BLOWER MOTOR AMPERE DRAW

Ross Wooldridge

Old Man with a Hat
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So - further to the saga with my AC vacuum switch and blower motor issues - I bought a cheap ampere gauge to measure the load and startup spike of the blower motor in my 66 T&C, since I was thinking that it was on its way out and drawing too much power, and had subsequently melted/overheated the electrical contacts in the blower motor switch and the vacuum switch.

I can't post a video here without putting it on YouTube first. Going through that rigamarole for a 3 second video is of no interest to me.

Suffice to say that the meter showed an instantaneous spike of nearly 40 amps when starting up, and then almost immediately things settle down to a steady 13 amps running the motor.

Here are two stills from the video:

STARTUP SPIKE 37.5 amps
Frame 1.jpg


RUNNING DRAW 13 amps
Frame 2.jpg


Initially I thought that excessive... even though the blower motor doesn't make any odd sounds, doesn't smell burnt, nothing.

So I tested my spare blower motor on the bench - with EXACTLY the same results.

So, now I think that possibly my first theory is not valid, and that the problem may lie elsewhere.

Thoughts?

FWIW, I have now sourced 3 of the correct AC Vacuum switches, and an additional used blower switch and have an NOS blower switch on the way. Thanks to @Mudeblue, @David Grippin, @Furyman and @Mike66Chryslers for helping me out. So my next steps are to gut the dash and find out where the real problem lies...
 
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So - further to the saga with my AC vacuum switch and blower motor issues - I bought a cheap ampere gauge to measure the load and startup spike of the blower motor in my 66 T&C, since I was thinking that it was on its way out and drawing too much power, and had subsequently melted/overheated the electrical contacts in the blower motor switch and the vacuum switch.

I can't post a video here without putting it on YouTube first. Going through that rigamarole for a 3 second video is of no interest to me.

Suffice to say that the meter showed an instantaneous spike of nearly 40 amps when starting up, and then almost immediately things settle down to a steady 13 amps running the motor.

Here are two stills from the video:

STARTUP SPIKE 37.5 amps
View attachment 616215

RUNNING DRAW 13 amps
View attachment 616216

Initially I thought that excessive... even though the blower motor doesn't make any odd sounds, doesn't smell burnt, nothing.

So I tested my spare blower motor on the bench - with EXACTLY the same results.

So, now I think that possibly my first theory is not valid, and that the problem may lie elsewhere.

Thoughts?

FWIW, I have now sourced 3 of the correct AC Vacuum switches, and an additional used blower switch and have an NOS blower switch on the way. Thanks to @Mudeblue, @David Grippin, @Furyman and @Mike66Chryslers for helping me out. So my next steps are to gut the dash and find out where the real problem lies...

Old Lady Eating Popcorn -2.jpg
 
Just got off the phone with the local grey beard auto electric guy, who confirms the startup and run draw of both my blower motors are ok. He suspects the switches in the dash too.

Sigh - what a pain. Gotta gut the dash.
 
I'm a little surprised at the amount of draw at start-up. The running draw seems about right... and makes a really good argument for doing some sort of relay.
 
Also had my blower motor swith burnt, even though the blower was in perfect condition after being reconditioned. The wiring harness was also tested and checked during the restoration of the car, and was in very good condition.

Best solution as stated above is a relay. Have a new switch, but goes through a relay. I have heard of stories that this often happens. Get a relay, much safer.
 
Just got off the phone with the local grey beard auto electric guy, who confirms the startup and run draw of both my blower motors are ok. He suspects the switches in the dash too.

Sigh - what a pain. Gotta gut the dash.
Hats off to you for exhausting the possibilities to avoid exploding the dash. You’re going to fix it and soon be able to enjoy your dedication.
 
Also had my blower motor swith burnt, even though the blower was in perfect condition after being reconditioned. The wiring harness was also tested and checked during the restoration of the car, and was in very good condition.

Best solution as stated above is a relay. Have a new switch, but goes through a relay. I have heard of stories that this often happens. Get a relay, much safer.

I am a hands on and "follow instructions" kinda guy, using common sense and a measure of common sense.

Can someone provide a clear diagram of how to wire in a relay? What relay to use?

Thanks.
 
Can someone provide a clear diagram of how to wire in a relay? What relay to use?
I've thought about this and it shouldn't be too hard.

My question has always been how to handle the different speeds. The thought has been to avoid voltage drop on high speed and allow the motor to run faster.. But it seems to me that I often run heater fans on lower speeds, so I would want to run that through a relay too. So... Maybe three relays?

Let me think on this...
 
Right - there would have to be multiple relays to allow for the 3 fan speeds (just like there are two relays in the Putco headlight upgrade that @cbarge has had us do - low beam and high beam, and one for fog lamps if equipped).

I too tend to run the blower on high (no resistor in the circuit), but if that's the case, then the setup I have now (direct feed, circuit breaker, heavy duty switch) would suffice, but I do need to have lower fan speeds the odd time.

3 relays - oy... I suppose there'd be room under the hood, but sheesh...

Interested in your thoughts here when you're done.
 
The Putco relays are fairly small... and they'd have to be tied into the circuits before the blower motor resistor, so they'd have to be tucked up under the dash somewhere, and not underhood. It's already packed up there with AC ducts, speakers, radios, glove box, yadda yadda.
 
Smaller relays might be the way to go... There's probably some other solution here, but I'm not seeing it right now.
Could relays be used to supply power to the resistor block? One relay for each speed, and the fan still draws directly from the resistors. Fan switch controls relays only instead of full motor amps.
 
Could relays be used to supply power to the resistor block? One relay for each speed, and the fan still draws directly from the resistors. Fan switch controls relays only instead of full motor amps.
Yes, that is the way to do it.

The resistors drop current so you want them after the relay.. and I think you want to leave them right where they are in the heater box. There's probably some change in resistance with temperature change that is being considered in the design, but it doesn't really matter to us (I think).
 
The Putco relays are fairly small... and they'd have to be tied into the circuits before the blower motor resistor, so they'd have to be tucked up under the dash somewhere, and not underhood. It's already packed up there with AC ducts, speakers, radios, glove box, yadda yadda.
I'm looking at some smaller "micro" relays and when it all adds up, you are gaining an inch in overall width, but height and depth is still the same. Couple that with it's easier to find Tyco relays and associated plugs in the standard size and I think we are better off with them.

I like to use the Tyco relays and while they are a couple bucks more, they are more reliable than some of the others.

Figure the package of relays would be about 3" wide x 1" deep and maybe 2" high (with the plugs). I can gang them together pretty easy too with the plugs that clip together.
 
300% startup draw doesn't sound unreasonable to me.
Yea, I looked it up and 3 to 5 times the running draw is normal, so that factor of 3 is actually pretty good.

The number still just surprised me. Off the cuff, I didn't think it would be quite that high.

Learn something new every day!
 
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