Heater switch resistance questions

[72Polara360]

Heater switch for non-AC 1973 Dodge Polara.
Measured resistance at the selector unit's plug where it attaches to the longer harness leading to the resistor.
There are 4 wires, a black (neutral), brown, dark green and light green.

Black multimeter lead went into the black wire socket, and I got the following resistance values in the other sockets.

Off position - all OL
Low position - brown 32ohms, rest OL
Mid position - dark green 1.5ohms, rest OL
High position - light green and dark green both round 1.5ohms, brown OL.

For the electrical Wizards here, would these findings be enough to suspect a pooched blower motor? Or is the switch in your opinion functioning such that it's the reason my fan is not coming on?

My initial reaction is because I don't have an open circuit on all switch positions this switch is not dead and is sending signals to my fan resistor and then to my blower motor when the powers on, so I should be getting some fan action. Resistor looks good by the way.

Thanks for your input

 

[CBODY67]

Usually, the blower motor is the main reason for "no blower motor". As long as the three resistors are still intact, their particular resistance values are not really important. Can you hear the motor physically "thunk" with each speed selection by the switch?

Just some thoughts,
CBODY67

 

[mgm1986]

I am not an expert on these cars like the others here who will certainly be able to help you better with deeper troubleshooting.

Are you able to disconnect the wire to the blower and apply 12v directly to it? This is how I bench tested mine, obviously not as straightforward if you are working under the dash.

 

[3175375]

Did you try to power the blower motor directly as previously suggested?
What happened?

I believe you had posted about this in another thread. No?

 

[72Polara360]

Yes that is my next step, I need to bump test it for sure.
But I'm also worried that my switch might be pooched because in my understanding the resistance numbers should be low all across the board, and when the fan is on high I shouldn't be getting resistance readings on two wires, but this might be my misunderstanding of how the switch works.

 

[3175375]

Yes that is my next step, I need to bump test it for sure.
But I'm also worried that my switch might be pooched because in my understanding the resistance numbers should be low all across the board, and when the fan is on high I shouldn't be getting resistance readings on two wires, but this might be my misunderstanding of how the switch works.

I had issues with the blower operation in both the 69 and the 68. Several poor connections. The blower in the 68 was gummed up but in both cases, poor connections were the largest culprits. I had zero issues with the switches and resistors.

I suggest a slow walk through the entire circuit…

 

[mgm1986]

The "resistors" in my '68 were just springs that, well, created resistance

I don't recall the OHMs but each created more or less resistance that corresponded to the fan speed selector.

Also, I recall having debris in the motor cage that caused some noise. I could see a scenario where something might be lodged in the cage preventing it from spinning.

 

[72Polara360]

I had issues with the blower operation in both the 69 and the 68. Several poor connections. The blower in the 68 was gummed up but in both cases, poor connections were the largest culprits. I had zero issues with the switches and resistors.

I suggest a slow walk through the entire circuit…

I had a look at the harness running further from the plug to the resistor, had the ashtray assembly out and everything, seemed okay. I will try to find some connections at the resistor to check that leg of the circuit tho!

 

[72Polara360]

The "resistors" in my '68 were just springs that, well, created resistance

I don't recall the OHMs but each created more or less resistance that corresponded to the fan speed selector.

Also, I recall having debris in the motor cage that caused some noise. I could see a scenario where something might be lodged in the cage preventing it from spinning.

View attachment 713721

My resistor pictured below looked suspiciously new, I think someone already tried changing it out recently. In my old Thunderbird I had a cooked resistor and I still got full blast fan just no middle speeds, but my Polaras fan doesn't come on at all so I'm thinking at this point it's not the resistor. I wish it had been that easy though it's the most easily accessible part!

 

[3175375]

My resistor pictured below looked suspiciously new, I think someone already tried changing it out recently. In my old Thunderbird I had a cooked resistor and I still got full blast fan just no middle speeds, but my Polaras fan doesn't come on at all so I'm thinking at this point it's not the resistor. I wish it had been that easy though it's the most easily accessible part!

View attachment 713723

The switch is certainly less expensive than a blower motor. Check both the three position switch and the motor.
@Devinism can probably get you a rebuilt one or rebuild yours.

 

[72Polara360]

The switch is certainly less expensive than a blower motor. Check both the three position switch and the motor.
@Devinism can probably get you a rebuilt one or rebuild yours.

That's kind of my issue, i got resistance readings for all speed positions but I'm having trouble interpreting how those readings translate into the health of the switch based on them.

I got healthy looking resistance on green and light green but high resistance on brown (low speed). Still, I feel like this means the switch is not dead (not OL on all speeds).

 

[Big_John]

The one thing I'm not seeing here is a simple check of power from the switch. Checking for resistance is all good, but the simplest test is if there is power to begin with.

You must have a voltmeter if you are testing resistance. A test light would work too. It might possibly have even enough resistance to dim when the switch is moved between positions, where a voltmeter is just going to show 12 volts. Research Ohm's Law to understand that if you need to.

 

[72Polara360]

So this is where my practical and theoretical tend to fall through, I think i get what you're saying, I have a multimeter but I am indeed testing it without power hooked up. You're saying plug everything in and turn the AC power on and maybe go into the back of the plug and see if I have power going through things with the meter on AC? So far yes just been unplugging things and doing resistance.

I know OHMs law V/I/R I just don't have a lot of trouble shooting experience

 

[CBODY67]

Consider "trouble shooting" an "adventure, fact finding, and exploration" operation. To see what is going on or NOT going on. More fun that way.

CBODY67

 

[Big_John]

So this is where my practical and theoretical tend to fall through, I think i get what you're saying, I have a multimeter but I am indeed testing it without power hooked up. You're saying plug everything in and turn the AC power on and maybe go into the back of the plug and see if I have power going through things with the meter on AC? So far yes just been unplugging things and doing resistance.

I know OHMs law V/I/R I just don't have a lot of trouble shooting experience

DC, not AC.

I don't know how much you have unplugged, but yes, plug whatever is disconnected between the switch and the fuse block. You don't need to connect the fan motor.

You can check the wires that plug into the resistor as that's probably the easiest.

And just 'cause.... Did you check the fuse?

 

[72Polara360]

DC, not AC.

I don't know how much you have unplugged, but yes, plug whatever is disconnected between the switch and the fuse block. You don't need to connect the fan motor.

You can check the wires that plug into the resistor as that's probably the easiest.

And just 'cause.... Did you check the fuse?

I will try with power on (yes oops DC it's battery power) and try many more locations!

 

[Devinism]

The very first step would be to see if you actually have power going into the switch on the black wire (key on run or acc)

The resistance between the terminal marked "B" (battery in) and all others should be close to zero when cycling the switch (unplugged).
The high resistance you are seeing on low (32 ohms) should be checked again to verify. Look for scorching on the back of the switch, and possibly a loose "low" terminal.