(DIY) AC or Heater Only Blowing on HIGH? Here's a fix

Oh it goes way back and finally in 2011 ToyMoCo released this TSB:
T-SB-0149-11.pdf

You can get the OEM parts or the ACDelco kit which is less expensive but the same parts. FWIW our HVAC system was designed and made by GM. And it was they that came up with the fix because the same problem occurs on the Colorado truck and some others. You occasionally see reference on the GM sites to using the Toyota TSB because they do not know of the ACDelco kit.

 

7 months later, or rather being back in the season of using my heater a lot, and it's acting up again. Wiggled the connector and it started working not just on high, but figured I'd update the thread since it didn't last long.

 

In reviewing this further, in light of my repair being short lived, I'm a little confused as to how this TSB fixes the issue.

The TSB replaces the resistor with an updated version, but uses the same stock wiring as a replacement. So it's saying the overheating of the connector between the wiring pigtail and resistor is caused by a bad resistor design, not underrated wiring, and thus the new resistor paired with fresh (though same) wiring will alleviate the issue? I thought the issue was an underrated wire gauge, which caused overheating issues.

 

Sub'd

 

Check your crimping technique against the info here https://www.tacomaworld.com/threads/diy-build-and-install-a-bussmann-rtmr-fuse-relay-block.399454/

The end most crimps should be on the insulated part of the wire, not the stripped wire itself.

Good stuff nonetheless! Good luck.

 

The issue is not the wire size or the resistor. The problem is a loose fit between the male and female terminals. This loose fit is acting like a heater as all a heater is the presence of resistance in a wire. This in turn causes the terminal to get looser and looser until the fan doesn't run any longer and the connector is fried.

The wire size is fine for the current level. If the wire size was an issue the entire wire would be burned, not just the area next to the terminal.

Replace the connectors Both of them and you should be fine.

Check the plug that goes to the resistor connection and the white plug that goes to the motor? If they have burn marks you need to replace the connector plugs.

Part number

$13 90980-10916 6" 12ga Harness New

90980-10916 Connector

Part Number

$10 82998-12380 90980-10916, 6"es 12 Gauge Wire Harness

82998-12380 Wire and terminal

Not sold as a kit, sold as each. So you will need one of the plugs and two of the terminal and wires.

Connector:





Terminals:



You may also have a burned resistor connector and may need these:

Plug Number:

$31 82141-04M40

82141-04M40

Resistor Number: 87138-04052

 

So why does the TSB only address the resistor? It’s the only updated part, the wiring is just replaced, which wouldn’t address the connector sizing issue.

I’m competent with electrical theory and components, so I understand your explanation, but it doesn’t jive with the TSB or some key elements of the problem.

Also, the wire can be underrated slightly and still have a prominent problem area at the connection. It’s the choke point of high resistance in the circuit and thus the focal point of heat dispersion. Which is why the connection can be burnt and not the entire wire. This is also my reasoning for my initial repair procedure that simply addressed the connection as worn over time. This isn’t a typical low mileage failure, but rather a longer term issue, which speaks to its wear versus horrible design issue. I figured, based on the TSB, there might be more of a primary wear issue with the resistor that lead to eventual connection issue vs it originating at the connector, which is why the resistor was redesigned and the connection was simply replaced with new.

Thoughts?

Jake

 

If the wire was too small for the current drawn then the entire wire would show signs of overheating, not just at the connection terminal. The added resistance at the loose fitting terminal would cause a reduction in current not an increase. The resistance would expend the energy loss as heat concentrated at the point of resistance ( heater ). That is why you would have a burn point localized to the connector. I have taken a soldering iron and applied a tinning coat to the male connectors to alleviate this issue on other components as a short term fix.

As for why Toyota changed the resistor packs is the older ones did have quality control issues and they changed manufacturers. I cannot speak for why they didn't replace the connectors. Ask them.

Those are the facts, take them or leave them. I've been doing automotive electronics for more than 40 years and I currently work for a world wide tier one automotive parts manufacturer as an electronics tech. I'm not trying to bull shit you.

 

You may not be BSing intentionally but your argument is contracting itself, claiming I said things I did not and lacking some critical information. I work as a design engineer, so I'd argue my credentials are equally as valid as yours, sir. My intentions here aren't to have a pissing contest with you though, it's to prove the theory of the real problem and determine a solid fix. If this can remain a discussion, I'm happy to have it.

