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I have a '90 Legacy wagon. The heater fan usually works when the car is cold, but it stops after it is warm, usually about 20 minutes after I start the car. I pulled the harness off the blower, and it does not get power, so I don't think the blower is the problem. I also replaced the relay, so that's not it either. Any other ides? Thanks!

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Thanks! Yes, when it stops it stops completely. None of the speeds work. Is it it correct to assume that if it were the resistor the highest speed would still work?

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Prolly best to replace the blower motor. It is an ez swap out. Get a replacement from a wrecking yard. Be glad to give you detailed info if you desire.

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Thanks! Yes, when it stops it stops completely. None of the speeds work. Is it it correct to assume that if it were the resistor the highest speed would still work?

That's right, in the highest speed position the resistor isn't in the circuit.

 

Since you've already changed the relay, there are a couple of things you can try next time the blower quits. The first is to rap on the dash in the area of the mode control, and see if the blower comes back on. The other is to remove the relay and see if its coil is getting power -- it should be on pins #1 & #3 of the socket shown in the attached diagram. (Since the relay contacts normally are across pins #2 & #4, you'd see battery voltage across them as well.)

 

Let us know what you find.

post-15889-136027645564_thumb.gif

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Okay, the fan is not working and pins 2 and 4 have power across them, but 1 and 3 do not. It's the same whether or not the fan is turned on.

 

Unfortunately I've been rapping on the dash for a good year now, to no avail ;)

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It may be an issue with the actual HVAC control unit. They are known for bad solder joints that crack and cause intermittant problems. On my car, the mode/door selector wouldn't work.

 

I ended up taking apart the HVAC control unit and soldering the cracked solder joints. Here's my post with pictures and information.

 

http://www.bbs.legacycentral.org/viewtopic.php?f=10&t=1142

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Okay, the fan is not working and pins 2 and 4 have power across them, but 1 and 3 do not. It's the same whether or not the fan is turned on.

The last check is to see if there's power at pin #1 with respect to chassis ground. If there is, then...

 

 

Unfortunately I've been rapping on the dash for a good year now, to no avail ;)

...the mode control is likely the culprit, which is where I was going and Josh went into detail about.

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There is power from pin 1 to ground. Darn, I was hoping it would be anything but the control module.

 

Next question (thanks for all your help by the way!): Is there anything wrong with just putting a switch in to turn the fan on and off, bypassing the control module and relay? This car is on its last legs and I'm hesitant to put much money in it, but it's pretty much useless without defrost and heat. Could such a switch tap into the relay connector?

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I may have answered my own question-- connecting pins 1 and 3 turns the fan on, and the speed selector slider still controls the speed. Is there anything wrong with adding a switch between pins 1 and 3 (other than it being a hack job, which I concede that it is)?

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You could put a switch (capable of handling the blower motor current) in place of the relay contacts. Agreed, it's a hack job, but I understand your circumstances.

 

However, you have me puzzled. :-\ The wiring diagram I have (not factory) shows pins #2 & #4 as going to the relay contacts. It indicates #1 & #3 as going to the relay coil -- assuming that's correct, connecting those two pins together should blow the mode control's fuse, if the ground connection through the control was working. Without the ground (which seemed to be the case), the fuse wouldn't blow -- but either way, connecting #1 & #3 should theoretically not cause the blower to come on.

 

Care to pursue this?

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Sorry, I was wrong-- I should have said that connecting pins 1 and 4 cause the fan to come on. I just realized that connecting 2 and 4 also make it come on. I'm assuming this would be a better place to put a switch, since these are the relay contacts, correct?

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Sorry, I was wrong-- I should have said that connecting pins 1 and 4 cause the fan to come on. I just realized that connecting 2 and 4 also make it come on. I'm assuming this would be a better place to put a switch, since these are the relay contacts, correct?

Okay, that makes more sense.

 

Using 1 & 4 passes the motor current through the fuse and wiring for the mode control, which isn't designed to handle the motor load.

 

Definitely use 2 & 4 only (yes, that's where the relay contacts would normally be).

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Well, I realized that the power to pin 2 isn't switched with the ignition, so I guess I'm back to square one. Any idea if there's power under there nearby that I can tap into that's switched?

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If the fuse for the blower has power to it while the trouble is happening and pin 2 doesn't have power on it then check the connection after the fuse to see if there is a problem there. You will most likely see signs of burning wherever the trouble is at.

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Okay, here's what I finally did: I left the relay in place, and put a switch between pin 3 and ground. That way it still uses the relay to turn the fan on and off, and the power for the relay coil still comes from pin 1, which switches off when the ignition is off. It works well enough to eek a few more years out of this car without having to fork over the $$ for a new mode control. Thanks everyone for all your help.

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