Another HVAC Blower Issue - Solved?

[98TxTJ]

I have a 1998 TJ Sport, 4.0 5-speed, purchased a few weeks ago. The HVAC blower fan was not working when I bought it. By not working, I mean nothing. No fan regardless of any switch or control settings.

I read lots of threads on fixing similar problems and replaced the fan switch, the resistor pack, the blower motor with no change in the symptoms.

This is the old style slide control panel, not the newer panel with multiple knobs.

Today a friend and I went through the schematics and systematically tracked power through the circuit. We had good power and connections everywhere.

No melted connectors were found anywhere. We interchanged old and new components without any change in results.

We had 12+ volts at the connection for the blower motor, but the motor wouldn't turn. Both blowers worked fine direct-connected to the battery terminals.
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As a hail-Mary final play, we connected one of the blowers to the positive side of the connector at the firewall and ran the negative from the motor to the negative battery terminal. It worked! And all the controls worked too!

Clearly there was something in the ground circuit that was not passing enough current to run the fan.

We cut the black wire that goes to the blower motor from the relay and resistor and connected it directly to a ground point.

Everything now works exactly as it should.

The question is, what and where is the ground problem that we bypassed?

 

[Chris]

I wish I could answer your question, as I'm not sure what ground it would be. You'd have to likely tear apart the dash and look for the ground, or see if you can find it in the wiring schematics.

Very funny, because almost the exact same thing happened to my old 2000 XJ I used to own. Literally the same exact symptoms. I tried everything you did and eventually broke out the wiring diagrams and multimeter and started tracing power all the way in from the battery, to the control panel itself.

I found that part of the power wire had power coming through the fire wall, up until the junction box under the dash. At the other side of the junction box, there was no power coming out of that wire at all. It ended up being a loose / faulty connection at the junction box. This was probably 10 years ago, but I remember it well because it drove me so crazy trying to figure it out. I never would have guessed it was the wire connection itself!

 

[98TxTJ]

I wish I could answer your question, as I'm not sure what ground it would be. You'd have to likely tear apart the dash and look for the ground, or see if you can find it in the wiring schematics.

Very funny, because almost the exact same thing happened to my old 2000 XJ I used to own. Literally the same exact symptoms. I tried everything you did and eventually broke out the wiring diagrams and multimeter and started tracing power all the way in from the battery, to the control panel itself.

I found that part of the power wire had power coming through the fire wall, up until the junction box under the dash. At the other side of the junction box, there was no power coming out of that wire at all. It ended up being a loose / faulty connection at the junction box. This was probably 10 years ago, but I remember it well because it drove me so crazy trying to figure it out. I never would have guessed it was the wire connection itself!

We could find nothing that looked problematic. I suspect we'd have to take a lot more of the dash apart to investigate further.

But, everything is working great with the hack. Since there wasn't a lot of hue and cry from forum members that we would fall off a cliff and die a fiery death because of how I fixed it, I suppose it's good as-is.

 

[Chris]

We could find nothing that looked problematic. I suspect we'd have to take a lot more of the dash apart to investigate further.

But, everything is working great with the hack. Since there wasn't a lot of hue and cry from forum members that we would fall off a cliff and die a fiery death because of how I fixed it, I suppose it's good as-is.

Thanks for the update! At least it’s working, that’s what matters.

 

[98TxTJ]

Interesting development:

Since it's been colder, the heat is in regular use on the 12 mile commute in the mornings. The other day, I noticed that the highest setting, the one that bypasses the resistor pack, wasn't working. I rarely use the highest setting so it was a pure accident that I discovered this.

It works when everything is cold. After about 15 minutes, when everything is nice and warm, it quits working on the highest setting.

All other fan speed positions work fine; only the high setting stops.

It's the original fan switch and the blower motor that was in the Jeep when I got it.

Ideas?

 

[98TxTJ]

Interesting development:

Since it's been colder, the heat is in regular use on the 12 mile commute in the mornings. The other day, I noticed that the highest setting, the one that bypasses the resistor pack, wasn't working. I rarely use the highest setting so it was a pure accident that I discovered this.

It works when everything is cold. After about 15 minutes, when everything is nice and warm, it quits working on the highest setting.

All other fan speed positions work fine; only the high setting stops.

It's the original fan switch and the blower motor that was in the Jeep when I got it.

Ideas?

I've continued getting intermittent high speed on the fan with all other speeds working.

Today I got into it, and found that when I wriggled the wire bundle near the connections and relay by the fuse box high speed could be made to come on. I couldn't find any loose connections or burned terminals, and flexing the harness did nothing. The fan motor blew on high the whole time I was futzing around after I got it to come on by tugging the bundle.

By chance, I took off the speaker cover and there it was — a loose ground connection. When I jiggled that wire (which I'd had under tension) I could stop the blower. Tightened it up and all seems to be well again.

I hope.

 

[Jackman]

My blower was working intermittently on high.. now I'm only getting it to work on 2nd speed... Pulled the wiring harness and tried from the control knob and tried jumping the hot wire to all the other wires and only working in one speed. Looks like I'll be replacing the resistor soon...