ac fan-fuse 27 pass comp keeps burning out

[david ranger]

Thanks RonD and EricB.
I ran the car for 2 weeks without the AC on, using just the fan.
So with the mode selector switch on the VENT position, 1 click counter clock wise.
Fuse 27 did not blew.

If i put the mode selector switch in any other position and thus activating the AC,
the fuse blows. And he does do that now basically immediately while previously after days or weeks.
And he does it with a hard pitch.

If i run the car without AC so just with the AC the same loud pitch sometimes occurs interruppting the sound of the radio
but without any fuse blowing.

So if I interpret the info you so generously provided correctly,
the short should be in the mode selector switch or in the cable GRY/YEL running from
that switch to the connector C2280B in the SJB and to the blend door actuator.
The actuator which I as advised have disconnected since to rule out that factor.

The other wire BLK/LT GRN could not be the problem as the VENT position is also connected to that
wire and i have no short when running just the fan without the AC.

I know how to measure resistance in the cable.
How to measure the model selector switch itself?

 

[RonD]

So as per wiring diagram, the grey/yellow stripe wire on pin 1 of climate control selector has 12volts with key ON
And if in OFF or VENT the fuse does not blow

When any other position is selected then the Purple(violet) wire on pin 2 gets that 12volts and fuse blows

The purple wire connects to pin 41 on computer

So I would pull out the climate control panel and unplug the wiring connector
Key OFF
test purple wire with OHM meter to ground, 0 to 5 ohms is a short to ground

If shorted then I would pull off the Computers connector, and retest just to make sure its not a computer issue


If purple wire has high ohms or N/C(no connection) then purple wire is OK, problem may be inside the switch itself
Key still OFF
Put connector back on the switch
Put ohm meter on pin 2 purple wire at switch and ground
Cycle switch to see if ohms drop low

There is no Ground on this switch so not sure how it would short

 

[david ranger]

Thanks Ron D.

I pulled out the climate control panel and unplugged the wiring connector.
I measured resistance number 0.00 on both the purple and red wire.
I measured resistance number 1 on the other 2 wires.
The same result with PCM connector disconnected.
I performed all readings with the ground of the battery disconnected and once with it connected
as i do not know if that has an influence. Now i guess not ;-)

So what conclusion can we draw from this? with the below mentioned also taken in mind:

If i put the mode selector switch in any other position and thus activating the AC,
the fuse blows. And he does do that now basically immediately while previously after days or weeks.
And he does it with a hard pitch.

If i run the car without AC the same loud pitch sometimes occurs interruppting the sound of the radio
but without any fuse blowing.

 

[david ranger]

Goodmorning. Anyone can help me out? Kinda stuck..

 

[ericbphoto]

If you got 0 ohms on the purple wire with it disconnected, then its shorted to ground somewhere. It might have rubbed through its insulation somewhere and is touching something.

 

[david ranger]

Thanks.
I checked all of the 4 wires which run almost directly into a big bundle of wires
(taped together by factory) with all the other accessories from the control panel and radio.
No visual damage at all.
It runs up to a T-junction with 1 running left to dashboard and 1 right to the actuator and PCM.
I can see that right part as well and there also no visual damage on the whole bundle.
Everywhere it looks new and its holder clips are also in place.

But I got zero resistance on BOTH the purple and red/orange. Is that correct?

Does it make sense to also test the mode selector although Ron D mentioned to do that
IF the purple wire is OK?

 

[david ranger]

They checked the short of the purple wire again at the workshop with the test light attached to fuse slot 27.
And me under the hood re-and disconnecting the PCM connector at the firewall.
It turns out the short is only there with the PCM computer attached.

We opened it and it looked brandnew. No suspicious looking circuits or foul smell.
As we are on a caribbean island, a new computer is not that cheap.

Could we rule out any other issue or is it 100% the computer?

