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Heater Control Circuit

I got my Dayton replacement heater blower motor in place and it is working great. I have nominal heat again. I also learned that the PO of my 86 had ripped out the center fan control console and changed my heater levers to all right side levers, EM brake handle on the left. I have since bought a new console and split heater leavers (EM brake in the middle and levers on each side). Plugged it all in but get nothing from my footwell blowers. I pulled both blowers out, cleaned them, tested them... all run okay. So, I pulled the heater control unit from the back and opened it up. Here's what I see on pin #4...



Ideas on what I should do at this point? Thanks.

-Troy
Old 02-25-2007, 08:53 PM
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Is that burned or just flux?

Here is some reading;

Help! Does anyone understand the footwell blower circuit

and

Engine Compartment Heating Relay

The relay has a reed switch in it that wants to see a certain current going to the back blower to verify there is positive pressure in the heat exchanger. The dayton blowers are smaller and don't pull as much current. Everyone just jumpers the reed switch.
Old 02-25-2007, 11:05 PM
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Hey rick... yes, I've read both of those and was preparing to do the reed switch bypass that everyone was successful with... but upon opening my heater control unit... was a little surprised by all this dark stuff. Looked like it may have gotten hot at some point. But, could be flux. I'll have to examine a little further... would it hurt anything to go ahead and do the bypass surgery on it?

-Troy
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Old 02-25-2007, 11:21 PM
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Quote:
Originally posted by TroyGT
would it hurt anything to go ahead and do the bypass surgery on it?

-Troy
It didn't seem to hurt anything on my 88.
Old 02-25-2007, 11:28 PM
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Cool, thanks rick. I'll do the jumper tonight and see how it goes.

-Troy
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Old 02-26-2007, 06:08 AM
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Its hard to tell from the photo if that is flux or a trace acting like a fuse. I would clean it up to be sure there isn't a burn in the trace and that the trace isn't shorting the either of the 3 solder pads that that surround it. I think the small relay is mounted in that area.
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Old 02-26-2007, 06:40 AM
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I agree with Ron, no burning or lifting of the trace, yet. Solder has melted, though, and run away from relay terminal.

Check the condition of small relay contacts. Terminals 3 and 4 [external] are the contacts for the small relay!

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Last edited by Early_S_Man; 02-26-2007 at 08:57 AM..
Old 02-26-2007, 08:48 AM
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How best to clean up around this? I don't want to make things worse in the process.

Thanks.

-Troy
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Old 02-26-2007, 09:02 AM
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Troy,

Use a small, stiff bristle brush and 90% isopropyl alcohol. Sometimes called acid brushes ... you can get them at Home Depot or other hardware store.
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Old 02-26-2007, 09:09 AM
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Will do... thanks.

-Troy
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Old 02-26-2007, 10:39 AM
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After cleaning this up a little... it would appear that this contact is burnt into. Shouldn't these be connected? Here's another picture of it cleaned...

-Troy

Old 02-26-2007, 03:45 PM
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Here is a pic somebody posted. It looks like the 2 solder joints should not make contact with the trace. Ignore the red line, that is the jumper.

Ian
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Old 02-26-2007, 04:29 PM
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You can repair that break by soldering a suitable piece of solid copper wire across the gap, allowing as much overlap on each side as practical.

For a "belts and braces" approach, remove all existing solder from that trace, and wrap and solder the copper wire around each component connected to the trace. From what I can tell from the picture, it looks like a piece of 18 AWG solid copper wire will work.

Either way, be very careful not to short to the other traces. You can use epoxy to hold the new wire in place. I'll defer to Warren should he have any suggestions!
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Old 02-26-2007, 04:47 PM
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Quote:
Originally posted by TroyGT
After cleaning this up a little... it would appear that this contact is burnt into. Shouldn't these be connected? Here's another picture of it cleaned...

-Troy
Troy,

Yes, the long 90-deg solder path appears to be interrupted (open circuit) probably the result of a high amp demand from the component (relay) above
Old 02-26-2007, 04:55 PM
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Troy, looks like that small relay is toast! The contact/terminal that the solder ran away from has now fallen off/through the board! The residue that was a mystery seems to be melted epoxy resin from the underlying glass fabric!

I think I see what you mean about the copper run/trace being burnt away:

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Old 02-26-2007, 04:56 PM
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OUCH! So the question remains why did it do that? Maybe, dying footwell blowers started pulling a lot of current. You should check to see if you have inline fuses on the footwell blowers and that they are sized correctly..10 amps.
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Old 02-26-2007, 06:02 PM
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Okay guys.... I bridged the gap by solding a piece of 'solder remover' copper mesh into that spot. After doing this, I then flipped over and jumpered the reed switch contacts. Slapped it back together and I now have footwell blowers for the first time. All speeds are good and the heat blows great... I was so happy that I got a ticket for 75 in a 60 this morning while passing a cop on the left side. Heater euphoria... could be.

The only small oddity that I noticed is that the footwell blowers seem to stay on all the time... albeit on very low setting. My rear engine compartment blower stills cuts on and off with the levers. The footwell blowers operate independently of the rear blower... meaning I can turn either on without the the other being on first. Is this by design or do I still have a problem here?

Thanks.

-Troy
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Old 02-27-2007, 07:26 AM
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Sounds like fused contacts on the relay that controls the footwell blowers..[I think its the little guy on the board you repaired/modified]. The solenoid for the FW blower relay should only be getting power when the rear fan relay powers the rear heater fan. You need to have another look at that circuit board and test the relay. Also ck that the FW blowers are fused. You aren't out of the woods yet..ticket or no ticket!
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Old 02-27-2007, 07:55 AM
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I'll have to pull it out again tonight then. My footwell blowers are NOT fused... not obviously anyway. They have an injector connector for power, but I saw nothing near that.

I'm assuming that I've fat soldered something maybe. What do I need to do to test/trace this?

Thanks.

-Troy
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Old 02-27-2007, 09:06 AM
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Troy, The factory started using an inline fuse in 1987 according to the PET. I always thought to was to prevent fires from occuring when the the motors began to bind and pull tons of current. It might also be to prevent the engine controller module from melting down like yours did. I know the controllers are expensive. The relay looks to be easily removed and if there are markings you might be able to replace it. I wonder if you could open a round relay and use the guts??
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Last edited by Mysterytrain; 02-27-2007 at 11:41 AM..
Old 02-27-2007, 11:29 AM
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