Originally, my initial fix was based on an improper diagnosis of the problem and I ended up fixing a symptom. I tried replacing the connection thinking it had failed only over time due to constant overheating and eventual wear causing the ultimate failure, which is true in part, but it's not the main issue.

Leaning on the information presented in the TSB Toyota issued, they seem to indicate the issue originates in the blower motor resistor, which I didn't initially take into consideration. If their fix is to replace the resistor with an upgraded design and nothing else, then it's clear where the issue exists.

Understanding their findings, it should be clear that failure is cause by an improperly rated blower motor resistor. Specifically it had too low of resistance and the new updated unit has a higher resistance.

Resistors in series will all pass an equal amount of current. For this discussion, the connector and the blower motor resistor are both viewed as resistors in series. The connection wasn't intentionally designed as one, but it's functioning as one. If the current flowing through the connector is too much, which it is as evident by the burnt connection, then it's due to the fact that the blower motor resistor is allowing too much current flow in the entire circuit. If the new blower motor resistor was built with more internal resistance, it would lower the current passing through the entire circuit....meaning the connector would see less current passage too. This lowered current draw prevents the overtaxing on the connection and prevents it's eventual failure.

So, the correct long term fix is going to be to replace the blower motor resistor with the updated unit and replace the damaged connector. Replacing the connection only is a temporary fix.

If you feel I'm wrong, I'd happily hear your explanation of where you think I went off track.

Jake

 

Can you explain this further? Too much current equals a higher motor input, aka speed? Don't it?

 

I had been experiencing this problem! When I looked at the plug connections I could see the burnt parts showing that there was some shorting going on, So I cleaned the inside with a pin and greased it and made it fit tighter! It worked! I found this thread today! If I have any more problems with it I will know what to do next! Thanks for the post!!!

 

Correct, more current would equal a higher fan speed. A variable fan speed, based on how much current flow there is, is the exact function of the blower motor resistor itself.

With Ohm's Law in mind, the trucks electrical system is providing a constant voltage supply to the blower motor circuit. The blower motor resistor will change the amount of resistance (ohms) added to the circuit which will in turn allow full current passage (high fan setting) or a reduced amount of current (lower fan speeds) to flow to the blower motor.

My thinking is the original blower motor resistor was introducing too little resistance, allowing too much current to flow through the connection, specifically the white wire with blue stripe. Probably only a little too much, based on the fact that the connection can withstand the overload for a long time (mine lasted 8 years).

The updated resistor could have a little more resistance built it in, in an effort to choke down the overall current flowing through the white wire with the blue stripe, again, nothing dramatic that you'd notice in the fan speed, just enough to lower the strain on the wiring/connection.

Jimmy and others can still have a valid point on the connection being too loose, which would cause a potential failure point as heat builds up in that high resistance connection, but it's not the entire problem, IMO. To fix it correctly, I would argue BOTH need to be done; replace the resistor with the updated version and replace the aforementioned connection.

Once the connection has been damaged, replacing just the resistor will leave a failure point at the damaged connection.

Replacing the damaged connection only (or modifying it to be a lower resistance connection) will help, but doesn't ensure a fix. If the connection isn't low enough resistance to handle the slight over current situation, then it'll reoccur. If you can create a connection that's low enough resistance to flow the current without issue, then in theory you could avoid replacing the blower motor resistor, but it'd seem to me, the $30 updated BMR is a cheap enough part to not have to wing it over.

 

NOTE: I bolded my comments to differentiate my comments from yours.

Where did my statement contradict or contract itself?
Where did I claim you said something that you didn’t?
What critical information was lacking?
Design Engineer is so vague.
What type of design engineer? Electronics? Mechanical?
And for how long have you been a design engineer?

I am not trying to nitpick, I only want to know where your qualifications are. As I stated I work with these same automotive connectors every day and have for quite some time. It isn’t like I haven’t seen this issue before in many types of circuits.
I love design engineers, they provide me with job security.

