AC problems, keep blowing fuse #19

jwakil · jwakil's Garage

I've been having intermittent issues with my AC lately, where it will just die (no fan, no nothing), and then comes back on sporadically. Replaced the relay in the smugglers box with no improvement. Thought it was the fan switch, but then I noticed that my fuse #19 was blown. Replaced that but it didn't fix the problem. I noticed it started running again after driving a bit so figured the vibrations affected some loose connection. After it stopped working again I tried to find the loose connection and realized my fuse 19 had blown again! I have a new fan switch on the way, but could there be anything else causing the problem? Based on the diagram below, since fuse 20 is 25Amp, should fuse 19 also be 25A? The one I have on there now is only 8Aamp.

Pazuzu · 12-27-2016, 01:12 PM

Unless you changed the wiring, Fuse 19 does not feed any part of your a/c system, it just shares a +12V feed with fuse 20, which does power your a/c stuff.

Fuse #19 should be a headlight washer system, I don't know if you have that or not.

Now, it's possible that the feed to fuse 19 and 20 is going bad somewhere which might interrupt power to the a/c system and possibly blow fuse #19, but since that same feed goes to fuse 17 and 18, you'd probably know, since fuse 18 feeds (among other things) your CIS OXS computer, and if it was losing power the car would run like absolute crap every time the a/c fans died. I assume you'd notice that...

There is a second round relay in the line of relays in the frunk, not just the cube one in the smugglers box.

What exactly is dying? The evaporator fan, the front condenser fan, the compressor, everything?

jwakil · jwakil's Garage

Quote:

Originally Posted by Pazuzu

Unless you changed the wiring, Fuse 19 does not feed any part of your a/c system, it just shares a +12V feed with fuse 20, which does power your a/c stuff.

Fuse #19 should be a headlight washer system, I don't know if you have that or not.

Now, it's possible that the feed to fuse 19 and 20 is going bad somewhere which might interrupt power to the a/c system and possibly blow fuse #19, but since that same feed goes to fuse 17 and 18, you'd probably know, since fuse 18 feeds (among other things) your CIS OXS computer, and if it was losing power the car would run like absolute crap every time the a/c fans died. I assume you'd notice that...

There is a second round relay in the line of relays in the frunk, not just the cube one in the smugglers box.

What exactly is dying? The evaporator fan, the front condenser fan, the compressor, everything?

Well, everything AC related dies: so no fans, no compressor....but car runs fine.
Based on the diagram, I was assuming that the power to all the AC fans and relays comes from the battery through the fuses 18, 19, 20. Are they in series or parallel? It is very confusing. I do have a headlight washer system, but haven't used it in years. I'm not sure if blowing fuse 19 is related to the AC problem because replacing it doesn't fix the problem, but thought it might be a clue.

RSTarga · 12-27-2016, 04:16 PM

I've got my a/c compressor and fan wired directly to the positive battery terminal, and independently fused.
That is too much load for the fuse box.

86 911 Targa · 04:28 PM

Quote:

Originally Posted by jwakil

Well, everything AC related dies: so no fans, no compressor....but car runs fine.
Based on the diagram, I was assuming that the power to all the AC fans and relays comes from the battery through the fuses 18, 19, 20. Are they in series or parallel? It is very confusing. I do have a headlight washer system, but haven't used it in years. I'm not sure if blowing fuse 19 is related to the AC problem because replacing it doesn't fix the problem, but thought it might be a clue.

For our M/Y 86, the common A/C fuse is #2.

Second from the right on the fuse panel.

As you can see, it does get a bit toasty warm.

^^^^
Here are the two A/C fuse locations.

This one is in the smuggler's box.

Good luck,

Gerry

jwakil · jwakil's Garage

Ok, I do not see a fuse in my mugglers box. I just have a standard relay with 5 wires. I'm assuming the 5 pin relay serves the same function as the 3 pin + fuse shown in Gerry's pic.

I'm going have to be dig deeper. The fuse doesn't explain the intermittent nature of the problem. Will wait for the new switch so I can rule that out.

kuehl · kuehl's Garage

As you can see, the primary AC fuse, which is actually the 2nd from the left on the vehicles fuse panel (ignore the schematic for the moment, look at Gerry's pic) provides power for the:
evaporator blower motor (say 10-15 amps under full load),
front condenser relay ( front condenser fan say 3-5 amps under full load), and
the compressor clutch (say 3 amps max), and
excluding resistance in the circuits overall.
So, the 25 amp AC fuse supports about 16 amps on a good day or 23 amps plus
on a bad day.

