A/C blower motor hop-up? - Chevelle Tech
Electrical & Wiring Troubleshooting electrical problems.

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post #1 of 14 (permalink) Old Feb 3rd, 19, 9:31 AM Thread Starter
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A/C blower motor hop-up?

I read an old post about some upgrades that a former member did to his A/C blower motor. Unfortunately he has not been posting in approximately 4 years.

The lines that caught my attention were: "I also spent some time to install a Delco made in Canada A/C blower motor and used sticky non-hardening sealant to seal the blower box... the final touch was to replace the hot wire for "hi" blower going to the relay near the vacuum can with a 10 gauge power wire directly from the battery... This helped make the blower absolutely hum on high"

Anyone have any thoughts about the quote above particularly the part about the #10 black wire? It seems to imply that the #10 wire connected directly to the relay from the battery supplies more power to the blower motor than would be supplied with the stock under dash A/C harness. Also wondering about new blower motors versus. The motor on my A/C is as old as dirt and I am thinking that a refresh involving a new motor might be in order. Anyone have experience swapping out an old (maybe original?) A/C blower motor for a new quality brand motor.

Thx Oman
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post #2 of 14 (permalink) Old Feb 3rd, 19, 11:55 AM
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Re: A/C blower motor hop-up?

What year? I always like to check the diagrams before I stick my foot in my mouth.

I can actually see the larger wire supplying better voltage without a voltage drop. Just like the headlight relay upgrade we do to get brighter headlights. A simple test to see if this will get you more flow is to run a jumper cable to the battery + and connect to the lead of the motor. A good ground lead to your motor may also help get better voltage/current to your blower motor.

Sometimes when you have poor flow it's due to blockages in the a/c heater box....like leaves or mouse condominium.

Blower motors do wear out as they age. Simply replacing the motor could get you better flow. I think there is a way to check by checking the resistance in the motor winding. But without having a few motors lying around, I can't tell you what the resistance should be. As the motors age, they build resistance in the winding causing them to slow over time.
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post #3 of 14 (permalink) Old Feb 3rd, 19, 1:25 PM Thread Starter
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Red face Re: A/C blower motor hop-up?

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Originally Posted by DUTCH MAX HEADWORK View Post
What year? I always like to check the diagrams before I stick my foot in my mouth.

I can actually see the larger wire supplying better voltage without a voltage drop. Just like the headlight relay upgrade we do to get brighter headlights. A simple test to see if this will get you more flow is to run a jumper cable to the battery + and connect to the lead of the motor. A good ground lead to your motor may also help get better voltage/current to your blower motor.

Sometimes when you have poor flow it's due to blockages in the a/c heater box....like leaves or mouse condominium.

Blower motors do wear out as they age. Simply replacing the motor could get you better flow. I think there is a way to check by checking the resistance in the motor winding. But without having a few motors lying around, I can't tell you what the resistance should be. As the motors age, they build resistance in the winding causing them to slow over time.
It is a 1972...cannot recall what year the OP's car was. 70 / 71 /72? To my knowledge the three years are all the same electrically the only difference being an extra vac line for the inline heater shutoff valve.

I would really like to find a better squirrel cage for the blower motor, the motors are easy to find new. I have read that the A/C squirrel cage was designed to move a bit more air than the stock (heater only) cage but I can't prove it. Trouble is it appears that no one manufactures the A/C cage any more. At least that seems to be the "word on the street". A big part of the "effectiveness" of the A/C system (perception of effectiveness?) is the amount of air flow we have in the car in question. Witness the speed of the blowers in new cars when they are on MAX...it is like a low grade hurricane!

BTW you helped me dig out info on that Richmond 3.04 1st gear set. Perseverance pays off...I have the gears sitting on my workbench as I type this !!!!!
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post #4 of 14 (permalink) Old Feb 3rd, 19, 2:54 PM
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Re: A/C blower motor hop-up?

Since most of these era vehicles used a 12 gauge wire to run the blower motor on high through a relay, I don't think running a heavier relay feed will help you much.The key to any electrical system is to eliminate the voltage drop by having good wiring and connections throughout. Length of wire does have an effect on voltage drop,especially if it involves numerous spices and or junctions.Rerouting the wire to make the journey from the battery to the blower relay will help some, but if doing a correct restoration is important, this is not doable. A good blower motor should only require 15- 20 amps maximum draw, in which case the factory wiring was more than sufficient when new. A voltage drop test will inform you of any weaknesses in the system, and you may be surprised at how many drops you may find, especially in a 50 year old wiring harness
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post #5 of 14 (permalink) Old Feb 3rd, 19, 3:42 PM Thread Starter
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Re: A/C blower motor hop-up?

Quote:
Originally Posted by modern malibu View Post
Since most of these era vehicles used a 12 gauge wire to run the blower motor on high through a relay, I don't think running a heavier relay feed will help you much.The key to any electrical system is to eliminate the voltage drop by having good wiring and connections throughout. Length of wire does have an effect on voltage drop,especially if it involves numerous spices and or junctions.Rerouting the wire to make the journey from the battery to the blower relay will help some, but if doing a correct restoration is important, this is not doable. A good blower motor should only require 15- 20 amps maximum draw, in which case the factory wiring was more than sufficient when new. A voltage drop test will inform you of any weaknesses in the system, and you may be surprised at how many drops you may find, especially in a 50 year old wiring harness
Agreed on the 50 Y/O wiring harness but the one in question is new from the control panel out to the relays / blower motor. I am 100% sure the motor is 50 years old so perhaps that is my first "target of Opportunity". It is not that it doesn't work....it is more a matter of looking to be able move as much air as the system can.
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post #6 of 14 (permalink) Old Feb 3rd, 19, 4:09 PM
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Re: A/C blower motor hop-up?

