87 B-150 originally AC car.

AC eliminated, but still using original heat box and 'AC' blower, core and control box.

Fan had been blowing weak all fall.

This weekend it stopped altogether.

I checked all fuses (I don't have anything that says which fuse is for what). They are all good (I do have one mystery fuse that does not have power on either end. I had discovered that years ago, so that isn't it.)

I went to check the resistor. There was no power at any terminal of the pigtail.


It was cold and dark. I didn't want to pull the control box, so I just reached.under the dash and made sure the connectors were seated.

I unplugged the fan speed switch pigtail. There was no power to any terminal.

I disconnected the blower hotwire that runs through the firewall and touched it to an upstream side of a fuse. The blower ran, no problem.

Where does it get power from, a fuse, or fusible link?




If i were to bypass the original wiring to get it to work until i have time, daylight and weather to sort it out, what pin do I need to get power to?

Any ideas are greatly appreciated.

The power to the blower switch has to pass through the heater control first. The heater control has electrical contacts (in addition to the vacuum controls for the doors, etc.). These contacts are used to turn off power to the blower when you select OFF.

These contacts get corroded and often melt the plastic around them and get all distorted and lose contact. Take out the heat/cool control and look at these contacts and the 2 wires connecting power through the contacts on the heat control. I reworked mine last summer and it now blows like new.

And yes, there is a blower fuse in the fuse panel. That fuse might be 'blowed' but your low speed all fall is either the heat/cool control switch or downstream at the speed switch and resistors.

I believe Mopar still used a resistor network mounted in the air ducting for speed control. You might want to check that out, too. It's possible you'll have to look under that dash for it, but I'd start out on the passenger's side firewall under the hood first. Look for a small, rectangular phonelic plate mounted to the duct with two screws. It should have a plug attached to it with about 4-5 wires. Remove it from the duct and examine the wire-wound resistor network on the inboard side. Check out the plug and terminals while you're at it.
Went through two resistor networks and the plug in the 12 years I had my '95 Dakota.

Roger

Right. I didn't think of that



They did. It was the second thing I checked:
The blower is grounded directly to the firewall under the hood, so the resistance is to hot, not ground. If there is no power at the resistor, it cannot be the problem.

If the 'off' contacts in the control are upstream of the speed switch, I think that explains all that I have found so far.

I'll see if I can pull the main connector from the controller without removing anything (otherwise it needs to wait until the weekend), and check all the terminals on fat wires for (+) voltage. If it is present I'll pull and clean the control, otherwise I think I have to chase wire from the controller to the bulkhead connector.

Thanks for the replies.

And on the heat/cool control, since you had AC, there are 2 switches; the switch that is 'piggybacked' on the control is for the compressor (as I understand it). The 2 stab-on terminals that are 'more integrated' into the switch body are the blower power control.

This 'sticky' article linked below on the ForABodiesOnly forum has good pix and info on this switch; the control shown in this article does not have the compressor switch so yours will likley look more like the one in the Classic Industries catalog.
http://www.forabodiesonly.com/mopar/sho ... p?t=261388

When I rebuilt mine, I used some sliver loaded dielectric grease to make the contacts more conductive. This can be found on ebay for about $25-30 for a small tube, but can be used in the bulkhead connections and if you have to rework things like the headlight switch.

Thanks.

I don't see me taking terribly heroic measures getting this box to work.

I have been on the hunt for years for a non-ac heat box and control.

Once (and if) I find one, this one is trash.

I may just hack in a toggle switch or something if I discover anything that would not be remedied by a good cleaning.

(I have already replaced way too many parts that are not transferable to the non-AC box. I'm kind of sick at throwing time and money at it, but am not too keen on driving with iced over windshield, or my toes freezing, either.)

Thanks again.