The primary AC relay in the smuggler's box originally had an aluminum shell covering it and I believe it may have been a higher amperage, say 20+ amps. This relay is primarily for the Evaporator blower motor. Over time, depending upon the quality of the connections at the relay, resistance in the circuit between the relay and evap motor, and the condition of the evap motor, or its amp draw, these relays can fail. Why they stepped down the relay to 15 amp is beyond me. That is running close to full load.

The front condenser blower relay, as you can see, does not have a fuse before or after.
Porsche added a 7 amp nominal fuse between the relay and the front condenser blower in the very late 80's; there is a factory add on splice kit for this or you can put a 7-10 amp fuse in line yourself (between the motor and the relay).

I've seen plenty of popped or toasted primary AC fuses in various years and its common to see fried red power wire at the fuse. And, in models with electric seats, given the year, a bad seat motor or switch can blow the primary AC fuse.

Have you tested and inspected your front condenser blower motor?

Do you have an amp meter handy you can put inline between the primary AC fuse and other circuits (components) to check your amp loads?

jwakil · jwakil's Garage

Quote:

Originally Posted by kuehl

As you can see, the primary AC fuse, which is actually the 2nd from the left on the vehicles fuse panel (ignore the schematic for the moment, look at Gerry's pic) provides power for the:
evaporator blower motor (say 10-15 amps under full load),
front condenser relay ( front condenser fan say 3-5 amps under full load), and
the compressor clutch (say 3 amps max), and
excluding resistance in the circuits overall.
So, the 25 amp AC fuse supports about 16 amps on a good day or 23 amps plus
on a bad day.

The primary AC relay in the smuggler's box originally had an aluminum shell covering it and I believe it may have been a higher amperage, say 20+ amps. This relay is primarily for the Evaporator blower motor. Over time, depending upon the quality of the connections at the relay, resistance in the circuit between the relay and evap motor, and the condition of the evap motor, or its amp draw, these relays can fail. Why they stepped down the relay to 15 amp is beyond me. That is running close to full load.

The front condenser blower relay, as you can see, does not have a fuse before or after.
Porsche added a 7 amp nominal fuse between the relay and the front condenser blower in the very late 80's; there is a factory add on splice kit for this or you can put a 7-10 amp fuse in line yourself (between the motor and the relay).

I've seen plenty of popped or toasted primary AC fuses in various years and its common to see fried red power wire at the fuse. And, in models with electric seats, given the year, a bad seat motor or switch can blow the primary AC fuse.

Have you tested and inspected your front condenser blower motor?

Do you have an amp meter handy you can put inline between the primary AC fuse and other circuits (components) to check your amp loads?

The PO has put a 7.5A fuse for the front condenser blower. The front blower has been making some rough noises for several years and I have a spare to replace it, but if that blower has failed, would that cause the whole system to die?

My other question is, if fuse #2 is the main fuse for the AC system, why doesn't the factory diagram show that?

kuehl · kuehl's Garage

For the moment, ignore the fuse position in the SC AC schematic and pretend
the 2nd fuse from the windshield is the primary AC fuse.

Glad to hear the front fan is fused.

Take a picture of the first 3 fuses in your car (first three from the windshield) and post it.

There are a few places where you can have an issue turning off the AC,
but let's start at the power source first.

jwakil · jwakil's Garage

See the picture of the first fuses. #4, which is connected to #3 definitely looks corroded. I'm in the process of rigging up a separate inline fuse for the wires of #4 since the screw won't turn and I'm afraid of snapping something off.

kuehl · kuehl's Garage

I'm assuming this fuse panel is in a 81 turbo.

Do you have a schematic of what each fuse is supposed to be for (and their amp rating) , and the 81 wiring schematic at the main fuse panel?

86 911 Targa · 12-30-2016, 06:37 AM

Quote:

Originally Posted by jwakil

See the picture of the first fuses. #4, which is connected to #3 definitely looks corroded. I'm in the process of rigging up a separate inline fuse for the wires of #4 since the screw won't turn and I'm afraid of snapping something off.

pm sent.

jwakil · jwakil's Garage

Ok, looks like the AC wiring diagram is not worth the paper it was printed on. After some research, I found this fuse panel diagram to be closest to what fuse box cover says. So fuse 19 is for the RH parking lights, and sure enough mine are out. Must be some short in that circuit and totally unrelated to the AC problem. Also, after rewiring fuse 4, AC problem still the same. So that brings me back to square. Guess I will just wait for the new blower switch and then take it from there.