A/C blower motor wiring by-pass. (1 Viewer)

[g-man]

I don't have a blade in position 2 on the plug. No wires to it. Mine is 87 fj60, This is 84 fsm. Can I get some help here? It says "if continuity is not as specified" I know there should be some continuity between the terminals when selecting the corresponding switch position but where is it specified what the ohms is supposed to be?

 

[cps432]

Oh man, you are getting into ohms law... I don't think the manual is asking you to get that specific. If there is electricity flowing through those terminals as described in the diagram the switch should be working.

 

[g-man]

The switch is working but I'm losing EDIT 1 volt from the switch. I put a jumper between the blue/red wire coming from the blower and then to ground. Bypassing the switch. Then tested my voltage at the blower. Now 11.47v So I'm losing 1 volt from switch and 2 from somewhere else.

 

[g-man]

Oh man, you are getting into ohms law... I don't think the manual is asking you to get that specific. If there is electricity flowing through those terminals as described in the diagram the switch should be working.

The manual is asking to resistance test ie ohm test between the terminals. But doesn't specify what the resistance is. Unless it's in a table somewhere else.

 

[cps432]

I see. As electrical components age their original valves wane. You could dig deep into internet files and see if the manufacture of that switch has any archived information on its original specs. That's the only way I could think to get a reference. Or from a new old stock part.

 

[g-man]

@beno is the 60 blower switch NLA? will a 70 series switch fit? Looks like the terminals test out the same but just a different plug.

70 series:

 

[g-man]

Had anyone tried to take the switch apart and clean the contacts?

 

[cps432]

I wonder if there is anything in the last few pages of the manual where all the torque specs are. You could try cleaning the switch with naphtha and some light compressed air.

 

[red66toy]

The grounds for the hvac system are on each of the A-pillars. I cleaned those well and ran an additional ground wire from that point to the battery. The driver's side one is a bit tricky to get to but doable. the passenger side is easy, just pop the glove box out and there it is.

 

[g-man]

Took the switch apart EDIT: (some tarnish of the copper contacts was evident.) and rubbed the contacts with some 600 grit wet/dry sandpaper. Back together and gained a little. Now 11.14v at the blower.

 

[g-man]

The grounds for the hvac system are on each of the A-pillars. I cleaned those well and ran an additional ground wire from that point to the battery. The driver's side one is a bit tricky to get to but doable. the passenger side is easy, just pop the glove box out and there it is.

This is interesting. I may try to do this temporarily and test the voltage again.

 

[Prairie Swamp]

I'm late here - sounds like you're on the right track. The blower recently quit on my '08 FJ Cruiser and the circuit is surprisingly similar. Like I said you're almost there but a few random comments:

- Do you know that the circuit breaker is opening at rated amps meaning 30? Or is it opening at fewer amps being 30 years old.
- There really should be less than a single ohm resistance between switch terminals hence the term continuity.
- 30 amps at 12 volts is 480 watts. That all has to be going to heat somewhere (blower motor, wires, ground connections.) The fact that you are finding warm wires is a good find and also the different voltage drops are good info.
- The comment about the corroded copper is a good one. Verified by the fact you're wires are getting hot. Also back in the day the Japanese in particular skimped on the copper - wire sizes were marginal or undersized now 30 years old.
- I didn't see you mention the rear blower or maybe I missed it. If you have one. Chase that path if you have to. Could be pulling current and not spinning.

My FJ Cruiser turned out to be a weird one. I had voltage to the blower and the blower would run on the bench but would not run in the truck. Turns out the relay was coming in and passing voltage, but the contacts in the relay were burned and would pass voltage but not current. I don't think that's your issues. As I said follow the heat those watts have to be going somewhere.

 

[Prairie Swamp]

Also I scored a clamp on DC ammeter on eBay years ago and it's worth it's weight in gold when you're chasing something like this or parasitic current draw.

 

[g-man]

@Prairie Swamp thanks for your input.

When it tripped the first thing I did was replace the 30A CB with a new one... but it tripped also.

Thanks for clarifiying the term continuity. I was getting it confused with resistance.

