348 HVAC heat constantly on

This issue started intermittently maybe two-three weeks ago whereas after warming up the car from a cold start I would get on my way and warm air (pushed normally through by the car motion) instead of ambient air would come out of the vents without the HVAC panel being activated.

The first time this happened and subsequently another 2-3 times after that I turned on the A/C for a few minutes, cold air came out as expected, and after turning it off the ambient air temperature coming through the vents was restored.

This happened again today with the only difference that turning on the A/C did not produce any cold air at all. Note that the A/C/ is fully operational, was serviced recently during the last major, and never showed any signs of malfunctioning in the past. So this issue has now gone from intermittent to constant. I am no car-repair genius but I have the sense this is an electrical thing.

As another data point the HVAC panel is behaving normally, with each function producing the expected behavior. In past threads about misbehaving HVAC I read about the infamous "bullet-type fuse" and how it almost invariably causes issues: could this be related or am I barking up the wrong tree? Should I look for other possible culprits?

Last thing: either way, once I remove the front boot liner I am going to replace the "bullet-type fuse": where can I find a suitable replacement?

 

ebay basically, any car audio reseller on there has them, 30 amp glass bullet fuse. I crimped ferrules with ferrule crimp on the wire ends and then put those into the fuse ends.

 

Things break.

Can you hear/feel the AC compressor clutch kicking in when you turn on the AC? (engine running). Does the engine rpm change slightly?

Low AC gas pressure will disable the compressor. If the compressor is not turning on, maybe you have a leak somewhere. Service ports are known to leak if you don't put new valves/seals in.

If the compressor is not turning on, but the blower fan is still running normally (at all speeds), then it's probably not a power issue (i.e. not the big fuse or fuse 6 in the footwell).

The HVAC ECU controls the compressor via the compressor relay in the frunk. The relay coil uses power from fuse 6. Fuse 6 also powers the little suction motor for the inside temperature sensor. Can you hear that running? Fuse 6 also powers the hot water pump. With the engine warm, do you get hot air?

Power from the compressor relay goes to one of the gas pressure switches on the receiver dryer and then on to the compressor clutch. If the gas is low or the pressure switch is faulty, in theory, you can jumper the switch, but I'd only do it momentarily to see if the compressor activates. Jumper the green and green/black wires on the plug going to the switch.

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In theory, you could also jumper the relay to see if it is a relay or HVAC ECU issue. i.e. pins 30 and 87. If the compressor starts, you know you have power, proper gas pressure and the HVAC ECU is operating normally.

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Is the condensor fan at the front of the car running? Are the gases being cooled?

I suppose another possible issue might be faulty temperature sensors.

One step at a time. The experts will tell you what is most likely to break.

 

Thank you for the replies.

So this afternoon I removed the frunk liner and started poking around. I carefully checked all relays/fuses and didn't find any evidence of melted seats. Even the infamous 30 amp fuse that is often replaced with the glass bullet-style is looking perfectly fine. Again the HVAC control panel appears to be working well, showing no codes, etc.

I then turned my attention to the heater control valve (#8 in the diagram below)

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I noticed the "dial indicator" where the pencil is pointing in the image below (I borrowed this pic from another thread) was turned to "fully open". I reseated and used contact cleaner on as many connectors as I could get to. I then ran a test by turning the car on, letting it warm up and simply turning on the fan on "ambient air" setting to check the air temperature coming out of the vents. As soon as I turned on the car the "dial indicator" rotated to "fully closed" and the air coming out of the vents stayed at ambient temperature for the duration of the test. Similarly, I activated the A/C, it made all the noises that are expected, the compressor started, the engine idle dropped a little, and cold air started coming out of the vents.

At this point it seems to me the heater control valve was stuck on "open" - which is probably why the A/C couldn't properly kick in (?)

