Car fan auxiliary heater

Thread Starter

qwaspen

Joined Dec 1, 2020
14
Hi!
Got a problem with my auxiliary heater.
I connected an auxiliary heater to my car and everything was working great. However, when I added the wiring harness for the car fan, it won’t work. I can only measure 5v at the relay, which is odd since it should be 12v. In addition to this, the car fan stops working entirely when the wiring harness is connected. It’s like the canbus is feeling the extra load and shutting off the fan. Does anybody know how to get around this? Do I need to reprogram the car or can add something to the circuit?
 

Dodgydave

Joined Jun 22, 2012
9,956
Does the Aux heater relay click on when the heater is switched on?

Are you getting 12V at the relay contacts to feed the Aux heater?
 

geekoftheweek

Joined Oct 6, 2013
644
Does the unit actually connect to the vehicle harness at any point? What make model of car and heater? Is the heater switch in the diagram the original factory heater controls, or an add on just for the aux heater?

If you are only getting 5 volts at the relay it could be a bad connection, a fuse that looks good, but isn't (it does happen), or an issue with the harness itself.

As far as the CAN stuff goes as long as you aren't actually connecting to it there shouldn't be a problem. Have you tried with the engine running? It may be possible with the engine off there is some form of low voltage detection turning off non essential loads, but they should come back on as soon as the alternator starts producing power. If you are actually connecting to the CAN then the new heater could cause confusion depending on it's programming and will need someone to adjust settings and such to allow your add on to work.

One other possibility is if you have automatic climate control the aux heater and pump may route too much coolant through it and not allow your normal heater box to warm up enough. Normally there are manual modes which I would assume you would have tried so this point is just something to think about.
 

Thread Starter

qwaspen

Joined Dec 1, 2020
14
Does the Aux heater relay click on when the heater is switched on?

Are you getting 12V at the relay contacts to feed the Aux heater?
Yes the aux heater I also turned on with a 12v relay. I haven’t measured there but I would assume so since it starts.
 

Thread Starter

qwaspen

Joined Dec 1, 2020
14
Does the unit actually connect to the vehicle harness at any point? What make model of car and heater? Is the heater switch in the diagram the original factory heater controls, or an add on just for the aux heater?

If you are only getting 5 volts at the relay it could be a bad connection, a fuse that looks good, but isn't (it does happen), or an issue with the harness itself.

As far as the CAN stuff goes as long as you aren't actually connecting to it there shouldn't be a problem. Have you tried with the engine running? It may be possible with the engine off there is some form of low voltage detection turning off non essential loads, but they should come back on as soon as the alternator starts producing power. If you are actually connecting to the CAN then the new heater could cause confusion depending on it's programming and will need someone to adjust settings and such to allow your add on to work.

One other possibility is if you have automatic climate control the aux heater and pump may route too much coolant through it and not allow your normal heater box to warm up enough. Normally there are manual modes which I would assume you would have tried so this point is just something to think about.
It connects to the blower circuit, in order to start the blower. The car is an Audi A4 Allroad with automatic climate control. Not quite sure about the heater brand. It’s some Chinese stuff.

Okey I will double check the connections.

Yes I have tried with the car running and the fan does not work if the heater harnes is connected to it. It runs for a couple of seconds and then turns off. As soon as I disconnect the heater harness, it works fine.

Yea I have tried manual mode as well.
 

Thread Starter

qwaspen

Joined Dec 1, 2020
14
That looks like the instruction sheet from the heater. Did YOU wire it like they show? The 5V sounds like you pulled it from one of the USB ports in many cars today. What make, model and year car?
Yes it wired like that. It’s connected to the same 12v that starts the heater. The car is Audi A4 Allroad 2014
 

shortbus

Joined Sep 30, 2009
8,594
Yes it wired like that. It’s connected to the same 12v that starts the heater. The car is Audi A4 Allroad 2014
Are you sure the original heater controls use 12V? A lot of stuff in newer cars use the body control module(BCM) to actually control things and the BCM doesn't always use the full 12V of the car.
 

Thread Starter

qwaspen

Joined Dec 1, 2020
14
Are you sure the original heater controls use 12V? A lot of stuff in newer cars use the body control module(BCM) to actually control things and the BCM doesn't always use the full 12V of the car.
I’m referring to the parking heater 12v. The parking heater control unit uses 12v to start the pump and the heater
 
Where does it connect to the blower circuit at? If at the switch shortbus may have the answer.

I also looked up your blower motor for the car and found it looks to be a standard old world two wire motor with a resistor pack. If connected at the blower motor side of things it seems a bit much to say adding a control signal would be enough to trip any current limiter. Something makes me want to say either your harness is shorted or the battery connections are backwards... the only thing missing is the smoke so it's just a guess.
 

Thread Starter

qwaspen

Joined Dec 1, 2020
14
Where does it connect to the blower circuit at? If at the switch shortbus may have the answer.

