Hello all, first time Maverick owner and poster. Just got a '74 4-door a few days ago and just about everything on it works great. In fact the only thing that doesn't work on it is the blower motor. I can actually feel heat in the vents and in the heater box so I'm assuming the heater itself works, the motor just doesn't spin up. Here's what I know so far. When I initially inspected the area, I noticed that the black plug with the orange wire going to the blower motor resistor was partially melted. The connector itself still looked good, but the square plastic sheath around it was melted. Checking the fuse box confirmed that the 14A fuse was blown. For the heck of it I put another 14A fuse in there and kept an eye on it while I started the car. As soon as I hit the dash switch there was a brief moment of noise from the fan housing then the fuse flashed into oblivion. So I have a short or a heavy resistance somewhere but as I'm rather new to this vehicle I'm not sure how to test the components involved. I'm assuming that it's either a bad resistor or a bad motor since the switch works. I suppose what I'd like to know is, how do I test for a bad resistor? The motor's easy enough to test. Thanks all! EDIT: Okay, so I did more testing and I think I've come up with the problem and solution. I'll leave this here in case other Googlers like me stumble into a similar problem and want to know what's going on. I tested resistance across each of the three poles of the resistor to the fan plug pole. The readings were 2.5 ohms, 1.5 ohms and 0.5 ohms. Since it's supposed to be low/med/high those values seemed right. I then tested voltage between the fan plug and the dash plug. Each pole/switch position sent 12-14V through without any problems and didn't cause the fuse to blow, but the motor didn't do anything. I decided that the motor was bad and left the resistor as an 'unknown'. Only after going to the local auto parts place and getting a replacement motor did I stop and think that maybe the multimeter I was using was 'stealing' the power when I used it to bridge the connections. I tested that by hooking the new fan up to the dash switch via the multimeter's contacts then grounding it against the chassis. The multimeter read 12-14V and no motor activity. Then I plugged the new motor into the dash switch and grounded it against the chassis. It spun right up and the fuse held. So yeah, my multimeter was causing problems. Since the resistor comes up with proper resistance values I'm going to assume there's nothing wrong with it and that the reason the fuse didn't blow on the multimeter was because the motor wasn't actually drawing power. Now I get to experience the 'fun' of replacing a blower motor on a '74 with no air conditioning. Yay! If anyone has any hints or tips on an 'easy way' to replace the blower motor I'd really appreciate it. It seems I have to let the car cool, pull the heater hoses, remove the whole heater box assembly then replace the motor?
Chances are that your Multimeter was not the problem if you were using it correctly. It sounds like the reason your old fan motor was blowing the fuse was mechanical/electrical. In other words, It sounds like your old fan motor was mechanically binding up, which was causing a high inrush current with a locked up armature not spinning. Most Multimeters have a very high input impedence, when used for measuring voltage, so that they don't load the measured circuit down too much when measuring across a resistance. The exception to this is in the electrical industry, when "Wiggys" are used to measure AC voltage... and they are specifically used for loading down circuits that are being measured for voltage...and are good for ruling out ghost voltages. The best way to replace the blower motor is to remove the whole unit from under the dash. If you do a search...there are several members that have put alot of good info on this proceedure. Good Luck!
Sounds like you got it figured out, but I wanted to clarify something you said. I think you understand it, you just said it wrong. Heavy resistance (or high resistance) does not cause more current to flow, it actually reduces it. This is why poor grounds (high resistance) do not blow fuses. Look at Ohm's law: V=IR. For a fixed V (voltage), as R (resistance) increases, I (current) must decrease for the equality to hold. And the equality must hold, after all it's a law. Good job on the fix!
Ack, how embarrassing. It's rather sad, I can figure things out in my head through experimentation but when it comes to expressing them correctly I tend to make silly mistakes like this. Thanks for the correction! Since the heater works well while driving along I'm putting off fixing the blower for a bit, at least until I can get some time in at my friend's place. I can't do major surgery on the car at my apartment complex so I have to take it somewhere where I can pull the heater hoses without getting yelled at.
you may have something in fan motor impeller, this happens when cars set and little critters get in and build a nest,if you pull the heater out, pull carpet and lay down old towels or something to soak up antifreeze just in case, also while you have it out flush water backwards and forwards several times to flush the heater radiator out while you can.Might save you later on having to repull system
Don't know about the non-AC heater box, but I removed the blower motor from my '72 heater/AC unit without removing the whole unit. Wasn't a bad job. Just had to remove one (?) nut and twist the motor and it came off. Non-AC cars might be different. Mine started making a strange noise which I assumed was the bearing on my new blower motor. More Chinese junk, I thought. Turns out a gas pump receipt had gone down the defroster vent and was hitting the fan. Easy fix for a change.
If I were doing the heater box/blower rebuild, I wud replace the heater core while I had it apart. That will save u the trouble of having to "possibly" do it a second time. The cores are relatively in-expensive, so I think that's the smart way to go...
Had the car at a friend's house and did the replacement a few days ago. There was evidence that someone had been in there before (perhaps to replace a heater core?) and had not disassembled things properly. That's why there was a crack in the lower part of my dash. There were even a few metric (!) bolts here and there in place of SAE. It was a mess. Got it all apart, replaced the blower, put it back together again and only lost the glove box door (my own dumb mistake for not checking whether the ratchet was set to tighten or loosen). Everything works great now! I tell ya it sure is nice having a defroster again!
mine would growl going around corners... come to find out...there was a watch that had fallen down the...defroster vent...