The wiring in question is the two heavy wires on the relay and their sources. The relay is fed battery+ voltage. The second heavy wire runs to the blower motor. The switch wiring only sends a message to the relay to close the contacts in the relay to provide direct battery voltage to the motor on high only. All other speeds are controlled by the switch selection through a series of resistors. I don't have a factory wiring diagram for this car, but most were wired this way .Bad contacts in the relay could also cause a drop in voltage. If it were mine, I would activate the high speed and check the voltage on the feed wire from the battery to the relay first and then check the other heavy wire from the relay to the blower motor and compare. All voltages should be within .5 volts of charging system specs,{roughly 13.9-14.5} with the vehicle running.If everythnig checks out good, confirm the ground on the motor. If good, replace the motor
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post #7 of 14 (permalink) Old Feb 3rd, 19, 4:15 PM
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Re: A/C blower motor hop-up?

Talking about high speed, the feed wire is fused from the horn relay, it does not come from inside the cabin.
I personally do not believe that you would see any improvement in blower operation by replacing that wire.

Was it a factory air car?

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post #8 of 14 (permalink) Old Feb 3rd, 19, 4:59 PM
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Re: A/C blower motor hop-up?

Here is my blower hop up, I did this to my 72 Chevy pickup. I think it would be the same on the Chevelle. Here is the thread I made on the truck forum. This thing blows hard AC blower motor wheel project - The 1947 - Present Chevrolet & GMC Truck Message Board Network
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post #9 of 14 (permalink) Old Feb 3rd, 19, 7:03 PM
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Re: A/C blower motor hop-up?

Here is an 87 Monte Carlo
https://www.rockauto.com/en/moreinfo...056372&jsn=471

Looks like it's similar to a 72 blower cage

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post #10 of 14 (permalink) Old Feb 3rd, 19, 11:47 PM
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Re: A/C blower motor hop-up?

Speaking of blower motors and 4th gen Monte Carlo's, when I replaced the heater core in my 86 Monte Carlo, I also replaced the blower motor and the blower speed was much better, I could have dried my hair, the air came out so much more than the old motor! good luck with your car!!

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post #11 of 14 (permalink) Old Feb 4th, 19, 3:21 PM
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Re: A/C blower motor hop-up?

Grounds are EVERY BIT AS IMPORTANT as hot wires. The SAME CURRENT flows through both.

'71 chevelle, 468, TH400, 12 bolt posi w/3.08's, drinks a lot of 87 octane.
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post #12 of 14 (permalink) Old Feb 4th, 19, 3:43 PM
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Re: A/C blower motor hop-up?

The stock system gets it's power through an inline fuse next to the relay on the fire wall which is fed by a 10 gauge wire run over the left fender skirt to the horn relay.

The horn relay also has a 10 gauge wire feeding it from the battery. This 10 gauge wire literally feeds the entire car. With headlights, wipers and A/C on high, it's actually overloaded-moreso at low engine RPM when the alternator has little output.

It would be helpful to re-route the 10 gauge feeding the blower motor's inline fuse directly from the battery, over the right fender skirt. A 10 gauge negative from the battery to the blower mount flange would also help. Move the fuse from the firewall to the new connection at the battery to protect the run.

This will shorten the run by about half, improve the return path (the negative/ground) and lessen the load at the horn relay.

It won't be a day and night difference but the fan will run a bit better. And your lights won't drop as much when the A/C is on.

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post #13 of 14 (permalink) Old Feb 4th, 19, 4:00 PM
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Re: A/C blower motor hop-up?

You could first check the voltage under load at the blower motor to see if there is enough voltage drop to make it worthwhile to run a new power wire.

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post #14 of 14 (permalink) Old Feb 4th, 19, 6:31 PM
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Re: A/C blower motor hop-up?

This is another example of ďa solution in search of a problemĒ.

Replace the worn out old blower motor, clean your connection (power and ground). Replace the in-line 30 amp fuse if the end barrels are oxidized, clean the fuse holder contacts and check your voltage at the blower on high vs. what the system voltage is when the engine is running.

Donít move the power feed. In the factory configuration, the horn relay buss bar is your main power distribution point and has the higher system voltage when things are operating normally. Moving the power feed to the battery (+) will only add a non-designed burden on the charging line circuit.

People need to realize these systems were designed specifically with options and charging requirements in mind.

Changing the motor to something else entirely means you need to calculate the current demands because the motor speed control resistors are designed for a specific load in mind, deviation will affect the voltage drop across them and could adversely affect the wiring if not planned out.

What people donít think about is the fact the squirrel cage may be filthy, blower motor is kapoot, corroded connections and ducts that leak worse then the Titanic due to the old polyester foam seals deteriorated into dust.

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