1997 Mitsubishi Montero Heater Relay 10amp fuse blows

Tiny
JOESIK@GMAIL.COM
  • MEMBER
  • 1997 MITSUBISHI MONTERO
  • 6 CYL
  • 4WD
  • AUTOMATIC
  • 30,000 MILES
While driving with the heater blower on high it just quit. There are two fuses for it. A 25amp and a 10amp. The 10amp fuse (heater relay) was totally blown and continues to blow immediately upon placing blower swith in the on position. Even with the blower motor wires, resistor wires and the blower motor relay disconected. Tried a new resistor installed, still same problem. What else could be causing the 10amp fuse to blow? I have the schematic if you don't have access.
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Saturday, January 10th, 2009 AT 3:04 PM

8 Replies

Tiny
JAMES W.
  • MEMBER
The 10 amp fuse just powers the coil for the blower relay which is energized when the key is turned to "on". Looking at the diagram, the blower switch should have nothing to do with blowing that fuse. Are you sure the 10A fuse isn't blowing when you turn the ignition to "on", even though the blower switch is off? If I am correct, you have a short between terms 2 & 4 in the blower relay socket. Let me know what you find.
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Saturday, January 10th, 2009 AT 3:49 PM
Tiny
JOESIK@GMAIL.COM
  • MEMBER
I understand and agree with your comments and have blown several fuses to insure that the fuse does not blow until I twist the blower switch to the 1st position. I have turned the ignition on and pulled the fuse to be sure it is not blown. Put it back in and I can hear the fuse blow, soon as I twist the blower switch on. And, again, the blower motor wires and resistor wires are not connected and I have pulled out the blower motor relay. Go Figure? And again, I was just driving on a snow blizzard day, yesterday, with the fan operating on high to keep the windows defrosted. When the blower, just up and quit. My 1st inspection was the fuses, when I found the 10amp heater relay fuse blown. Just to reiterate when the fault happened.
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Saturday, January 10th, 2009 AT 4:01 PM
Tiny
JAMES W.
  • MEMBER
I'm missing something here. If you have the blower motor disconnected, the blower switch and resistor should be totally isolated from the 10 amp fuse. Do you have, or have access to a fax #? If you do, I can ship you a copy of this diagram. I can download to this page, but wiring diagrams don't come through very clearly.
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Saturday, January 10th, 2009 AT 8:29 PM
Tiny
JOESIK@GMAIL.COM
  • MEMBER
I have the manual with the wiring diagarams, but am not good at reading them. Apparently, I've been told numbers on the diagram I am looking at refer to other circuits that tie into that same circuit.I just can't figure out how to jump reference to these other circuits that tie into that 10a fuse.
I do have the blower motor and resistor wires unplugged and the blower motor relay removed.
There has to still be a cicuit on another page where power from that 10a fuse gets effected from the blower motor selector switch, even with the items disconnected above. The very second I twist on the blower selector switch, Bam, goes the fuse.
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Sunday, January 11th, 2009 AT 11:01 AM
Tiny
JOESIK@GMAIL.COM
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Sunday, January 11th, 2009 AT 5:34 PM
Tiny
JAMES W.
  • MEMBER
Looking at the diagram, your AC system runs off the same 10 amp fuse. Under the dash on the right side of the instrument panel is a control module for the AC with an 8 or 9 wire connector plugged into it. Unplug the module and let me know what happens. If it still blows the fuse, your fan switch is shorted to ground inside. Also, how many connectors connect to your blower switch?
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Sunday, January 11th, 2009 AT 7:47 PM
Tiny
JOESIK@GMAIL.COM
  • MEMBER
Appears I found the problem, it was in the blower selector switch. When the selector switch is turned. Inside the switch it creates continuity to both a set of positive terminals and a seperate set of ground/negative terminals. The switch became defective (over 300,000 miles) and apparently, inside the switch it is bringing continuity from the positive connections to the negative and then of course grounding and blowing the 10a fuse. The repair of course is to replace the blower selector switch. Also, for the sake of others in the future, be aware that the same 10a fuse also controls the headlight washer relay and the Rear Defogger relay. Getting to the switch is not easy. First remove the screws that hold the cover plate on the center console and then the screws that hold the complete set of heater controls in place. This was the easy part, but, this heater control unit will not pull out! You have to go to the opposing end of the each of the 3 cable controls and undo each cable up under the dash and unplug each of the 3 electric wire harnesses immediately behind the controls. There is little slack in the wire harnesses and it is tedius, but you can get the wire harnesses removed, but to get to the opposite ends of the cables. You have to remove the lower dash panel on the drivers side to get at the cable on that side and remove the lower duct work cover under the glove box on the passenger side to get at the other 2 cables. When these are all released, now you can cautiously pull the heater controls module outward, I suggest not all the way just about a foot or so, so you don't have to fish all the cables back. In this position you can perform a continuity test on the terminals on the backside of the blower selector switch and AC switch, the continuity diagram is on page 55-5 of the Mitsubushi Montero Manual. To replace the blower selector switch, simply pull on the front knob to remove it and behind it is a plastic nut that holds the switch in, use a 9/16 socket to undo the nut and the switch falls out the backside. I spent days on wild goose chases looking for a short somewhere else, when I wish someone would have said that the blower selector switch actives both positive and negative contacts and that there could be a short in the switch.
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Tuesday, January 13th, 2009 AT 2:53 PM
Tiny
JAMES W.
  • MEMBER
When I first pulled the diagram for your blower system, it showed the AC side of the switch as "not used". It wasn't until I pulled the AC diagram that I saw the system connection.
Thanks for the reply. In our Mitchell reference system there is a section for "tips" and I will post it there. You will have the satisfaction of knowing the entire world will have access to what you have found. Thanks again and I hope we have helped you in some small way.
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Tuesday, January 13th, 2009 AT 3:26 PM

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