front blower mystery-resistor bypass?

[John Kaufmann]

... Sometime after I tested the 93 blower in the 97 and it blew very weakly on high setting, I had a suspicion that I had not hooked up the connector that goes directly into the blower. I may have only hooked up the 2 connectors that go to the blower subharness. If I'm right, could that be why the high setting only blew very weakly? ...

I wouldn't know. According to the EWD p.144, there are connections from the blower to connector IE2 and from the resistor to IE3. [Connectors IE1 (A/C clutch), IE2 (blower) and IE3 (resistor) are tucked up in the cabin side of the expansion valve. (p.24)] According to p.148, the nominal ohm values for blower series resistance are:

0 (HI), 0.48 (M2), 1.42 (M1), 2.34 (LO).

Of course, that requires both IE2 and IE3 connected; if only IE2, you could still get HI speed, but no lower speeds. If slow on HI setting, that is not a matter of something not connected, but of a high resistance (>2 ohms) in the connected circuit. How you could add a few ohms to that circuit? The blower is possible, of course, as are any connectors, but the most common source of a few ohms would be a scorched switch contact.

[Previologist]

It blew full-on high with the old fan with different brushes though. I guess the mystery will be solved, or become irrelevant, when my new blower arrives. If that one blows soft on high then I'll have to excavate the switch. Here's to hoping that doesn't happen, although its not that hard to get out.

[Previologist]

well the VDO blower was a mistake. The mounting holes are off by a fraction of a mm, I can get them all on but one. Since I'd void the return policy if I enlarged the hole, back it goes for a 4 seasons...

[Previologist]

VDO might have been a blessing in disguise. I was messing around with it and my other 2 when I realized that although the 93 blower mounts and connector are oriented completely different, the 93 does actually fit in the 95 housing. So tomorrow I test it again, making sure to hook up all the wires this time. I may have to lengthen the wires that go directly to the blower because that connector now ends up on the complete opposite side of the housing.

Also I don't know if that little hose that comes out of the motor is an air intake or an exhaust to blow out brush dust, but I had to tape the 93's to the 95's hose so it would reach the fitting. Not sure how important that is, the VDO didn't even have one. Getting the cage off the VDO with scratching it oughta be fun

[John Kaufmann]

... I don't know if that little hose that comes out of the motor is an air intake or an exhaust to blow out brush dust, but I had to tape the 93's to the 95's hose so it would reach the fitting. Not sure how important that is, the VDO didn't even have one. ...

The hose is just for air from a point cooler than the motor itself.

[Previologist]

It should work fine then.

But I'm back to maximum confusion. This 93 blower worked on 3.5 speeds when I plugged it in using it's subharness. But that housing won't work, so when I put it in the 95's housing with the 95's suharness, it only worked on high.

I guess now I need to see if I can switch the subharnesses.

[Previologist]

It should work fine then.

But I'm back to maximum confusion. This 93 blower worked on 3.5 speeds when I plugged it in using it's subharness. But that housing won't work, so when I put it in the 95's housing with the 95's suharness, it only worked on high.

Duhh, that's because the 95's connector to the blower was decapitated (lower picture in post #6) when they ran the wires direct from the front heater relay (upper picture in post #6). So when I use the 95's harness, the resistor is bypassed and I only have high from the direct wire from the relay.

But since high works in that scenario, the reason it only blows slowly on high when using the 93 subharness can't be the switch, if my reasoning is correct. Let me know if anyone disagrees. Because I'm thinking of cutting my losses and wrapping this up, and just settling for 3 speeds. I don't see any reason a new blower would behave differently, so it seems I'm stuck with either high only, or a 3 speed fan with no high. But I save 100 bucks.

I suppose one last thing I could try, and it would be a crapshoot, would be to splice my 93's blower connector into the decapitated wires, and try that. I checked and it does have power.

It would make absolutely no sense if that works, because why would they have cut it off then? But its easy enough to try. Tomorrow. or another day. I'm as sick as anyone of this 2 year old thread but I also don't like being foiled!

[Previologist]

Eff it. I'm going for the switch.

[Previologist]

Things are "heating up"...

IMG_3430.jpg

That right side contact with all the greasey goo on it is the HIGH setting of the switch...so I'll formulate a theory that is probably wrong, but any parts that are right can be credited to John and the others.

Because of the dirty high contact, and additional resistance from other connectors in the OEM wiring harness (at least 8 connection surfaces, 2 per connector), there isn't enough juice to fire the blower at high speed on the high setting. But when using the direct wire from the heater relay, it has less resistance and the blower works on high.

Actually that sounds reasonable. Now to clean this up, add new dielectric grease and put the theory to the test.

[Previologist]

Welp...it seemed like a good theory. But it wasn't. I cleaned up the copper in the switch, di-greased it again and still only low speed on High. I tried the 93 switch too, same.