Read the TSB again, The resistor assembly replacement was corrected with the TSB by replacement of the Resistor Assembly and the 4 loose fitting connector terminals. The fuse for that fan and the parallel load ( A/C Amplifier ) is rated at 50 amps so that wire should be at least a ~10 gauge single core which is rated at 52 amps max current. The only way that blower is going to exceed the rated current for that wire is if it locks up or a short circuit to ground. Then the fuse would blow.

Can you document the difference in resistance of the three resistors between the old and new resistor assemblies as you claim they must be different?

Well there are three blower motor resistors in the assembly along with a fusible link.
The resistor Pack controls the current to ground with respect to the speed selected.
The resistor pack is used in series with the Low speed, Medium 1 speed, and Medium 2 speed.
High speed goes directly to ground via the selector switch without using a resistor in series.
All speeds have a parallel resistor in the resistor pack that goes directly to ground.

So no it is not as simple as a series circuit as you state. There are at least 2 parallel loads with the motor on every speed. 1.) The parallel Resistor in the assembly and 2.) The A/C Amplifier which drives the Servo Motors. So the currents in each parallel leg could be and probably are different.

I stand by my statement that if the overall current was too much for the wire the entire wire would be burned and not just localized at the connector. The issue is not an over current problem, but is a resistance problem with the connector terminal acting as a heater. The added resistance of this terminal would in fact drive blower current down.

Anyway, No pissing contest here. You are entitled to your theory's and opinions.

 

First off, thank you for the amazing contribution.

Here's the simplest, easiest, and probably fastest solution at almost the lowest cost:

Skip the trouble shooting of trying to figure out which 1 component to buy and instead go to Autozone and buy the blower and the chip/regulator for $100 combined with a lifetime warranty that stores on their computer with your phone number. You'll probably have to buy the two wires and pigtail connector that plugs to the blower at the dealer/online. Throw away all the old crap and put the new stuff in with less than an hour's work if you're fast (it's a simple job) and never worry about it again.

 

Where did my statement contradict or contract itself?
You keep noting high resistance in the connector and claim it has nothing to do with the current flow. A high resistance connection is only made worse by flowing current through it. So they can be directly related, yet you're shrugging the amperage portion of the problem out of the equation. Add to that, you still don't have a explanation for why 1 connection, out of 4 identical ones, is problematic. If all 4 are identical in size and mechanical fit, why would one reason this one connection fails? I'm only making the claim that it's because the part of the equation that isn't equal among the parts; current load.

Where did I claim you said something that you didn’t?
"The added resistance at the loose fitting terminal would cause a reduction in current not an increase." I took this as a claim that I was arguing there was a current increase. I realize now it may have just been a point, not a claim to what I was saying.

What critical information was lacking?
See response to "Where did my statement contradict itself?"

Design Engineer is so vague.
What type of design engineer? Electronics? Mechanical?
And for how long have you been a design engineer?
I'm a Corrosion Engineer. I design, maintain and troubleshoot corrosion prevention systems for large gas/oil utilities, so I deal with electronics, mechanics, chemistry and much more. I've been working in this field for roughly 14 years. I guess if years of experience is the measuring stick, your opinion outweighs mine.

I am not trying to nitpick, I only want to know where your qualifications are. As I stated I work with these same automotive connectors every day and have for quite some time. It isn’t like I haven’t seen this issue before in many types of circuits.
I love design engineers, they provide me with job security. ]
(this is where the pissing contest seems to exist with you, BTW, these little jabs you insist on) I get what you're saying though. I work in the field and I understand the issues that arise due to engineer designing stuff behind a desk, without a real world understanding of how/what factors apply beyond the ideal world of design software.

Read the TSB again, The resistor assembly replacement was corrected with the TSB by replacement of the Resistor Assembly and the 4 loose fitting connector terminals. The fuse for that fan and the parallel load ( A/C Amplifier ) is rated at 50 amps so that wire should be at least a ~10 gauge single core which is rated at 52 amps max current. The only way that blower is going to exceed the rated current for that wire is if it locks up or a short circuit to ground. Then the fuse would blow.
I went ahead and read the TSB again. You're correct, they did claim to update the design on the connector as well (which I previously claimed as remaining the same, I based this on part numbers, I was wrong). That said, I haven't argued against the connector issues. Though I did question it as the ONLY potential issue, as you're claiming.

