1965 Heater Motor Capacitor

[Joel T.]

Hi Guys;

I've looked at my AIM and my parts catalogs but I can't seem to find a clear picture of the heater blower motor capacitor installation for my 1965. The blower motor was not working (blown fuse). However, upon closer inspection I found the capacitor in series with the hot wire. (i.e. hot lead to capacitor to motor terminal). Unless I'm missing something, this would never work.. Capacitors are AC devices and to not pass DC (at least willingly).

I'll check the cap (it may be fried), but can someone fill me in on the proper installation.

Thanks!!

Joel

[John H.]

Re: 1965 Heater Motor Capacitor

Hi Guys;

I've looked at my AIM and my parts catalogs but I can't seem to find a clear picture of the heater blower motor capacitor installation for my 1965. The blower motor was not working (blown fuse). However, upon closer inspection I found the capacitor in series with the hot wire. (i.e. hot lead to capacitor to motor terminal). Unless I'm missing something, this would never work.. Capacitors are AC devices and to not pass DC (at least willingly).

I'll check the cap (it may be fried), but can someone fill me in on the proper installation.

Thanks!!

Joel

Joel -

It IS a series application at the heater blower - see photo below.

[Wayne M.]

Re: 1965 Heater Motor Capacitor

Hi Guys;

I've looked at my AIM and my parts catalogs but I can't seem to find a clear picture of the heater blower motor capacitor installation for my 1965. The blower motor was not working (blown fuse). However, upon closer inspection I found the capacitor in series with the hot wire. (i.e. hot lead to capacitor to motor terminal). Unless I'm missing something, this would never work.. Capacitors are AC devices and to not pass DC (at least willingly_. Joel

Joel -- I believe the series connection is correct, per '65 AIM U69 sheets; however, Jack Humphrey will probably give us the theoretical explanation (believe he's an electrical engineer). Here's 2 pics of the one I removed from my late 396 --- intentions of cleaning it up, so I connected the orange wire directly to the terminal on the motor.

Curious if your capacitor tab has the same stampings as mine.

[Jack H.]

Re: 1965 Heater Motor Capacitor

Come on guys, it's not rocket science! Look at that capacitor and you'll see it's a THREE port device...

One wire in, one wire out AND a mounting bracket that connects to ground (the blower motor's mounting plate). So, how do you think the capacitor is actually routed?

You're right, it can NOT be installed in series between the two wires. That leaves only one other connection path, eh?

[Joel T.]

Re: 1965 Heater Motor Capacitor

Guys;

I'm attaching a picture of the cap I have... it is obviously a reproduction. I also did a bit of checking with the ohm meter this morning.

Lead to lead is a direct short. which makes sense if this is a series install. Lead to can measures an open which would also make sense if in fact the can is the path to ground for static.... I guess it is the old EE in me (never used however) which led me to the belief that the installation was incorrect.

The heater motor is running fine w/o the cap in series. I also had a blown fuse which might indicate that the lead to can impedance may not hold up under 12V... so we'll try it again later... fuses are cheap enough!

Thanks for all the help!

Joel

PS... Jack, is this correct!?!

[Bill M.]

Re: 1965 Heater Motor Capacitor

Come on guys, it's not rocket science! Look at that capacitor and you'll see it's a THREE port device...

One wire in, one wire out AND a mounting bracket that connects to ground (the blower motor's mounting plate). So, how do you think the capacitor is actually routed?

You're right, it can NOT be installed in series between the two wires. That leaves only one other connection path, eh?

Translation:

The capacitor appears to be in series, and it is mechanically, but can't be electrically: A capacitor is an open-circuit to DC. The capacitor function occurs between the wires and the attachment to the blower motor.

[Jack H.]

Re: 1965 Heater Motor Capacitor

I'm attaching a picture of the cap I have... it is obviously a reproduction. I also did a bit of checking with the ohm meter this morning.

Ohm meter? You're dealing with an energy storage device. It's time to pull out your Digibridge, set it to capacitance mode and measure the storage capacity between either the input or output lead wire and the the bracket/ground. You ought to see something in the 0.2-03 uF range.

Don't have that kind of RLC meter? Then don't be playing with caps and/or inductors trying to assess good/bad health...

Lead to lead is a direct short. which makes sense if this is a series install. Lead to can measures an open which would also make sense if in fact the can is the path to ground for static.... I guess it is the old EE in me (never used however) which led me to the belief that the installation was incorrect.

The heater motor is running fine w/o the cap in series. I also had a blown fuse which might indicate that the lead to can impedance may not hold up under 12V... so we'll try it again later... fuses are cheap enough!

DC motor's create AC 'racket'. The purpose of the cap is to 'hush up' the noise at its source rather than let it travel through the car's electrical system.

Caps block DC and pass AC. The extent to which they pass AC depends on the storage capacity of the cap (that's the 'cutoff' frequency calculation). So, here they've put a 'boat anchor' of a cap (rather large storage capacity) between the motor's B+ supply line and ground.

Unintended AC components generated by the operation of the motor ('noise') have two choices: (1) reflect and ripple along the car's power power line(s) looking for a path to ground, or (2) 'jump' through that nice and conveniently placed capacitor right at the motor's power input and get to ground that way. Nature is 'lazy' and electrons take the easy way out gating to ground through the cap...

The same is true over on the generator (C1 cars) and the voltage regulator. That's why various 'hush up' caps are stategically placed where ever there are noise generating sources.

