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Old 06-24-2013, 10:01 AM   #1
Join Date: Jun 2013
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Dash fuse blows when a/c or heat turned on

I really hope someone can give me some direction on this.

The dash gauges all work fine until I turn on the a/c or heater. Sometimes the fuse blows immediately and other times it may take a few minutes. Even with the compressor disconnected, the dash fuse blows when either are turned on.

Any suggestions on what might be causing this and where I should start?

Thanks, Margaret

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Old 06-25-2013, 09:39 AM   #2

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OK so the common part in the system is the wiring to the blower or the fan that moves the hot or cold air. On the firewall passenger side you should see a bulge which is the blower motor. Single Orange wire connects to it and you have to look down low to find it. Disconnect the wire and see what happens the blower motor could be shorted. Also in the cab passenger side on the f4ront of all the duct work you will find the resistor which gives you your three speed blower. You might want to get VOM Meter and check it for continuity. If it is something else let me know when I get home tonight I can get more info and wiring diagrams.

89 2.5 TBI, 4" RC lift, 1" Booms, SYE, Adams Driveshafts front and rear, Ford 8.8 with 4:88s, BFG 33X12.50X15, and a ton of other stuff.

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Old 06-25-2013, 12:25 PM   #3
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I tested the heater and A/C blower when I bought my 88 (last week), and both worked fine. Yesterday, I turned the vent blower on - and nothing. I checked the A/C, and it's blower works fine.

I have been trying to diagnose the A/C not blowing cold (compressor clutch not activating), so I've been messing with the compressor, but no other wiring (under hood or dash).

If the heater and A/C blower are the same, why would mine work for one and not the other? I don't have complete records on it, so I could have an aftermarket A/C, though.

I'm not trying to hyjack the thread - Just wondering if the blower is truly a common part.
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Old 06-26-2013, 07:31 AM   #4
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I hadn't thought to mention it, but I have an aftermarket A/C unit - hangs on the bottom of the dash and the controls for the heater and the a/c are completely separate. I can actually run both at the same time.

And I just realized that I have been so focused on the dash gauges, that I completely forgot to mention that blowing that fuse also effects the temp of the a/c and it won't blow cold. (not sure it if effects the heater the same way).

Hopefully I can get to my jeep and check a few things out today.
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Old 06-26-2013, 11:39 AM   #5
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From what I've read, even the factory air on the YJ is slung below the dash and has separate controls. That's why adding an aftermarket AC is so easy on Wranglers.

If the A/C won't blow cold, then whatever happens is also effecting the compressor - assuming it blows cold when the fuses are OK. That's what I'm trying to diagnose on mine right now (I hate electrical issues!) - no cold.

I'm still trying to find a good fuse diagram for my 88, but compressors and blowers are rarely on the same fuse since they're both high draw accessories. If they are, however, on the YJ, then Joker's suggestion about a blown compressor is still valid. If not, then it's obviously a short somewhere else.

You can test the blower (if you can get to the wires) by hot wiring it. Don't leave it connected to hot power for more than a second or two, just long enough to see/hear it start. For some reason, devices don't like to take direct battery power (even though you'd think 12V from the battery was the same as 12V through the wiring harness), so only for 1 or 2 seconds!

If the blower starts, then it's something else.
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Old 06-27-2013, 01:55 PM   #6
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On another forum, it was suggested that I check the a/c relay....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. (after looking at the factory manual, it appears that the YJ does NOT have an A/C relay.

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.

(Based on the above, I'm going on the assumption that the compressor is fine.)

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?

HFC3 maybe the 1990 manual will work for you. I'll find the link and post it if you need it.
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Old 06-27-2013, 02:58 PM   #7
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Just ran across the posting where I found the link to the manual I downloaded and low and behold, there's and 87-88 link as well:

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Old 06-28-2013, 09:12 AM   #8
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Thanks for the link. I found an '89 Owner's Manual on eBay, but it would be nice to have a PDF version as well. Oh, wow! the link you provided is the shop manual! Thanks, that was next on the list.

Did you ever say which Wrangler you had? (2.5, 4.0, 4.2)? You mention a 1990?

I've had over-draws before that caused fuses to blow at irregular times. Double check the amp rating on the heater fuse - according to the link above, my 88 is 25amp - the prior owner may have replaced it with a lower rated on that was convenient.

You could try installing a higher amp fuse just to see what happens. This can be dangerous. The amp rating for each fuse is set for a reason. Using a higher amp one will increase the risk of a wire melt down and/or fire. I'd only bump it 5 amp, maybe 10, and only for a day or two at most to see if you get the same behavior. If it stops blowing, they you can decide how to handle it.

From the link above, on the 88 the heater and the a/c are on the same fuse - go figure.

If you can find the manufacturer name, model, and serial number or the after market a/c, maybe you can contact them and get an installation guide for it. You could then compare that with what was really done?

But, looking back, you originally posted this because your dash fuses were blowing, not because your heater and/or a/c weren't working, right? Is this still the case - your dash fuses are blowing, as well as the heater/ac?

Nothing I can see in the link above (at least, for an '88) indicates any shared components between the hvac and the gauges. This leads right back to a short, but not necessarily a short in a blower or other a/c/heater component. Since they don't appear to share anything, it would almost have to be an exposed wire, worn wire insulation, or cross-connected wire.

One off subject questions - where did you disconnect your a/c compressor? Mine appears to be hard wired into the harness.
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Old 06-28-2013, 12:04 PM   #9
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I have a 2.5 94 Wrangler. (I mention the 1990 because that's the manual I've been looking at.) I've had it since 95. If my memory is correct, The same dealership that I purchased it from in 95 had also sold it to the original owner in 94. And I am almost positive that the a/c was installed at that dealership. In looking at the 90 manual for the YJ, it appears that the heater and a/c run off the same fuse for YJs.

What I posted yesterday with all that info, was to kinda get my head straight and make sure that I didn't leave out any details that might be important. But, YES, the dash fuse still goes out. So I need to find where the wiring for the dash and a/c & heater meet up. Just need to decide where to start - don't really want to take the whole dash off if I don't have to.

ANSWER to you question: You should be able to disconnect the compressor at the compressor itself. Check the sides & underneath near the ends of the compressor - you should find a lead wire that connects the the comp.

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