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Blowing Heater Blower fuses
Posted by: Aaron65 ()
Date: March 14, 2009 09:34PM

I finally got my heat working right, and now I'm blowing fuses when the blower's running...I'm using a fan that's for a '75 Impala from AutoZone, and I took the old one back and put a new one in (warranty), and it's still blowing them. It sometimes blows in 30 seconds, sometimes it takes 30 minutes. Any ideas? It looks like nothing else is on the circuit...kind of a weird problem. Thanks for any help!

1965 Corvair Monza Convertible 95 4-sp.
1965 Buick Skylark
1965 Ford Mustang
1965 Dodge Dart 170 Wagon
1953 Buick Special Riviera

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Re: Blowing Heater Blower fuses
Posted by: Andrew ()
Date: March 14, 2009 09:45PM

Aren't the back up lights on the blower circuit? Maybe there's a short there accounting for the difference in time before it blows.

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Re: Blowing Heater Blower fuses
Posted by: Dan ()
Date: March 14, 2009 09:53PM

Yes, the backup light switch is on the same circuit. Unplug your reverse light switch light from the transmission and see if the problem is solved. If so, you have a short in your reverse light circuit. In my 66 it was the switch itself and the probem was immediately solved by relacing the switch, which is a pricey little sucker. I know a 65 has a different switch, but that's what fixed my blower fuse problem. Good luck,

Dan
Chandler, AZ
1966 Corsa Turbo Convertible
[corvaircenter.com]

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Re: Blowing Heater Blower fuses
Posted by: aircooled6 ()
Date: March 14, 2009 11:21PM

Did this just start when you put that newer motor in? When you said - finally got it working right - Im thinking that the hi-speed motor is just too much for the old wiring. Reach up under the dash and feel the back of the switch when its running, Ill bet its red-hot.

I bypassed the wiring. A relay in the engine room on a separate wire from the battery - fused of course - and a quick splice into the orange wire that goes to the motor. That takes the big load off the old wires to the dash.

I took the easy route - its on or off, no slower speeds. Of course, I cant EVER remember using anything but high, even when I had the choice.

Everett Wilson
North Richland Hills TX
Where I've needed that heat lately!!

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Re: Blowing Heater Blower fuses
Posted by: "UNSAFE" ()
Date: March 14, 2009 11:32PM

It's resistance or possibly an intermittent short.

The fan isn't the problem if you've already tried 2.



The first thing "I" would check is the fuse box itself.

Are the fuse holders rusty or corroded ?

You do know about the fan relay in the front fender ?????


Do what Matt would do --- replace the fuse with a bolt and watch for where it smokes from first !

PS - don't forget that the fan has to be well grounded or it will create resistance.

You might try a redundant ground for the fan motor.

"UNSAFE"
Kevin Willson
65 Monza
Juneau. Alaska



Edited 1 time(s). Last edit at 03/14/2009 11:41PM by "UNSAFE".

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Re: Blowing Heater Blower fuses
Posted by: Aaron65 ()
Date: March 15, 2009 01:34AM

Thanks for all the ideas all. I'll try unhooking the backup light switch (it doesn't work anyway), then check the relay in the fender, then backup ground the fan, then throw the bolt in the fuse box! smiling smiley Oh, I don't drive the car in the really cold weather, so I just figured out that the heater blend door cable was snapped near the control panel, so I crimped and soldered an eye connector to the cable and hooked it up again, so I can open the door for the heat to come in the car...I've had a new fan motor in there for over a year, but the problem just started...then again, I never ran the fan motor much because only cold air would come out!

1965 Corvair Monza Convertible 95 4-sp.
1965 Buick Skylark
1965 Ford Mustang
1965 Dodge Dart 170 Wagon
1953 Buick Special Riviera

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Re: Blowing Heater Blower fuses
Posted by: LeeS ()
Date: March 15, 2009 01:47AM

What is the rating of the fuse and how much current does the motor draw?

Rust or corrosion at connectors will ADD resistance to the circuit, thereby decreasing the voltage available to the load, in this case, the heater motor (engine?). Of course, a corroded connection becomes a little "heating element" and eventually fails resulting in NO current. Unless it shorts to ground and blows fuses; but then your heater blower gets no voltage and doesn't run.

Is it possible that the insulation on the wire to the blower, under the car, is worn from rubbing on something and intermittently shorts against the chassis?

First, what rating fuses are you blowing and what is the rating of the blower?

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Re: Blowing Heater Blower fuses
Posted by: LeeS ()
Date: March 15, 2009 01:59AM

"hooked it up again, so I can open the door for the heat to come in the car."

Could be part of your problem. If the airflow was restricted the motor would overheat and draw excessive current.

Enough heat and the lacquer on the windings can burn causing an internal short in the motor. Of course, you will KNOW if THAT happens by the smoke and smell.

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Re: Blowing Heater Blower fuses
Posted by: Aaron65 ()
Date: March 15, 2009 04:17PM

OK, so it's not the relay (which looks fine), or the backup switch...hmmmmm. No answers yet...maybe the motor draws more than 10A...

1965 Corvair Monza Convertible 95 4-sp.
1965 Buick Skylark
1965 Ford Mustang
1965 Dodge Dart 170 Wagon
1953 Buick Special Riviera

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Re: Blowing Heater Blower fuses
Posted by: LeeS ()
Date: March 15, 2009 04:26PM

Was there a wattage rating on the motor case?