Can you document the difference in resistance of the three resistors between the old and new resistor assemblies as you claim they must be different?
I cannot. That lack of information concerning the updated resistor neither helps you or I, though. I still stand by my assumption that since it was noted as an updated part in the TSB concerning the problem, something was changed specifically to address the problem. It makes logical sense that it could've been due to resistance change, leaning on the details of the problem it addresses. Though there's always the possibility it was due to a QC issue (or...both). You've argued it's a QC issue only though, which is an argument with as little proof to back it as my claim is. So it's a mute point unless one of us can bring more info to the table.

Well there are three blower motor resistors in the assembly along with a fusible link.
The resistor Pack controls the current to ground with respect to the speed selected.
The resistor pack is used in series with the Low speed, Medium 1 speed, and Medium 2 speed.
High speed goes directly to ground via the selector switch without using a resistor in series.
All speeds have a parallel resistor in the resistor pack that goes directly to ground.

So no it is not as simple as a series circuit as you state. There are at least 2 parallel loads with the motor on every speed. 1.) The parallel Resistor in the assembly and 2.) The A/C Amplifier which drives the Servo Motors. So the currents in each parallel leg could be and probably are different.
I didn't say the entire circuit was a simple series circuit, I was only referencing these two back to back components. Should the resistance of the blower motor resistor change, it'd change the current flow through the resistor as well, irregardless of the rest of the circuit. The parallel legs have no effect on my breakdown as they don't occur between the two components I'm describing.

I stand by my statement that if the overall current was too much for the wire the entire wire would be burned and not just localized at the connector. The issue is not an over current problem, but is a resistance problem with the connector terminal acting as a heater. The added resistance of this terminal would in fact drive blower current down.
Let's get real specific here, concerning the connector only and nothing else; I'm not saying your stance on the connector being a high resistance connection isn't correct. I'm just trying to point out that "high resistance" is relative. What if we were flowing 1 mA through that connection, would it dissipate that little current in a way that'd lead to a burnt connector? The answer is no. The current dissipated as heat with that low of current flow would be insignificant. As we increase the amount of current flowing through the connection, the current being dissipated as heat increases. So, for the condition of a burnt connection to exist, the following is true: the resistance of the connection was too high FOR the amount of current being passed through it.

On that same front; the amperage flowing along the wiring CAN be too much for the wire without being so much that it burns the wire up. The excess current can effectively been vented off, in the form of heat, without causing actual wire damage. This theory is easily proven by touching the wire under load; is it warm? Yes. Where's this heat coming from? Excessive current load being dissipated. Has the wire burnt up? No. Why? Because the excess is effectively managed by dissipating it as heat.

So why is the connector burnt? It wasn't as effective at dissipating the excessive current load. Why? Because it's resistance is higher than the wires. Does this mean it has too high of a resistance or it's passing too much current? Both, as well as being exaggerated by a potential intermittent contact issue due to incompatible sizing between the terminals.

Anyway, No pissing contest here. You are entitled to your theory's and opinions.

Look, we can continue to discuss this, and if you'd like to I'm good with that sir...tis the point of forums.

My main objection to your stance is you're making the argument for folks to simply replace the connection as it's the only problem area.

I'm merely going on to say I believe replacing the blower motor resistor, as part of the repair, is a critical step to achieve a long term fix. Could be because quality control issues, could be because a change in resistance, could be simply because Toyota says to. Whatever the reason, those folks facing this problem should replace both.

Jake

 

No, I never said it has nothing to do with the current flow. In fact I stated from the start that increased resistance would decrease current flow. Ohms Law.

The White wire with the Lavender Stripe always has current through it, the other three Lavender W/Black Stripe and Green W/Yellow Stripe only have current when that speed is selected M1 and M2. The White W/Black Stripe is a ground.

That would be a perception issue on your end. It was only a point of fact.

I only wanted to know where you were speaking from. And I work with these exact automotive connectors every day.

To be honest it was only one "jab", no plural. Since you work in the field and have to actually put "hands on" the equipment then you know or should know what I mean. Serious. No contest at all, Design engineers ( At least the ones we call desk jockeys ) keep me well paid and employed. Because it worked on paper.

As I stated, that wire should be able to handle 52 amps of current. There is no way that motor is drawing over 50 amps unless it locks up or shorts to ground. Discoloration over time is not an issue, the issue is the severe burning at the terminal.

