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Air Con/Heating Fuse D6 Keeps Blowing

logray
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logray Member

logray

Posted
Posted

1999 C2 996 USA.

When I turn the blower fan up past half way the fuse D6 (air conditioning/heating) blows like clockwork. The blower fan stops, but everything else continues to work.

I've got a steady supply of replacement 10 amp fuses to pop in (is it supposed to be a 7.5 amp?), but I don't have a steady supply of patience for problems like this when it is 100 F outside.

Before I start tearing things apart, reading codes and so forth to diagnose an electrical problem or perhaps the failing or clogged blower fan causing excess resistince I searched through the forum and found a couple suggestions like swapping the relay for the blower.

"block 10 the fan, we switch it for the suspect relay in block 18 the blower. (they wre the same types of relays) Like magic the blower fan comes to life!"

Thanks in advance if you've dealt with this before!

rb101 Member

rb101

Posted
Posted

Does blower relay work if you place it in block 10? Fuses blow because the circuit you are protecting is drawing more current then the fuse is rated for. Either you have a bad relay, blower motor, fan resistor, or a short in the wiring.

logray Member

logray

Posted
  • Author
Posted

Thanks, I found out the problem.

I referenced the work shop manual to find out what the proper amperage was and remembered that I was troubleshooting an electrical issue the other day and I mixed up where two fuses went.

I accidentially placed fuse D6 (heater/air con) which is supposed to be 30amp into E7 (air con panel) which is supposed to be 7.5amp (and it actually had a 10 amp in there previously when I bought the car... interesting now that makes me want to go throuh the rest of the fuses and make sure I have the correct amperage at each position).

Put the correct size fuse in each position and it works perfect again.

Thanks!

  • 7 years later...
talkenrain Member

talkenrain

Posted
Posted

I now on the second hottest day of the year am having the same issue. Replace the fuse and the second one piped instantly. I'll pull the relay and check the fan for a short but does anyone have a diagram of what the circuit looks like? Would be very helpful in troubleshooting. Is this fuse only for the fan or does it support other circuits?

  • Admin
Loren Member

Loren

Posted
  • Admin
Posted
18 minutes ago, talkenrain said:

I now on the second hottest day of the year am having the same issue. Replace the fuse and the second one piped instantly. I'll pull the relay and check the fan for a short but does anyone have a diagram of what the circuit looks like? Would be very helpful in troubleshooting. Is this fuse only for the fan or does it support other circuits?

 

Which fuse?

Ahsai Member

Ahsai

Posted
Posted (edited)

If you're talking about D6 (30A), it supplies power (via a relay) to the compressor (via the refrigerant pressure safety switch) and the a/c blower under the dash and nothing else.

Edited by Ahsai
talkenrain Member

talkenrain

Posted
Posted

Ok, thanks. The 30A fuse blew while the air compressor was working. So my new project is to discover if it's the fan motor or the compressor thats shorted. My guess is the fan because I've turned off the compressor from the control unit then replace the fuse but it blew immediately. I'll unplug the compressor and try again to confirm. If you can point me to a wiring diagram, that would be very helpful.

 

talkenrain Member

talkenrain

Posted
Posted

So I removed my fresh air blower. Bench checked it, it checks out fine. I'm going to check the Actuating heat relay and Air conditioning compressor relay tomorrow but I think my problem is somewhere around the 3-level cooling water switch. I don't think it's the air conditioning compressor or relay because I've switched it off and new fuses continues to blow. I tried a new fuse with the blower fan removed from the circuit as well (still blew) So i'm pretty sure I'm tracking down a hard short to ground. I'd be surprised if it's the control unit but I fortunately have a spare to try if needed. 

Ahsai Member

Ahsai

Posted
Posted

You can use a smart fuse (it will blow and light a small LED on the fuse). You can then start disconnect things from that circuit. With some luck the LED goes out and you know that's the bad circuit.

talkenrain Member

talkenrain

Posted
Posted (edited)

Sounds like a great product. I'll try to find one locally. Thanks... although, now that I'm thinking about it I guess I could just use a small 12v bulb across the fuse holder contacts and get the same results.

Edited by talkenrain
Ahsai Member

Ahsai

Posted
Posted
4 minutes ago, talkenrain said:

Sounds like a great product. I'll try to find one locally. Thanks... although, now that I'm thinking about it I guess I could just use a small 12v bulb across the fuse holder contacts and get the same results.

Absolutely. The smart fuse is just more convenient.

talkenrain Member

talkenrain

Posted
Posted

My problem can be marked Solved

I'm not sure if the problem was self inflected since i was just recently in the same area (other side) but looking at the pictures of the relay/DME area of the rear deck on the relay side the chamber that houses all the wires had a few stray wires that where not in the chamber and where squished against the large aluminum panel of the relay circuits. I have a heavy subwoofer that sets on top of this area so I think the weight combined with the heat (over 100 degrees here lately) along with engine/subwoofer vibrations wore away the insulation and shorted against the aluminum panel (ground).

 

The wire being shorted was from the "high/low pressure 3 level cooling water switch" (pin 1). This sources 12v to the air conditioner compressor relay (pin 3, violet/yellow) whenever the ignition is on and cooling water switch is in it's normal closed position. This can all be found in the area of L49 of the wiring diagrams.

 

I insulated the wire, made sure they are all in the wire harness, then remounted the relay panel. Short removed, air conditioner and heater fan are both working properly again.

IMG_9771.jpg

IMG_9772.jpg

IMG_9773.jpg

  • 1 year later...
Mikelly Member

Mikelly

Posted
Posted

SOS... Digging up an old thread.  I replaced my compressor, as it was dying, now the new one is cracking the D6 fuse on my 1999 Carrera. 

Mikelly Member

Mikelly

Posted
Posted

Well as it would happen, I think the compressor was “stuck”.  I jumped it to the power lug and it started working the clutch fan.  Now plugged back into the 30 Amp circuit and it’s working.

  • 5 years later...
ziiz996 Member

ziiz996

Posted
Posted (edited)

Experiencing a fuse D6 meltdown on 2000 CAB 996.   The HVAC blower was working fine the other day, however I noticed and smelled smoke in the fuse box in the driver side footwell to the left of my clutch pedal.  I stopped and turned off the car and found that fuse D6 was melting.  

 Pulled the sticky D6, replaced the fuse and turned off the HVAC system.   Re-Started the car and As soon as I activated the HVAC system, the D6 fuse started overheating immediately ALTHOUGH the HVAC blower was running fine. 

 

So I removed the fuse obviously.  
 

The Car drives fine otherwise; but no HVAC blower I.e No heat or AC.  I live in CT USA.  Very cold now. 
 

I appreciate any Holidays’ Season tips or ideas from our 911 family.  
 

Thank you and Happy Holidays and Cheers All!

 

Edited by ziiz996
Tweaked English
ziiz996 Member

ziiz996

Posted
Posted

Hi Folks,

 

needless to say that the D fuse row needs to be replaced.  It looks very messy.  I also removed the fuses to the left and right of D6.  All other fuse above and below all around D6 were replaced and are working fine.  
 

cheers.  

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