Electrical Load Causing Weak Blower Motor?

[ccitsolutions]

Hello everyone,

I'm new to the forum and hoping to get some advice.

I have a 1985 Chevy C10 square body with an LS swap. Recently, I installed an electronic rearview mirror with an integrated backup camera, along with an amplifier, subwoofer, upgraded speakers, and a few other electrical accessories inside the cab.

Since adding these components, I've noticed that my blower motor doesn't seem to run as fast as it used to. My assumption is that all of the added accessories are drawing enough current that the blower motor isn't getting full voltage anymore. As a result, my A/C airflow has noticeably decreased, which makes it harder to keep the cab cool.

Has anyone experienced something similar? If so, what ended up being the cause?

Would upgrading the alternator, adding a dedicated relay for the blower motor, improving the ground connections, or running a larger power wire help? I'm trying to make sure the blower motor is getting full voltage even with all of the additional electrical accessories installed.

Any advice or suggestions would be greatly appreciated. Thanks in advance!

 

[Ricko1966]

Check voltage at the battery,check voltage at the blower motor. Are they real close. Run a volt drop test. Set your meter in volts mode with the blower on,touch one lead to battery positive other lead to blower motor positive. Do you show more than 1/2volt? Do the same thing negative battery negative post to blower motor ground. Do you show more than .5 voltage on your meter? Those readings explained, if with the blower motor powered on and running, if you read more than .5 volts between the battery + and blower motor + you have a volt drop on the power side. Same thing with neg side, you aren't getting a good ground Example you test positive side and show 3 volts and your battery read 13.5 that would mean your positive lead is only providing 10.5 volts under load you are dropping 3volts on the positive side. Check things first post results and we can trouble shoot from there.

 

[WFO]

Do you have a dedicated heavy gauge wire straight from the battery to your amp?

 

[Sad Sack]

As old as that truck is, I'd throw in a new blower resistor.. super cheap and easy.

 

[Dejure]

If your addtions lowered the power to your blower, it suggests:

(1) Everything is running at the same time;
(2) You're running too much load for the wire size feeding everything; and,
(3) You, likely, are running too big a fuse.

You could do some simple tests:

(1) Run a power line from the battery positive to the resister output wire feeding the blower, which would give it full voltage, which is high speed. If it jumps up, it needs more amperage capacity in the circuit.

Taking after market items off the wire is a better bet than installing a bigger wire.

If the blower goes into high speed mode with a wire straight from the battery, with the other things disconnected, you, probably, and a dirty connection in need of cleaning.

(2) Electrically, temporarily, remove your new adds via fuses or connections and see if you blower comes back up to speed. If it does, you know you are overloading the circuit. And, if you are, the wire should feel hot, suggesting a major future problem, when you least expect and want it.

Hopefully, you have a fair volt-ohmn meter (a MUST for us DIY'rs). Using it, you can put it on volts and see if you get voltage across connections (e.g., probes in wires going into connectors, so you're reading voltage drop across the connectors they go into).

If you get a few volts, then there is a volt drop across the connector. Try cleaning it and test for voltage again.

Re-wire mishaps aside, the heater resistor is an all-or-nothing thing. The power (watts) across the circuit for all three speeds will be the same for each speed. The difference is when lower speeds are connected, some of the power is dropped across the resistor, instead of all dropping across the motor.

I'd give the stereo toys their own circuit.

I'd make sure things were properly fused.

 

[Dejure]

As old as that truck is, I'd throw in a new blower resistor.. super cheap and easy.

That, obviously, won't hurt anything, but blower resistors tend to be all or nothing creatures. That is, they are working or they aren't (they open up). Said another way, resistors don't tend to increase in resistance, instead, they just open [while caps tend to short, then really blow out].

Connections might need cleaning, because they can become additional resistance in the circuit and voltage will drop across that resistance, in addition to the nichcrome resistance wire of the actual resistor.

 

[Ricko1966]

The resistor is out of the picture on high speed. Resistor would only affect lower speeds.My expierience has been a bad resistor you lose a lower speed or speeds entirely.

 

[ccitsolutions]

Thank you all for the suggestions.

 

[Dejure]

The resistor is out of the picture on high speed. Resistor would only affect lower speeds.My expierience has been a bad resistor you lose a lower speed or speeds entirely.

However, qualify that with, one terminal of the resister plug, essentially, acts as a terminal block. The switch high speed feeds into it, and a second wire from the same terminal feeds on to the motor. Thus, as we noted, bypassing the resistor. But it leaves the rare potential for corrosion between the two wires, which would act as a resistance, another voltage drop point.

I've dealt with more than a few wire crimps I had to cut, clean and re-crimped over the years.

In the above case, a voltmeter across the circuit by placing one probe at the blower connector and the other at the switch high speed should give zero volts with 12 volts on the circuit, unless there is a difference in potential on that circuit, such one caused by a corroded connection between the two probes. That could be a couple volts to the full battery voltage, depending on how bad the corrosion was.

 

[Ricko1966]

The high speed is a seperate circuit through a relay. And he'd have found corrosion *anywhere* in the circuit by doing the volt drop test. First thing I'd want to do is verify their is volt drop on either side of the circuit, at tge same time seeing if it us on positive or negative side. No volt drop, no bad connection. Move to a different problem. Such as low system voltage. Which if everything was runningbwhen he checked battery voltage he'd have found at the very 1st. So at that point I'd say it's time for a new motor. Although we could see how many amps the one he has is pulling. That was actually an old trick for finding failing VW fuel pumps replace the fuel pump 16amp fuse with an 8 amp if it pops the fuse the fuel pump was on its way out.

 

[Dejure]

As I pointed out in the past, not always on the relay thing.

Many systems, like mine, do not have and never did have a relay. Schematics and wire diagrams bear this out.

Too, there is the absurdity of putting a relay only on the high speed circuit. At three [or four] speeds should have the exact, same power across the switch the relay is designed to protect.

The difference is, when the blower is on high, all that power is dumped at the motor, while the lower speeds see part of the power dropped across the resistor. The more dropped across the resistor, the less dropped across the blower motor, resulting in a slower speed.

For those unaware, resistors to not block power like a dam holding back water. Rather, they consume power. In a series circuit, like we are talking about here, the total circuit amperage or power/watts would be the sum of the amps or power/watts dropped across the resistor and the motor.

In the course of upgrading my system, I will be installing plug in relays for each of the speeds, since relays are cheap and easy to replace, versus heater-cooling system switches.

Even if one relay quits, as Rick points out, the other speeds will still operate. The only way the blower would stop on all speeds is if there was a problem with the blower of the last leg of the high speed circuit from the resistor output terminal.

The high speed is a seperate circuit through a relay. And he'd have found corrosion *anywhere* in the circuit by doing the volt drop test. First thing I'd want to do is verify their is volt drop on either side of the circuit, at tge same time seeing if it us on positive or negative side. No volt drop, no bad connection. Move to a different problem. Such as low system voltage. Which if everything was runningbwhen he checked battery voltage he'd have found at the very 1st. So at that point I'd say it's time for a new motor. Although we could see how many amps the one he has is pulling. That was actually an old trick for finding failing VW fuel pumps replace the fuel pump 16amp fuse with an 8 amp if it pops the fuse the fuel pump was on its way out.