I noticed the ground wires to be much cooler when I directly jumped the blower to ground and got 12.5 volts.

I may try to replace some of the ground wires with larger better wires.

The rear heater switch is off but I easy enough to test for any draw.

The heater relay is out of the equation for now because I have bypassed it and the 30 C/B with a direct wire from battery to the blower. When I can get more volts to my blower and get rid of the heat build up in the blower grounds, I will try and plug the blower back into the harness and see if it doesn't trip the CB.

 

[Prairie Swamp]

You've got a good methodology you'll get it. Wires are resistors so the fact they are cooler now means you are pulling fewer amps through them which is your goal.

 

[John Staton]

I am an observer of this thread ,and guessing I am not alone, as I suffer with a thrown CB after having my AC on high for a bit. Once you guys get your final analysis done I am hoping for a straight forward remedy/advice even a non electrical guy like me can do to get back on high. Something like replace this wire with a higher gauge, replace your blower motor, crimp you CB connector, etc.... Thanks again for sharing your findings with us.

 

[morganism]

I would def pull the blower resistor out of the duct work down by the accel pedal, and clean it at least, replace most likely. It pulls amps at all times except when blower is on high. There are several threads on here w replacement part numbers, and plug configs.

 

[cps432]

I would def pull the blower resistor out of the duct work down by the accel pedal, and clean it at least, replace most likely. It pulls amps at all times except when blower is on high. There are several threads on here w replacement part numbers, and plug configs.

That can definitely cause fluctuations in your current. Old capacitors and resistors are notorious for failure and generally need to be replaced every decade or so to keep a system running top notch.

 

[g-man]

I would def pull the blower resistor out of the duct work down by the accel pedal, and clean it at least, replace most likely. It pulls amps at all times except when blower is on high. There are several threads on here w replacement part numbers, and plug configs.

I am planning on doing this.

Found these resistance measurements for the resistor:


Can anyone who has a functioning part check the resistance from each terminal?
H - Eh = .34 Ohms, H -M = .54 Ohms, M - L = 1.05 Ohms. Readings using Fluke 79 on 40 Ohm scale, corrected for lead resistance.

db3, Aug 24, 2016
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#36Like+ QuoteReply

No mention of resistance in the FSM only to check for continuity between 1 and 2, 1 and 3, 1 and 4.

I assume since my voltage went up from 10.73 to 10.84 my loss on high at the resistor is .11 volts

I am surprised no one has mentioned this yet and I am not an electrician but loss of voltage at the blower may or may not equate to overload or gain of amps at the heater C/B. But it does seem like a good way to measure efficiency in the circuit.

I too have a DC clamp on Amp meter goes to 100 amps. But the problem is getting to the hot wires at different places in the circuit. Most are buried in the conduit.

 

[Prairie Swamp]

The way the circuit is made the resistors are in series with the blower. This then is a voltage divider. The resistors "consume" some of the available voltage (13V or whatever) and leave the rest for the blower. The smaller the resistor value the less voltage it will drop. V=(Current^2) X Resistance. So on fan speed one the resistance would be the greatest (1.05 Ohms) leaving the least voltage for the blower. On fan Max position the resistor is out of the circuit all together and the blower see battery voltage minus losses that we don't want that you are tracking down. From this we can conclude that this type of DC motor the speed is proportional to the voltage applied. In other words it is intended to be slowed down by reducing the voltage. So I think this is unlike some types of AC motors where as the voltage drops they pull more current to keep up.

Up in post 22 I think you have a picture of a loop of wire that you should be able to use your clamp on ammeter to measure current. It might be interesting to get a current reading there on Max speed, then measure the voltage at the blower when it's running then you can calculate a resistance equivalent for the blower (R = Voltage/Current). I bet it's close to the middle reading on the resistor (0.5 ohms) which would split the voltage evenly between the resistor and blower. You still have to find your other losses tho (grounds or the wires themselves.)

I have not watched this particular video. Not only is Eric an excellent wrench he is the king of electrical diagnostics. I have learned so much I throw him a couple bucks a month on Patreon.