I also looked up your blower motor for the car and found it looks to be a standard old world two wire motor with a resistor pack. If connected at the blower motor side of things it seems a bit much to say adding a control signal would be enough to trip any current limiter. Something makes me want to say either your harness is shorted or the battery connections are backwards... the only thing missing is the smoke so it's just a guess.
Okey, but how does that explain that the fan isn’t working when the harness is simply attached, and is not receiving current from the heater switch?
 

Thread Starter

qwaspen

Joined Dec 1, 2020
14
Where does it connect to the blower circuit at? If at the switch shortbus may have the answer.

I also looked up your blower motor for the car and found it looks to be a standard old world two wire motor with a resistor pack. If connected at the blower motor side of things it seems a bit much to say adding a control signal would be enough to trip any current limiter. Something makes me want to say either your harness is shorted or the battery connections are backwards... the only thing missing is the smoke so it's just a guess.
It connects to the positive and negative terminal of the blower motor. I will take a picture and show you
 
Have you tried disconnecting all but the connection at the blower motor and trying it? Strip it down to only the harness connection to the blower motor and reconnect things until your fan quits.

Long story short something isn't connected correctly, or the secondary heater is a faulty. Judging from the replacement parts I found for the factory blower I'm confident there is no sort of programming magic that can solve the issue. It's just too old of technology when it comes to the blower motor and how it's powered. The only thing the connection to the blower motor should provide is a signal to tell the heater the fan is on or off. It's possible it may power the relay coil (better schematics would show), but even then it shouldn't knock the fan itself out. All the actual power for the secondary heater should come from the battery connections.
 
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Thread Starter

qwaspen

Joined Dec 1, 2020
14
Have you tried disconnecting all but the connection at the blower motor and trying it? Strip it down to only the harness connection to the blower motor and reconnect things until your fan quits.

Long story short something isn't connected correctly, or the secondary heater is a faulty. Judging from the replacement parts I found for the factory blower I'm confident there is no sort of programming magic that can solve the issue. It's just too old of technology when it comes to the blower motor and how it's powered. The only thing the connection to the blower motor should provide is a signal to tell the heater the fan is on or off. It's possible it may power the relay coil (better schematics would show), but even then it shouldn't knock the fan itself out. All the actual power for the secondary heater should come from the battery connections.
No, haven’t tried that, but that’s a good idea. I’ll try that.

What do you mean with “secondary heater is faulty”? Are you referring to the parking heater? Since it is working fine without the blower I don’t see why it should be faulty.

Am I not right to assume that the relay should be connected to the same signal that powers the parking heater, and then be connected to the blowers positive and negative cable?
 
What do you mean with “secondary heater is faulty”? Are you referring to the parking heater? Since it is working fine without the blower I don’t see why it should be faulty.
I forgot that detail.

Another explanation I didn't consider is instead of the standard resistor pack I originally found it may be some sort of PWM module to regulate fan speed. That may explain why it works for a few seconds then cuts out. Something in the module is getting hot and limiting current. If that is the case it shouldn't take much to find a work around, but still not going to be a programming issue.

Another idea to try is if possible disconnect the blower motor and see if the park heater works with the factory blower disconnected.

A lot of my comments are based on assumptions formed from replacement part listings and scant pieces of schematics I could find online. In the end I hope to have been some help, but if wrong in any way I apologize now. I have no experience with Audi, but more than I care to admit with others.
 

Thread Starter

qwaspen

Joined Dec 1, 2020
14
I forgot that detail.

Another explanation I didn't consider is instead of the standard resistor pack I originally found it may be some sort of PWM module to regulate fan speed. That may explain why it works for a few seconds then cuts out. Something in the module is getting hot and limiting current. If that is the case it shouldn't take much to find a work around, but still not going to be a programming issue.

Another idea to try is if possible disconnect the blower motor and see if the park heater works with the factory blower disconnected.

A lot of my comments are based on assumptions formed from replacement part listings and scant pieces of schematics I could find online. In the end I hope to have been some help, but if wrong in any way I apologize now. I have no experience with Audi, but more than I care to admit with others.
Shouldnt there be 3 cables if it was PWM? How could I work around that?

The park heater work without the blower.

I’ve read on some places that this could be caused by a reverse current and that it can be solved by placing a diode, but I’m not exactly sure where. Should it be placed between the relay positive and the blower motor positive terminal?
 
I was thinking the pwm could be part of the resistor unit I found online. The heat sink on the module started to make me think and i have seen a similar schematic for a different vehicle. Kind of like an in between technologies unit where they didn't fully convert the whole system.

Without actually seeing it i'll just be guessing at anything else... Was hoping for the magical moment where it all clicks and makes sense in my head.
 

Thread Starter

qwaspen

Joined Dec 1, 2020
14
I was thinking the pwm could be part of the resistor unit I found online. The heat sink on the module started to make me think and i have seen a similar schematic for a different vehicle. Kind of like an in between technologies unit where they didn't fully convert the whole system.

Without actually seeing it i'll just be guessing at anything else... Was hoping for the magical moment where it all clicks and makes sense in my head.
The webasto installation manual says that you should connect a cable to pin 3 of the a/c control unit. Is this a canbus signal or can I just attached the positive cable from the relay?
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