, aware of the other threads, but this is very specific to the HVAC panel.
I had similar issues and ended up with a spare HVAC panel that I got in a package with a rebuilt ECU. I know how frustrating this testing loop can be. I can make it available for troubleshooting; shoot me a PM.
I may some not so technical feedback to offer.. I've had a similar issue.. but somewhat figured it out.. I have owned my 1997 GTB nearly 8 years.. and in the fall/colder months of the driving season.. my car has always provided perfect heat on demand.. haven't been getting cold air for a few years, needs to be recharged.. so really in the fall months, was the only time I would engage the compressor to get heat.. otherwise the compressor button is always off/pushed in. on a fall drive last year.. colder out, I engaged the compressor (button out), and temp to full heat. car was already well into full operating temp.. driving, driving, driving.. zero heat was coming out.. as is my nature, I went into complete OCD mode.. turning the dials back and forth.. AC button in/out a dozen times.. Nothing! even though I had not been getting cold air for several years.. the heat worked perfect all the time.. when needed. so this was the first time noticing this issue. finally when stationary at idle.. in my driveway.. still trying to figure it out to get heat.. loosing my mind.. I wiggled the AC button, while it was in engaged/out position.. it has a bit of play to wiggle it side to side.. boom, I immediately heard the compressor "click" sound.. and heat started to flow..! so in my case.. the fault seems to be the actual compressor button..and with almost perfect repetition, if needed heat, would do the same.. and it worked.. I went as far as removing the unit and opened it. and under the AC button, there is a rod thing that comes up from the mother board.. so it seems to be an issue related to contact, when the button is out.. it is not engaging the compressor and by wiggling it.. allows whatever contact or un contact to occur, to get the compressor engaged. so in short, this is my not so technical solution.. would like to get this looked/corrected.. next time I get the car to my mechanic.. if perhaps theres a way to adjust the spring or whatever under the button.. so that the out/on position of the button provides the correct signal to the mother board.
The PCB is very fragile and low quality, i know as I repaired and resoldered mine. Surprised no one has cloned the PCB as it consists of very simple components....
OK, a certain someone who shall not be named loaned me an HVAC panel. My problem remains. In poking around at this, I don't seem to have power to fuse #24 which, I think, powers the panel. Looking at Fig 6 in @Qavion diagrams I can not see where the power comes from. It just shows splice 30020. Any guidance?
Not sure if you have my latest 5.2 diagram, but the HVAC ECU is powered by fuse 24. The HVAC panel is powered by fuse 26. Oddly, this also powers the brake lights and windscreen wipers. See splice 30046 https://www.dropbox.com/t/mYXbzzCsl0mokb9E Are these working?
Thanks! Windscreen wipers work as do the brake lights,. Interesting fact, if the brake lights do not work, you can not select first gear in an F1 car at stand still. Oddly, the power mirrors do not work. I should show 12 volts at the use box for fuse 24. I have nothing.
Weird. Is this with the ignition on? Are the plugs on the HVAC panel and mirror control panel identical? Have you swapped them around by mistake? (Disregard... I see one has 7 pins, the other 8)
Ignition on. Engine running. Plugs are not interchangeable. Tested a second HVAC panel thanks to Dave Rocks. I have no power to fuse 24...... Where is splice 30020?
By "no power to fuse 24", you mean you've checked power at the fuse with a voltmeter? If you have no power to fuse 24 (and you've changed the fuse) then it has to be an internal relay panel problem. If you have no power at fuse 24, then there is no point looking for splices downstream of the fuse. Are you using your owners manual to identify the fuses? The WSM only shows the 2.7 car numbering.
Yes, checked for power at fuse 24 with the fuse out. Nothing there. Fuse in. Nothing there. With a voltmeter and my handy dandy old school 12 volt pick light. Good point on the splice question... I need to find the upstream power feed to fuse 24. I have a 5.2 car
The power for fuse 24 comes into the relay panel on two wires from the ignition key. I think you'd have a lot more problems if these failed. I can only think that the fuseholder mounting pins have detached from the relay panel internal fuseboard. Any signs of fuseholder melting?
Thanks and agree. Car runs fine. Everything else works save for the mirrors. But no juice at fuse 24. What relay panel? The one in the footwell area? Is there a relay that feeds that fuse? I don't see it, but maybe I missed it?
Yes. No relay. It's all hardwiring (inside the panel). The ignition key feeds power to the relay panel. The relay panel internal printed circuit board distributes ignition key power to the applicable fuses and relays. Image Unavailable, Please Login (Sorry, don't know whose photo I stole here) Mirrors run on the same fuse as window heat (probably hard to check in summer). On some later model cars, the cigarette lighter also. These are affected by relay P. Relay P is powered with the key ON, but is de-energised temporarily during engine cranking. Relay P also powers the HVAC control panel. Unfortunately, this doesn't help with your fuse 24 power.
I show relay P as the LH fuel pump. But I assume that's for a 1995 car.... Obviously not applicable to my 1998 car. I'll pull and check Relay P next. Think the fuse box lost connections?
Hence my earlier comment on checking your 5.2 handbook and not relying on the WSM. Is fuse 24 really fuse 24?
Here's my 5.2 (gated) handbook pic Image Unavailable, Please Login I'm not sure if there are any F1 variations (for those with F1 cars)
I hear you. Fuse 24.... row 2 #4 in the footwell fuse / relay block In your pic fuse 23 I have an F1 car....
I would have called it row 3 (even though there are no fuses in row 1) Anyway, 3 fuses to the left of relay "O" in my pic (above)
Hummm. fuse 23...and I'll check relay "O". Too many moving pieces. Thank you for the help......learning.....
I think I've confused you... or vice versa. Where did you get fuse 23 and relay "O" from? You need to check the fuse marked below (for HVAC ECU power). I just remembered that this is also the instrument panel power fuse, so I'm sure it's ok if your speedo/tacho/etc is working. Image Unavailable, Please Login Note that fuses and relays in the same locations have the same functions on 2.7 and 5.2 cars (generally). The manuals just number them differently. I just mentioned relay "O" as a position reference. It has nothing to do with your car's problems. (EDIT: which fuse in the diagram above were saying was fuse "24"?) Maybe you could post a picture of the decal on your relay panel coverplate?
We are on the same page then. Fuse 24 is my concern. I have no power to the fuse. Ignition on or off.