Was I able to correct it just by using contact cleaner? Or is this just an intermittent problem and I simply got lucky twice in a row but maybe next time I go for a drive the same issue will reoccur? I don't know but I ran another test by turning on the car and going through a similar procedure later in the afternoon with the same positive results.

I will update this thread as I accumulate more data points: I drive the 348 frequently so I expect to be able to post an update in the next few days. Meanwhile please keep your troubleshooting tips coming!

 

I don't know if this is some kind of default position (?). I know on the 355 if you hit the AC STOP button, the valve closes (not opens). I seem to recall a spring on the valve (?). Is it powerful enough to drive the valve open (against the stepper motor)? Unfortunately, all this stuff is hidden from view and not easy to check.

Hard to say.

The HVAC system may be like the F355's with an ECU driver chip dedicated to the valve. The chips are known to fail. Maybe try switching from hot to cold a few times to see if you can reproduce the problem?

 

This is what I did when I had this common HVAC 348 problem.

I bypassed the heater hoses so the heater never turns on. The AC works as expected. Living in California, AC is more important. You have to pick your poison.

 

I hear ya. But I am a bit of a stickler for originality: if it was meant to be working a certain way from the factory I'll make sure it works as it was intended.

 

Same issue here. I cleaned the heater

Do you have any suggestion with is new found issue? The relay next to my 30 amp seems to be failing fast. I'm about to install a bullet 30amp, but then found this replay melting. The part number for the relay is 63306800 , but I'm not sure it is in stock anywhere. Is the base of the damaged relay standard because I'm not finding a part number.

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Hi, had a melted 30amp fuse holder last summer in my F355, that was caused by excessive power consumption from the ac compressor clutch coil. So that might also cause your problem with the melted connector for the relay since it’s supplied from the same circuit. The measured resistance between coil and ground should read 2,8-3,3 ohm if you disconnect it and measure.

I have also experienced the HVAC ecu output op-amps to fail as mensioned above. These controls the heating valve stepper motor among other valves in the system and they seems prone to fail.
I’ve bought new and plan to get a specialist shop to install them..
these: https://www.ebay.com/itm/255838422717

 

Ironically your hidden fuse looks in good shape. I'm not sure what the relay is for, be interisting to know, I assume ac in some form since it's tied in. That may be your issue.

 

Going by the wire colours, it's definitely the blower fan relay, but the large light brown/orangey wire going to pin 30 of the relay carries power for the blower fan regulator and the AC compressor clutch. The relay base (pin 30) also carries power for the ECU (i.e. live battery power)

See relay (68) in the diagram:

https://www.dropbox.com/t/Gx0rpHlbs83HHh2m

This is bad news. Even if we change the fuse to a bullet fuse, it just moves the problem to the next weakest link.

 

Are the relay switch seats standard for most relays? I found some bosch style relay seats that look the same. Clearly I need to replace this part. Thank you so much for the diagram. I hope I wont need it too often.

 

They look like standard Bosch relay sockets.

Does the graphic on top of the relay case show any resistors or diodes across the pins?

There have been frequent discussions on the 360/430 and 575 forums about the high powered F1 pump relays. Perhaps one of these would be a good substitute for the green relays. I guess it depends on the rating of the green relays. 30 amps or are they higher?

BMW/Tyco F1 relay subsitute for OEM:

https://www.ferrarichat.com/forum/posts/149231001/

 

The two relays at the hidden fuse are same and they are standard 4-pin relays, nothing special. You can also use standard 5-pin relays which have "87 87" shown on their diagram but the 5th pin, positioned in the centre, will not be used.

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The relays and the hidden fuse:

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Since there are no signs of burning/melting at your fuse, I don't think you have any overload. The burning at the relay is probably due to developed resistance at the pins/sockets caused by corrosion (moisture in the boot). It is a good practice to, say every one or two years, remove each relay and inspect/clean its pins. This is especially important for the relays that carry high current like the two relays at the hidden fuse and the relays for the radiator fans, fuel pumps and injection. Same applies to the fuses.