 

[RonD]

Yes, its possible it's the AC circuit in the PCM that's shorting out.
You could cut the purple wire, where its EASY to splice back together, and then run it that way for a few days to make sure fuse 27 doesn't blow again

You can do a work around to keep AC working without the PCM connected to it

Do you have a V6 engine?
Or a 4cyl with electric cooling fan on radiator

The purple wire at the PCM(pin 41) is the Demand signal for PCM to turn on the AC Compressor

The PCM then GROUNDS the AC clutch relay by connecting PCM(pin 86) black/yellow wire to PCM(pin 69) pink/yellow wire
And IF...............the 2 pressure switches are closed, the AC clutch engages

So you could install your own relay that connects the black/yellow wire and the pink/yellow wire when new relay is activated by the purple wire
This is what is INSIDE the PCM

If you have a 4cyl engine then you would also add the PCM(pin 48) orange/white wire to the same relay connection as the pink/yellow wire, so cooling fan comes on with AC on

You would lose automatic AC OFF if engine was overheating, and AC OFF at WOT(wide open throttle)
AC pressure safety switches would still be working

 

[david ranger]

Thanks Ron D. U r a great help. I have a 6cyl 3.0.

Just for my understanding: Would it be wise to measure resistance in the black/yellow wire and the pink/yellow wire ?
As I understood they are involved in the short in the PCM itself,right?

I will check with the workshop to schedule that work around with that external relay.

 

[RonD]

The Black/yellow wire should be a Ground, 0 ohms to battery negative, key on or off
Its the Ground path thru the 2 pressure switches

The pink/yellow wire should read 12v with key on, 12v from PCM relay, but passing thru the AC Clutch relay's coil
When this wire is Grounded the AC clutch relay activates, and AC compressor starts up

So when Black/yellow wire and Pink/yellow wire are connected together the AC Clutch relay should activate, assuming AC system pressure is OK


The purple wire is just the activation 12v of the PCMs internal "relay" to do this connection, so should NOT be a short to ground, and cause a spike in AMPs that blows a fuse
But this internal "relay" will also have a connection to ECT(engine temp) and TPS(throttle position) to cut off AC Clutch relay's ground when needed

I would cut the purple wire, where it can be spliced as needed, and then run vehicle fo a few days to make sure the fuse doesn't blow

 

[Eddo Rogue]

Does your ac actually work and blow cold air before the fuse blows? I ask because it might be a bad ac compressor/clutch. Mine did the same thing and it was because my ac compressor and/or clutch was seized. I had to repair the ac system and now it blows cold air instead of fuses.

 

[david ranger]

Thanks.
@eric D.
Today i will cut the VIO wire.

After i will put the external 4P relay.
The advised wiring by the workshop was 41(vio) on pin85, BLK/YEL on 86 and 87
and PNK/YEL on 30.
Seems correct,right?

@EDDO
At the workshop they bridged the current at the relay slot in the BJB
and the clutch relay worked correctly.
So that can not be the problem right?

 

[RonD]

......................

After i will put the external 4P relay.
The advised wiring by the workshop was 41(vio) on pin85, BLK/YEL on 86 and 87
and PNK/YEL on 30.
Seems correct,right?

...................................

Yes, that would work

Blk/yel wire should be a Ground if pressure switches are both closed
Vio wire will be 12v when cab switch is on any one of the settings except OFF and VENT

Pnk/yel wire would be a Ground when new relay is activated, 30 and 87 connected

If either pressure switch OPENS then both the new relay and AC Clutch relay would shut off protecting the system

 

[david ranger]

@ericD

I forgot to mention that I actually disconnected the VIO wire completely from the VENT panel switch last week
(it clicks right out if you depress the tab in the connector)
and drove around with no FAN or AC because of it.
No fuse blown ofcourse.
I guess no FAN as the RED/ORG is also connected to the OFF position?

Today I put it back and the fan worked ofcourse again.

I removed all tape from the big bundle leading up to the PCM
to prepare cutting the VIO there and the possible relay installation over there.
Someone was there before as there was some other cabling work done there,btw.
Anyway. my luck, there were 2 VIO cables there.

How to ID which one is which?

 

[RonD]

Unplugging JUST the violet wire on the climate control should not effect the Fan(blower) at all????

Leaving the switch in OFF would turn off fan

The switch has two 12v wires from the same fuse(27 in cab fuse box), one connects to switch with a grey/yellow wire(powers violet wire)
The other connects to switch with a black/light green wire, powers the Fan relay via red/orange wire

Violet wire is on pin 2 and fan power wire on pin 3, so maybe when you unplugged 2, pin 3 got pulled out a bit?



You can use a sewing needle on each of the violet wires to pierce each and test for 12v with switch in AC position(key on) and then in OFF position(no 12v)