BTW, anything that switches an appreciable amount of DC power (the voltage regulator, the brake switch, Etc.) IS a noise source since the act of switching is a non-linear function that generates both steady state and transient solutions to an electrical circuit's governing differential equation. It's the transient solution that creates AC components (noise).

On how/why a capacitor across B+ to ground could cause problems, another case of child's play. Caps are to electrical charge what a bucket is to water. Charge in motion (dQ/dt) is the electrical identity for current.

When you measure/confirm the health of a capacitor, you have to take two things into consideration: (1) raw storage (capacity), and (2) dissipation factor (how long/how well does the cap actually hold its charge?).

Suppose I sold you a bucket rated for 2 gallons of storage. But, you're bllind and I 'sharp angled' you. The bucket is indeed a 2 gal pail but it's got a jillion holes in the sides and bottom. Well, I didn't lie, it DOES hold 2 gallons, but not for very long!

The same is true of capacitors. What if the dielectric separating their internal storage plates is aged and riddled with holes? Yep, it's an 0.5 uF part, but it leaks like a sieve!!!

Make the leaks too severe and you start bleeding appreciable DC current through the capacitor. In the case of our heater fan, that would be the equivalent of an unintended DC path to ground in parallel with the motor's power lead!

So, anyone who sells you a used original capacitor has to specify its tested storage capacity (uF) AND report its measured dissipation factor! Dissipation factor ranges from 0 to 1 indicating what percentage of full charge is internally dissipated by the cap in a fixed time interval.

Caps with dissipation factors of 0.01 to 0.10 are reasonably good (they hold/retain 99 to 90% of their charge). Caps with higher dissipation factors are pretty much junk...like that bucket riddled with holes...

[Joel T.]

Re: 1965 Heater Motor Capacitor

I'm attaching a picture of the cap I have... it is obviously a reproduction. I also did a bit of checking with the ohm meter this morning.

Ohm meter? You're dealing with an energy storage device. It's time to pull out your Digibridge, set it to capacitance mode and measure the storage capacity between either the input or output lead wire and the the bracket/ground. You ought to see something in the 0.2-03 uF range.

Don't have that kind of RLC meter? Then don't be playing with caps and/or inductors trying to assess good/bad health...

Lead to lead is a direct short. which makes sense if this is a series install. Lead to can measures an open which would also make sense if in fact the can is the path to ground for static.... I guess it is the old EE in me (never used however) which led me to the belief that the installation was incorrect.

The heater motor is running fine w/o the cap in series. I also had a blown fuse which might indicate that the lead to can impedance may not hold up under 12V... so we'll try it again later... fuses are cheap enough!

DC motor's create AC 'racket'. The purpose of the cap is to 'hush up' the noise at its source rather than let it travel through the car's electrical system.

Caps block DC and pass AC. The extent to which they pass AC depends on the storage capacity of the cap (that's the 'cutoff' frequency calculation). So, here they've put a 'boat anchor' of a cap (rather large storage capacity) between the motor's B+ supply line and ground.

Unintended AC components generated by the operation of the motor ('noise') have two choices: (1) reflect and ripple along the car's power power line(s) looking for a path to ground, or (2) 'jump' through that nice and conveniently placed capacitor right at the motor's power input and get to ground that way. Nature is 'lazy' and electrons take the easy way out gating to ground through the cap...

The same is true over on the generator (C1 cars) and the voltage regulator. That's why various 'hush up' caps are stategically placed where ever there are noise generating sources.

BTW, anything that switches an appreciable amount of DC power (the voltage regulator, the brake switch, Etc.) IS a noise source since the act of switching is a non-linear function that generates both steady state and transient solutions to an electrical circuit's governing differential equation. It's the transient solution that creates AC components (noise).

On how/why a capacitor across B+ to ground could cause problems, another case of child's play. Caps are to electrical charge what a bucket is to water. Charge in motion (dQ/dt) is the electrical identity for current.

When you measure/confirm the health of a capacitor, you have to take two things into consideration: (1) raw storage (capacity), and (2) dissipation factor (how long/how well does the cap actually hold its charge?).

Suppose I sold you a bucket rated for 2 gallons of storage. But, you're bllind and I 'sharp angled' you. The bucket is indeed a 2 gal pail but it's got a jillion holes in the sides and bottom. Well, I didn't lie, it DOES hold 2 gallons, but not for very long!

The same is true of capacitors. What if the dielectric separating their internal storage plates is aged and riddled with holes? Yep, it's an 0.5 uF part, but it leaks like a sieve!!!

Make the leaks too severe and you start bleeding appreciable DC current through the capacitor. In the case of our heater fan, that would be the equivalent of an unintended DC path to ground in parallel with the motor's power lead!

So, anyone who sells you a used original capacitor has to specify its tested storage capacity (uF) AND report its measured dissipation factor! Dissipation factor ranges from 0 to 1 indicating what percentage of full charge is internally dissipated by the cap in a fixed time interval.

Caps with dissipation factors of 0.01 to 0.10 are reasonably good (they hold/retain 99 to 90% of their charge). Caps with higher dissipation factors are pretty much junk...like that bucket riddled with holes...

Jack;

Thanks for all the information... My digibridge went the way of my VTVM and Oscilloscope many moons ago! With my Sears ohm meter I was looking to establish whether the dialectric was broken down or not, at least to the extent one can with a 3V meter.... I agree that beyond this simple test the ohm meter is of no value... The cap is back in the car, and all appears well, but I will keep an eye on it.

Anyway, as some one else said... that while the cap appears to be in series it is actually in parallel.... passing all that nasty noise to ground!

Be well, and thanks again!

Joel