So in summary:

When I got the 97 van it only blew on high. PO had rigged a wire directly from heater blower relay, bypassing the OEM sub harness and resistor pack

The PO had cut off the harness connector to the blower, in favor of the above direct wire.

When properly wired with the 93's harness the blower only works on 3 speeds. On high it blows similar to low.

The blower worked on high in the 93, and will blow on high if using the direct wire that was rigged by PO from the high blower relay. So it's not a blower problem.

I hear and feel the heater relay clicking when I switch to high. There is a slight delay-if the AC is on the AC light will go off for a second until the relay clicks and delivers power to the blower. That may be normal or irrelevant, I dunno.

I've tried multiple resistors, including brand new and the one that worked fine in the 93.

The switches both check out. The 93 switch worked on all speeds in the 93. Although there were signs of mild overheating in the plastic of both switches, I see no scorching of connectors anywhere, and I cleaned up any minor discoloration bringing shine back to the copper.

The only thing left I can think of is to check all connectors again and then, last gasp, try splicing another blower connector into the 97's harness but I can't imagine that will do anything. And I suppose if I was sure how to go about it, I could check resistance between the blower connector wires and the switch connector. But since they are on opposite sides of the firewall, I think I can forget that. Maybe check the voltage in the decapitated wires on different speed settings?

Just talking to myself to organize my thoughts.


EDIT: So I checked all the connectors (look good) and checked the voltage on the cut connector wires. I wasn't getting consistent readings, but it was under 12 on all 4 settings with engine off, with high only marginally higher than medium, and mid-14's on all settings with engine running. I spliced a connector onto it and lo and behold! No change. Still no high.

So I think one mystery is solved-they wired the blower directly because this problem exists, and like me, couldn't figure out the cause. It must be either in the wiring between switch and blower housing subharness because it was the same with my other blower housing subharness (and which means it will be nearly impossible to access and fix without tearing the entire dash apart), or if the computer is involved maybe its a problem there.

But unless anyone has new ideas, I'm done here. I just have to decide if I want a blower with 3 speeds and no high, or a blower with high only. I think it will be the latter. Many thanks to all who tried to help so far, or if you have any last gasp ideas.

[man_btc]

[edited - screwed up the first time - my apologies]

I agree you probably have a harness problem - your broken connection is probably between:

the switch's "High" contact pin 8 and pin 4 of the "Front Heater (HI) Relay." - so the HI relay coil is never energized (do you hear/feel it click?)
-or-
the motor pin 1 and pin 2 of the HI relay - no path from the motor to ground when that relay is activated. I'd consider this the most likely, since it carries significant current.

(The HI relay's ground (pin 1) and ignition-on 12V (pin3) are from solid bars running underneath the relay socket on the underside of the fuse panel, so there's almost no chance those connections are broken)

As described in the earlier post containing the schematic, the fan switch does two things - once it's no longer in the "off" position, it grounds the coil on the "Front Heater Relay" - so that relay closes and applies voltage to the "+" side of the blower motor. Along with that, the switch also controls the current through the motor by setting the resistance to ground from the "-" side of the blower motor:

- Low speed (shaded bar on the schematic one step to the left, with no connection to the resistor block) = low motor current flows through the entire resistor block to ground (via the "W wire)
- Medium and Medium-High speeds (shaded bar one or two more to the left; switch pins 1 & 2) = sets shorter paths/lower resistance through the resistor block to ground, so more current to the motor
- High speed via a direct motor-to-ground connection through the "Front Heater (HI) Relay" when its coil is grounded/energized by the fan switch in the High position (shaded bar all the way to the left); therefore the highest motor current

If that last connection - the direct path from the motor to ground via the HI relay - is broken, you wind up with the same current path as Low Speed (fan motor pin 1 all the way through the resistor block to ground). That could be because

- the relay itself doesn't work (which you ruled out)
- it isn't activated because there's a break along the path from the switch contact pin 8 to the relay coil pin 4
- the relay closes but the connection to pin2 from the fan motor pin 1 isn't there.

A possible alternative to fixing the harness would be to either

-install a manual switch to bypass the fan switch connection & apply ground to Pin 4 of the HI relay to trigger it
- or -
- placing a manual switch from the fan motor pin 1 (via that blue wire that was added?) to ground. To get High speed, you'd have to turn on the fan speed switch to anything other than Off, then flip your extra switch to bypass the resistor block. In both cases, the original harness would be reinstalled to give you the lower speeds.

[man_btc]

and of course I'm talking going with the original harness to the fan housing

[man_btc]

Maybe this helps?

[Previologist]

Thanks Dan. I'll have to study this a bit. It makes sense but I want it to sink in more.

Perhaps ironically, in a somewhat parallel situation my 97 4runner has a ground issue too but its in the engine running circuit. It has a software ground that apparently went bad, and it would start but would shut off immediately. With help from someone on another forum I rigged a physical switch to ground to bypass the computer ground.