DC - DC converter / AC compressor repair

[Gtech]

Hi guys. I’ve read through this entire thread with interest as my 2017 75D heater has stopped working. Having had big quotes from Tesla I thought I’d have a go myself. The actual heater doesn’t seem too difficult but where on earth do I find this 40A fuse? I think I have a gen 3 DC to DC converter and I can find loads of videos of the gen 1 (wheel arch) removal but absolutely nothing on the Gen 3 one!

Rather than referring to the manual (which I can’t find it in) can someone tell me in plain English (video would be excellent!) where this fuse is located and how I get to it from above (no ramp). I’m pulling my hair out!

Thanks all

This thread will answer your questions, it can be done but it's not a fun job

PTC Heater & FJB extraction from dual motor car

Symptoms: heat no worky. No customer facing errors. Dec 2016 75D Service mode shows two active alerts: THC_w0220_PTC_PtcFault and THC_d0015_cabinPTCHeater HV system diagnostics also show a malfunction in the PTC Heater. My first reaction was to check the fuse for the heater BUT it's...

teslamotorsclub.com

Edit, otherwise follow the PTC HV cable

 

[Tevvy]

Cheers. I’ve found it but there’s absolutely no chance of getting it out from above. I need to invest in a ramp

 

[Gtech]

Cheers. I’ve found it but there’s absolutely no chance of getting it out from above. I need to invest in a ramp

From the bottom there is even less room because the battery is there covering the underside of the FJB and next to that is the driveunit. I would advise to work from above if you do not want to drop the battery

 

[Tevvy]

Yep - you're right Gtech. No access from underneath due to the HV battery.

Whoever designed this is a moron, seriously. There is absolutely no way you can get to the front junction box on a 2017 MS without dropping the battery. From above, the bolts are FACING the firewall and even if I could get to them, there's little chance of reaching the bottom 3.

So a fuse, which Tesla knew was blowing a lot, was MOVED to an inaccessible place. Quite a mistake I'd say.........

Anyone any advice? Other than driving 60 miles to my nearest Tesla Service centre and paying them £££s to replace this fuse (if they'll even do this - probably want to replace the whole junction box).

 

[Gtech]

Yep - you're right Gtech. No access from underneath due to the HV battery.

Whoever designed this is a moron, seriously. There is absolutely no way you can get to the front junction box on a 2017 MS without dropping the battery. From above, the bolts are FACING the firewall and even if I could get to them, there's little chance of reaching the bottom 3.

So a fuse, which Tesla knew was blowing a lot, was MOVED to an inaccessible place. Quite a mistake I'd say.........

Anyone any advice? Other than driving 60 miles to my nearest Tesla Service centre and paying them £££s to replace this fuse (if they'll even do this - probably want to replace the whole junction box).

There is some good advice in that topic I quoted, it's certainly doable but it's a job where you're patience will be tested so no hurry and take your time.

I did not removed the whole FJB just the lid cover. I did removed some of the FJB mounting bolts otherwise there is no room to work

 

[Tevvy]

There is some good advice in that topic I quoted, it's certainly doable but it's a job where you're patience will be tested so no hurry and take your time.

I did not removed the whole FJB just the lid cover. I did removed some of the FJB mounting bolts otherwise there is no room to work

Interesting you were able to do it. I can access one of the mounting bolts from above but there’s 2 on the bottom that I’ve no chance of getting to.

I reckon I might be able to get the cover off with it in place. Like you say it’s a case of taking time and each bolt one by one, but then I won’t be able to see inside it (it’s facing the firewall) but I know where these 2 40A fuses are (fortunately at the top!) but would you know which one is the heater one (left or right when sat in the drivers seat)?

Gonna have a bash at it tomorrow. I can hear the cursing already

 

[Gtech]

Interesting you were able to do it. I can access one of the mounting bolts from above but there’s 2 on the bottom that I’ve no chance of getting to.

I reckon I might be able to get the cover off with it in place. Like you say it’s a case of taking time and each bolt one by one, but then I won’t be able to see inside it (it’s facing the firewall) but I know where these 2 40A fuses are (fortunately at the top!) but would you know which one is the heater one (left or right when sat in the drivers seat)?

Gonna have a bash at it tomorrow. I can hear the cursing already

Once the cover is off I used a small mirror and a light to see where the fuses are, when the HV connectors are off you can measure ohm while they are in place which one is bad.

Sorry, I don't remember which fuse it was. Could help you do it but don't think that driving to NL would be very time/cost effective. Maybe a short vacation? Lol.

Good luck mate.

 

[Tevvy]

Ok guys sorry for the small delay but I’m into the forward junction box now. I can see the fuses with a mirror and have identified with my multimeter on continuity mode that the right hand side fuse is blown (as looking from the front of the car).

BUT, although I’ve disconnected the 12v battery and the first responder loop, I’m *sugar* scared to touch it with my fingers!!

Can anyone confirm or deny (without guessing!) that the thing is safe to touch? I can get my multimeter in but obvs only live in there (where would I put the negative?) so I don’t know what I would be testing to get a voltage reading.

I’m starting to regret getting this far lol

 

[MP3Mike]

Can anyone confirm or deny (without guessing!) that the thing is safe to touch?

The only way to guarantee it is safe is to check it. But with the first responder loop out it should be safe. Even just opening the cover for the junction box should break the HV interlock loop and make it safe.

