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Unread 06-24-2013, 10:36 AM   #1
premjama
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Dash fuse blows when a/c or heat turned on

I've got a 94 YJ. The dash gauges work fine until I turn on the a/c or the heater. Sometimes the fuse blows immediately and other times it takes several minutes. Even with the compressor disconnected the fuse still blows. Would really appreciate some ideas on where the short might be coming from and how I might be able to solve this problem.

Thanks, Margaret

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Unread 06-24-2013, 11:20 AM   #2
pasinbuy
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What size fuse? Have you checked for shorts?
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Unread 06-24-2013, 12:36 PM   #3
premjama
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Fuse is 15 amp.

To be honest, I haven't checked for shorts because other than knowing there is probably a short in the dash, I don't know where to begin. My brother was my go to person for anything auto - especially my jeep, but he passed away a few months ago and my jeep has been sitting at his shop - I had hoped to work on it with him to find the problem, but we didn't get the chance.

I'd like to try and do as much as I can to figure this out without taking it to someone else, but to do that I need some guidance - OK, maybe I'll need a lot of guidance, but I'd like to try.

thanks for responding.
Margaret
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Unread 06-24-2013, 07:26 PM   #4
laybackman
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Quote:
Originally Posted by premjama View Post
I've got a 94 YJ. The dash gauges work fine until I turn on the a/c or the heater. Sometimes the fuse blows immediately and other times it takes several minutes. Even with the compressor disconnected the fuse still blows. Would really appreciate some ideas on where the short might be coming from and how I might be able to solve this problem.

Thanks, Margaret
I think the short is in the dash switch for your heater/ac. Nothing blows until you move that switch.
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Unread 06-24-2013, 07:40 PM   #5
idaholtby
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Fuse F9 (15a), second row from bottom, right most. This fuse has no relation to the heater circuit or the blower motor. I wonder if this could be related to you having this in defrost at the same time. Try removing the A/C relay from the PDC and see if this issue is still present. The A/C circuit will engage whether or not the compressor is plugged in and if the selector is set to defrost, then this to engages this circuit. So remove this relay and see if the fuse still blows.
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Unread 06-25-2013, 08:30 PM   #6
pasinbuy
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I may be wrong but isn't 15a a little low? I would go with a 20a.
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Unread 06-25-2013, 09:02 PM   #7
superj
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What does the book say should be there?
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Unread 06-26-2013, 06:50 AM   #8
premjama
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Book says 15, however, I have used a 20 and 10 and they all blow when ac or heat turned on.

Haven't been able to access my jeep to check the a/c relay, but I hope to today.
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Unread 06-27-2013, 01:05 PM   #9
idaholtby
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Quote:
Originally Posted by premjama View Post
Book says 15, however, I have used a 20 and 10 and they all blow when ac or heat turned on.

Haven't been able to access my jeep to check the a/c relay, but I hope to today.
I strongly advise not to use a higher rated fuse than OEM spec. Many a fire have started this way. I specifically asked if you had the defrost setting selected whenever the heater was activated when the fuse blows. This info would help to discern if it is related to the A/C or not. With defrost, the A/C is still turned on even though it is not asked for specifically even with heat selected or not.
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Unread 06-27-2013, 01:36 PM   #10
premjama
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I did check for the a/c relay, but there isn't one in the PDC. My a/c is aftermarket so how and where everything is connected I guess will take some investigating.

Been looking at a factory manual I found on one of the forums and looking at the diagrams, and I think it's gotten me even more confused and I also realize that I probably left out info in my post that would help so I'm gonna post the facts.

A/C is an aftermarket unit . The A/C controls and Heater controls are completely separate. (I can actually run both at the same time.)
There is no a/c relay in the PDC. Since unit is aftermarket, not sure what relay it's running off. (In looking at the 1990 factory manual, it appears that the YJ doesn't have an a/c relay)

When the A/C or heater are turned on, dash gauges fuse blows (sometimes fuse blows immediately, other times it can be 1 minute or 5 minutes. One day last week, the fuse didn't blow with a/c on even after 10 minutes, then the next day, the fuse blew immediately.)