 

UPDATE on original problem: after cleaning the contacts on the water heater valve and elsewhere in the same system (as I described above) I drove the 348 twice in the past few days and each time the HVAC behaved as it should have. No hot air out of the vents when none was requested and the A/C is working as it should.

It may be too early to declare victory but for now it is safe to say that owners experiencing the same issue should at least try this same easy approach instead of jumping headlong and start replacing parts. So far it seems to be working.

I'll update this thread again as I drive the car.

 

Glad it worked for you as well. I also try to apply Stabilant 22 to any electrical contacts that accessible while I stooge around on the F-Car.

I just replaced the melted solenoid sockets 68 and 67 along with 30 amp fuse. All went well and is working fine. Standard NAPA AR419 is what I could get my hands on. I'll report back if anything fails.
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UPDATE #2: took the car out again today and the HVAC showed no problems. No warm air when only ambient air was selected. Maybe I did get lucky and solved the problem by simply cleaning as many electrical contacts/connectors in the HVAC system as I could get my hands on.

At this point I won't annoy anyone with further updates if the original problem no longer occurs. I will, however, come back to this thread if the same issues come back.

 

Follow up (four months later!).

The HVAC system was mostly behaving normally since my "procedure" - see above - when a few days ago suddenly the E8 code popped up on the panel while in Heat mode. Nonetheless, it was still blowing warm air. A few restarts eventually removed the code, which came back on one occasion but overall all went well from there. It all seemed to happen without rhyme or reason but hey, it's a Ferrari.

The very same day, later in the drive I started experiencing odd electrical issues in the cabin: the dome light was dimming but not turning off altogether even when the doors were shut... lowering the driver's window would activate the seatbelt buzzer, dome light and brake light in the cluster (!)... door lock buttons were inoperative, and other similar odd behavior. I knew right away that the culprit was likely the driver's round door connector and, sure enough, once I got home and took a close look as many as six wires had become disconnected from their pins. SIX! I had fixed the occasional pin in the round connector before but this was Armageddon.

What a great opportunity for a straight-wire project. Armed with patience, a bucket of butt crimp connectors, and some 14 and 18 gauge wire I chopped off all the pins and tackled the beast. Those of you who have completed this task before me know it isn't fun but at the same time it isn't exactly hard to do: it does however require a fair amount of patience and attention to detail. To make a long story short all is working well again and I don't expect to ever have to deal with this issue again.

One item of note, and the main reason I am adding this post to this specific thread is that the E8 code as well as any sporadic and inexplicable behavior from the HVAC system have now disappeared. It is indeed quite odd the the E8 code appeared minutes before I realized about the cabin electrical issues. Similarly, as I suspect the round connector wires didn't become dislodged suddenly but over the course of time, I am inclined to believe there is some sort of association between the connector issues and the odd HVAC behaviour I witnessed in the past few months.

Moral of the story: if you are having issues with your HVAC it would be a good idea to also check your driver door round connector wiring. Based on my experience, the two systems may be more closely related than it seems.

 

A very tenuous link I think. I couldn't find any common power connection between components in the doors and the HVAC system (other than the battery/alternator/ignition key). On the F355, the outside air temperature sensor is on the driver's mirror, but not on the 348.

 

TUV regulations require a default to full heat and open defrost ducts if the system has a failure.

 

Agreed. What makes me think there are unknown connections between seemingly separate systems is also the fact that while activating the driver's door window switch the brake light in the cluster would come on and then go off as the switch was released. Odd beyond measure.

 

E8 is related to "electric water pump for heating". If that thing seizes it has been known to burn out parts on the hvac board. I replaced my heat pump for good measure I doubt they are designed to last 30 year's.

 

Crazy design. Why they wired that to the ECU I don't know. Same on the F355. On the 360/F430, the pump is completely independent of the ECU, and runs whenever the ignition is on. Not that that is a good design, either.