 

[Tevvy]

Well all’s well that ends well. I’ve changed the fuse and heater is working a treat.

Although the forward junction box now only has 4 of the 8 bolts back in lol.

It’s definitely doable but fiddly as hell to get those bottom bolts from above.

 

[Gtech]

Well all’s well that ends well. I’ve changed the fuse and heater is working a treat.

Although the forward junction box now only has 4 of the 8 bolts back in lol.

It’s definitely doable but fiddly as hell to get those bottom bolts from above.

Great that it's fixed!

For the next time if you want to make 100% sure you have to do the isolation procedure and measure at driveunit or other HV point that comes directly from HV battery:

Vehicle Electrical Isolation Procedure

Theoretical HV is turned 'off' with removing fireman's loop unless a contactor is welded so better measure up front next time and be safe then sorry ;-)

Btw you have a RHD car right? When you are sitting in the car is the front HVJB on the left or the right side? Do you have a picture?

Maybe you can try to put all bolts back since the cover has a lid switch and also to prevent water ingress

 

[Tevvy]

Btw you have a RHD car right? When you are sitting in the car is the front HVJB on the left or the right side?

Apologies I missed this. Yes it’s RHD and when sat in the drivers seat, the junction box is just to the right of centre. Probably above my left foot when driving.

 

[Joni89]

Hi guys. I’ve read through this entire thread with interest as my 2017 75D heater has stopped working. Having had big quotes from Tesla I thought I’d have a go myself. The actual heater doesn’t seem too difficult but where on earth do I find this 40A fuse? I think I have a gen 3 DC to DC converter and I can find loads of videos of the gen 1 (wheel arch) removal but absolutely nothing on the Gen 3 one!

Rather than referring to the manual (which I can’t find it in) can someone tell me in plain English (video would be excellent!) where this fuse is located and how I get to it from above (no ramp). I’m pulling my hair out!

Thanks all

I am having the same issue myself, ended up taking it to a friends local garage after getting quote from Tesla and seeing the videos on youtube seeing how easy it seemed to change myself. Was able to change heater ok issue is changing the fuse in the dc to dc convertor box and no videos on youtube showing how to remove this from the car on the gen 3 models!!!!

What did you end up doing in the end with your one?

 

[Alabaster]

I'm doing this exact job now on my '13 P85. the compressor fuse is blown, but the PTC heater one was ok (replacing both of the 40A fuses while i am in there, along with the 2, 20A fuses).

are any of these fuses directional? Do they have to be installed in a certain direction (suspect not, but never know). If so, how does one differentiate which end goes where? the new fuses i bought from Tesla are SIBA 50 124 34 (blue lettering) whereas the ones i pulled out of hte DCDC converter case were Bussman FWP-40A14fa (red lettering). Before i seal the case back up i wanted to confirm.

 

[mongo]

I'm doing this exact job now on my '13 P85. the compressor fuse is blown, but the PTC heater one was ok (replacing both of the 40A fuses while i am in there, along with the 2, 20A fuses).

are any of these fuses directional? Do they have to be installed in a certain direction (suspect not, but never know). If so, how does one differentiate which end goes where? the new fuses i bought from Tesla are SIBA 50 124 34 (blue lettering) whereas the ones i pulled out of hte DCDC converter case were Bussman FWP-40A14fa (red lettering). Before i seal the case back up i wanted to confirm.

They are not directional.

 

[asavage]

are any of these fuses directional?

See DC - DC converter / AC compressor repair

 

[Alabaster]

Back up and running and I have heat! Seems the bad compressor fuse was to blame. Fingers crossed it holds out. One thing to note for others is the make sure you get the electric cable run for the passenger side marker light installed behind the bolt (there's only one, the other two are nuts) before installing the DCDC unit. I almost didn't and would likely have to take it back off to route the switch cable.

I heard some bubbling and liquid moving around once I got everything out back together. I connected to my mobile charger 110v before driving for a while as I read that can help purge air bubbles from disconnecting the DCDC coolant hoses. I'll have to look up what coolant the car takes to top off the reservoir as it's about 3/8" low (from max).

At a supercharger now seeing how that goes. Started at 44% and slowly climbing at steady 34kW. Does this seem extra slow? There's three other cars so not a large load at the charger stations.

 

[asavage]

Anecdotally, the early MS A/C compressors would overcurrent and cause that fuse to fail; dealerships were replacing the DC-DC first, then months later replacing the DC-DC and the A/C compressor, when the fuse failed again.

If the A/C fuse fails again, you may be in for replacing the A/C compressor as well next time.

 

[Alabaster]

I went into the service mode after the new parts were installed and the eight codes i had before i changed out the fuse is now down to three. That is always a good sign.

is swapping out an A/C compressor something that i can do (or an indie shop) or does it have to be completed at the SC?

 

[Alabaster]

update, after about two weeks, the blower seems to have stopped working. i havent checked the fuses, but i went into service mode and ran the thermal test. the only errors it showed were related to the bumper cover louvers. during the thermal test, i could fee the air get cold and also hot, but the volume of air was similiar to when i initially had this issue.

I don't want to replace the compressor if that is not bad. I heard it engage when running the thermal test (assuming it was the AC compressor). it changed pitch about five times while running the test.

Maybe I just need to take it into the Service Center and see what they find. I thought about doing a total reset of the car system via the computer to see if perhaps that helps. Any thoughts on what to try and diagnose?