Prior to the fuse blowing, the a/c will blow nice and cold. Once the fuse blows, it continues to blow, but not cold.
Both the a/c and heater will continue to blow with gauge fuse blown. (not sure if heater continues to blow hot or not)

With compressor disconnected, the fuse still blows.


To get a better idea/understanding of the wiring, Been looking at the factory manual I found on one of the forums for a 1990 Wrangler. The details are different (like position of temp gauge vs oil press., etc.) but I'm guessing the wiring diagram for the instrument panel still serves as a good general guide. Based on the problem I'm having and looking at the instrument panel diagrams, it would seem that the problem is ultimately somewhere within the wiring harness behind the instrument panel?

From reading the info on the a/c system and heating system for the 1990 YJ, it appears that the Only thing the heating system and a/c system have in common is they both connect to the same fuse.

I've been looking at the wiring diagrams trying to get a better understanding of where the common problem might be....I 'think' I'm getting a better understanding, but looking thru the manual as an online doc is confusing. Can't find my hard copy manual, so I may see about getting another.

In the meantime, if I could get some more feedback that would be great. Am I on the right track at all?
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Unread 06-27-2013, 01:49 PM   #11
laybackman
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You must find out where the aftermarket AC unit is getting it's power from.

Most likely from the circuit that keeps blowing!

It should be controlled by a relay if it draws heavy amperage (but nothing would surprise me). The relay is nothing more than a heavy duty switch.

Isolate the power source for this AC unit and your problem should go away.
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Unread 06-27-2013, 02:06 PM   #12
idaholtby
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Quote:
Originally Posted by laybackman View Post
You must find out where the aftermarket AC unit is getting it's power from.

Most likely from the circuit that keeps blowing!

It should be controlled by a relay if it draws heavy amperage (but nothing would surprise me). The relay is nothing more than a heavy duty switch.

Isolate the power source for this AC unit and your problem should go away.
Agree, but I'm still trying to understand the relationship between the Heat and A/C. Defrost setting is the only link I can think of between the two. If defrost is set, and heat is turned on, then so is the A/C. Being this is an aftermarket install, (kind of an important, "oh, by the way") this further complicates things. Perhaps to the point that this is not possible to troubleshoot over the internet without schematics for the aftermarket controls.
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Unread 06-27-2013, 02:12 PM   #13
laybackman
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Quote:
Originally Posted by idaholtby View Post
Agree, but I'm still trying to understand the relationship between the Heat and A/C. Defrost setting is the only link I can think of between the two. If defrost is set, and heat is turned on, then so is the A/C. Being this is an aftermarket install, (kind of an important, "oh, by the way") this further complicates things. Perhaps to the point that this is not possible to troubleshoot over the internet without schematics for the aftermarket controls.
It is how the PO decided to wire this thing up is at the heart of this problem.
He may have gotten 'creative' instead of following the aftermarket AC makers directions which I doubt suggested cutting into another circuit to run this AC unit. Any circuit present has no 'extra' amperage load capabilities due to fuse and wiring sizes.....but I could be wrong!!
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Unread 06-27-2013, 02:28 PM   #14
idaholtby
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Quote:
Originally Posted by laybackman View Post
It is how the PO decided to wire this thing up is at the heart of this problem.
He may have gotten 'creative' instead of following the aftermarket AC makers directions which I doubt suggested cutting into another circuit to run this AC unit. Any circuit present has no 'extra' amperage load capabilities due to fuse and wiring sizes.....but I could be wrong!!
Yeah, it is all a krap shoot at this point. No one really knows except for the original dude that wired this thing together.
To the Op, Try to ID the manufacturer of this aftermarket A/C and see if they have more info that would help out with this.
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Unread 06-27-2013, 02:45 PM   #15
premjama
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Quote:
Originally Posted by idaholtby View Post
I strongly advise not to use a higher rated fuse than OEM spec. Many a fire have started this way. I specifically asked if you had the defrost setting selected whenever the heater was activated when the fuse blows. This info would help to discern if it is related to the A/C or not. With defrost, the A/C is still turned on even though it is not asked for specifically even with heat selected or not.
Starting from the off position, the next position is defrost, then heat, then vent. I usually move the lever to heat but since the defrost setting is before the heat, it usually does engage when going from off to heat.
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