Or, measure the resistance of the blower motor and we can calculate the current draw.

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Re: Blowing Heater Blower fuses
Posted by: Aaron65 ()
Date: March 15, 2009 04:29PM

I have to check the case...I'm not sure how to check resistance on it because it's a one prong plug...

1965 Corvair Monza Convertible 95 4-sp.
1965 Buick Skylark
1965 Ford Mustang
1965 Dodge Dart 170 Wagon
1953 Buick Special Riviera

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Re: Blowing Heater Blower fuses
Posted by: Aaron65 ()
Date: March 15, 2009 06:02PM

No wattage rating at the motor case...it grounds to the frame through the screws...I did the hillbilly thing and popped a 20A fuse in there. I've been reading up on the blower motor I bought at AZ and it is apparently a more powerful motor...maybe it's using 11A or something and blowing the 10A fuse. I ran it for 15-20 minutes on high while driving with the 20A fuse in and it was fine...nothing smoking, no fuses blown. I guess time will tell. I sanded the terminals at the fuse box too...they were a little crusty, but I've seen much worse...

1965 Corvair Monza Convertible 95 4-sp.
1965 Buick Skylark
1965 Ford Mustang
1965 Dodge Dart 170 Wagon
1953 Buick Special Riviera

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Re: Blowing Heater Blower fuses
Posted by: LeeS ()
Date: March 15, 2009 08:20PM

If you have a meter to check the resistance and know how (I say that not to insult you, I simply have no knowledge of your expertise) then what you need to do is to disconnect the plug from the blower, put one lead on the connector on the motor and the other on the chassis. A motor resistance of 1.2 ohms will draw 10 amps when supplied 12 volts. A resistance less than 1.2 ohms will draw more than 10 amps.

Power (wattage) is voltage times current. A more powerful motor will draw more current because the windings have less electrical resistance. More current in the windings produces a stronger magnetic field to turn the rotor.

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Re: Blowing Heater Blower fuses
Posted by: acardon ()
Date: March 15, 2009 10:17PM

My 65 shop manual and 66 supplement says the heater/back-up lights use a 20 amp fuse. ????

The Trunk Belongs in Front, Ask Any Elephant
Caution: Images in This Mirror May be Waterpumpers
Don
NTCA....DFW,TEXAS
66 Monza 1 owner

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Re: Blowing Heater Blower fuses
Posted by: Aaron65 ()
Date: March 15, 2009 11:12PM

Lee...I've hooked up the ohmmeter and got anywhere between a 1.3-1.8...it was hard finding a good ground, so I might replace the screws that hole the fan to the chassis because they're rusty...so it looks like I'm pulling under 10 amps in the motor anyway...*knock on wood* it hasn't blown the 20A fuse yet...but if what Don said is correct it should have 20A anyway! It says 10A on the fuse box, but who knows! Thanks all for the info...

1965 Corvair Monza Convertible 95 4-sp.
1965 Buick Skylark
1965 Ford Mustang
1965 Dodge Dart 170 Wagon
1953 Buick Special Riviera

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Re: Blowing Heater Blower fuses
Posted by: LeeS ()
Date: March 15, 2009 11:38PM

Bear in mind that measuring low resistances, as you are, makes "contact resistance" important to consider. A "good ground" gives you minimal contact resistance. Any readings higher than the lowest resistance you measure are probably due to contact resistance.

Be sure to "zero out" the meter... connect the leads to each other to verify that the meter reads zero.

The ground can be anywhere on the chassis, you just need CLEAN metal.

If you can get a really good reading at the blower motor what I would do next is this:

Re-connect the wire to the blower motor.
Remove the fuse and measure the voltage at each fuse clip, with respect to ground, to determine which is "hot" (12v). The side that ISN'T hot is the one that goes to the blower.
Now, measure the resistance with one test lead on that clip and the other lead on ground (fan switch "on").

This will be the total circuit resistance. Any resistance greater than what you measured directly at the motor will be in the wiring, the switch contacts, and contacts at connectors.

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Re: Blowing Heater Blower fuses
Posted by: CHANCE1 ()
Date: July 28, 2013 05:16AM

if the the fuse block for the fan and back up lights is not usable can u run a wire from the B.U.switch to another hotwire or battery or ??

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Re: Blowing Heater Blower fuses
Posted by: MattNall ()
Date: July 28, 2013 05:27AM

Sure you do lots of different things... but you need to understand basic electrical!







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Edited 2 time(s). Last edit at 07/28/2013 05:37AM by MattNall.

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Re: Blowing Heater Blower fuses
Posted by: CHANCE1 ()
Date: July 28, 2013 06:01AM

THANX this will help a lot .

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Re: Blowing Heater Blower fuses
Posted by: 66vairman ()
Date: July 28, 2013 04:23PM

Aaaron65 ā€“ The heater wire size from the fuse box is 12ga. The current rating maximum is 41Amps if the insulation will tolerate the heat. For minimal loss over longer lengths the maximum current is 9.3 Amps. Iā€™d try a 15 Amp fuse instead of the 20Amp due to connector corrosion, insulation age, etc. Always better to use the minimum fuse value that works even if the wire gauge will tolerate greater amperage.

GM did use a 20 Amp fuse on A/C cars using 12 gauge wire.

BTW ā€“ The primary function of a fuse is to prevent fires.

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