I am basing my assumption from just the visual of the old and the new resistor packs. Plus the old resistor was made in the Czech Republic the new unit is made in Japan. The visual of each side by side says volumes.

I'll concede the point, I was only explaining the entire circuit for clarity.

Well of course Voltage, Current, and Resistance all have to be considered in any circuit design. I would still say regardless, that the wire is only hot at the resistor connector due to radiated heat from the loose connection at the terminal. That wire is rated for 52 amps full load. I will guarantee you that blower circuit is not drawing 50 amps unless it is locked up or shorted to ground. Either of which would blow the fuse.

I agree with replacing the resistor along with the connector. If you have read many of my post about this issue ( and there have been many ) I have always included the information for part numbers of both connectors and terminals along with the resistor assembly. See my post above # 26 with pictures.

To be perfectly honest about what I think the real cause is. People riding in the passenger seat and their feet pressing on the connector. I very seldom have anyone in my truck ( 7 years old ), but me and I seldom run the blower on high speed ( normally the speed below high ). I inspected my connectors yesterday and it shows no signs of heating or burning at all. The white w/lavender stripe wire is as white as the day it was bought. Now I know that isn't proof of anything, but just my thoughts on it due to the location of the connector.

 

Jimmyh,

Your first comment showed that you hadn't read the thread in detail before posting your "fix". Pretty inconsiderate introduction to the thread that I won't try to prove as I think anyone intellectually honest most likely had a similar reaction to mine when reading your initial comment.

All of your comment's tone comes off a bit "holier than thou". It sounds like you believe your professional credentials give you some sort of gravitas that puts you above reproach. However, it seems clear to me that your motivations are more about being proven right and less about finding an accurate solution to the problem we are all experiencing.

I am new here but find it a very welcoming and positive place to spend my time. I have read all of jmanscotch's posts in this thread, as well as remember seeing his name elsewhere in the forum. Jmanscotch comes off as a super considerate, polite, helpful, and respectful gentleman that is interested in solutions to his issues and the camaraderie associated with like-minded people doing the same. He goes out of his way to make sure he does not offend people and is generally the kind of user a forum or community like this thrives upon and can never have enough of.

When he was challenged by someone with a conflicting perspective he thanked the poster for correcting him as he didn't want to be spreading misinformation. This is the correct attitude to have, IMO, especially in a place such as this used for troubleshooting.

You on the other hand have credentials and a horrible attitude if this thread is any indication of how you deal with people. Your tone and attitude make any solution or information you have to provide very hard to accept.

Just the perspective of a new user coming in here fresh with no biases/prejudice, yet. Maybe you're having a bad day and if so I hope it gets better, but you are picking a fight with the nicest guy in here.

Not trying to be mean to you, just telling you the facts as I see them.

Jmanscotch,

Thanks for being awesome. Keep it up.

Disclaimer; I do not know Jmanscotch, I am not Jmanscotch's alt account, and I am sick of typing Jmanscotch.

 

Well let me say that I apologize and I'm sorry if anyone was offended by the tone of my post.

I was trying to state the opinion of someone with a history of working on these type connectors and the problems they present.

I'll back out of this thread and leave you to your problem solving.

 

I don't see a need for an apology sir, we were merely working out differences of opinion on an issue, all in the name of fixing said issue and finding a reliable fix. I welcome that conversation any day, tis the point in life. Try, learn, accept wisdom from others and repeat.

Since we tend to agree on a fix, the rest is just debating the cause and I'm a curious type fella, which is why I'll dive into those details (I presume much like you). So maybe that's indeed ran its course and we can agree to disagree, since the outcome and fix is unaltered by it anyways.

Cheers

 

Jimmyh I wish I could buy you a beer.

I've been putting off this reply because I didn't feel like "getting in to it" with anyone due to my real life forcing me to "get into it" every day with multiple people it seems.

Just when I think I have people pegged, and I am getting even more cynical, I read something like your reply and it shocks the hell out of me.

I was expecting a point-by-point telling off for sticking my big, uncertified nose into a conversation and Jimmyh decides to be the bigger man and take the high road. I feel like posting this as proof humanity still has a chance.

Jimmyh thanks for renewing my faith in humanity a little bit, you're alright.