March 24

2013 Mercedes Benz C250 – Heater Blower



Mark: Hi, it's Mark from Remarkable Speaking. I'm here with Bernie Pawlik, Pawlik Automotive in Vancouver, BC Canada. Vancouver's best auto service experience, 24 time winners of best auto Repair in Vancouver, as voted by their customers and we're talking cars. How you doing, Bernie? 

Bernie: Doing very well. 

Mark: So today's victim is a 2013 Mercedes-Benz C250 that had a heater problem. What was going on with this vehicle? 

Bernie: Yeah, this car came to our shop cause the heater blower wasn't turning on. The switch seemed to operate the heater blower, but there was no air being blown. So that's important thing to fix, important thing to have in a car.

Mark: Especially here.

Bernie: Especially here, yeah. When it's hot or cold, it's good to have it, at any temperature. It's cold right now in Vancouver. 

Mark: So, what sort of testing and diagnosis did you do? 

Bernie: So first thing we did was hook a scan tool up to the vehicle and just see if there's any relevant stored trouble codes. There was a trouble code in the air conditioning module, but nothing related to the heater controls, for a I think a solar sensor. What that is, is basically there's an air conditioning system, they usually have a sensor that detects how much light is shining in the vehicle. Perhaps temperature as well, but there was a code for that, but I figured that wasn't really relevant to the situation. 

And just knowing the issues with heater blower motors, you know, not operating. Usually it's one of two things. It's either the blower motor or it's the blower controller. Or in an older vehicle we call the heater blower resistor. And usually one of those two components causes the issue. Sometimes a switch. Very rarely though. 

So after that, it was a matter of getting into testing, accessing the blower motor and the blower controller and testing it. I actually worked on the vehicle myself, accessed the wiring to the blower motor and powered it up. And was actually able to turn the blower motor on by wiring it up. So that confirmed that the blower motor was working fine. So then that kind of isolated down to, well, it's probably the blower resistor. And so it's a matter of just testing the circuits to that. 

So I'll just get in some pictures right now. And you can see some of the things that are going on. So there's the car, nice two door coop. 

2013 Mercedes Benz C250 - Heater Blower

This is a view underneath of the actual blower motor. This big round thing on the left here with the fat wires, these things do draw a lot of current, so they have very large wires. You can see there's a red and a brown wire. These are the wires out of the controller. So I've got the arrows pointing at the wiring here on both ends. But the controller, if you can see my mouse pointer moving around, is this sort of black box thing here.

2013 Mercedes Benz C250 - Heater Blower

We'll have a closer look at that in a second. And this is the power going into the controller. So you can see again, there's a brown and a red wire of same gauge, and there's a little tiny skinny wire. And that's basically how it works is that there's power and ground from the vehicle, and then the skinny wire is basically from the air conditioning controlled unit.

Will basically send a signal to the blower module to adjust the speed of the unit. So needed to confirm those powers and grounds to these areas, which I did, and that there was a signal coming from the air conditioning, computer area, wherever that comes from, confirm that was working. So a process of elimination, the blower module's bad. 

There's a look at the unit. Again, two pins, this is going out to the motor. This is the input side, and there's one extra pin there for some reason not used on this vehicle.

2013 Mercedes Benz C250 - Heater Blower

And a backside view. This is the part that faces into the heater box, and a the heater controller, it generates a lot of heat because what it does, there are resistors inside this unit. And what they do is they resist the current flow to the blower motor. And so there's a lot of heat generated in that process.

2013 Mercedes Benz C250 - Heater Blower

So this unit actually needs to be cooled. And so as the fan blows, it actually blows air onto the resistor section and keeps it cold. In older vehicles, you'd find the resistors actually kind of open wire loops and again, they require the same cooling. This works the same way, it's just more sophisticated. 

Mark: It's a toaster with a fan. 

Bernie: It's a toaster with a fan. Exactly. That's right. Yeah. 

Mark: So why would this blower controller fail? 

Bernie: They just do. You know, as I said, there's really two items that tend to fail mostly when a heater blower won't work. One is the motor and one is the resistor. And they just fail. There's nothing that normally causes them to go bad, I guess a bad motor could cause it to fail, but often the component itself just fails. 

Mark: So you mentioned that it could be one of, even though you said two, there was actually three items. The resistor, the controller, and the blower motor. Are the resistor and the controller together in this? 

Bernie: Yeah, they're the same thing. They're all incorporated into that piece. And the other thing, of course, the switch can be bad, but these cars are even more complicated. I'm thinking of like old cars where you had a switch and that had several wires that went to the resistor and then that went to the blower motor.

Now of course in this one there's less wires, but there's a bunch of computers in the way. In the air conditioning control panel, there's computers, that probably sends a signal to the body control module, which sends a signal to the blower resistor. So I'm not sure on this particular car, but a lot of cars are like that.

So you have like one or two computers involved. And actually this blower controller is actually a computer too. Because it's got the one wire that gets a signal that interprets that signal and adjusts the resistors, basically. So many computers. 

Mark: Yeah. How often do you replace this part in general compared to the blower motor or the switch?

Bernie: Probably motors a little more frequently than the controllers. Switches very rare, almost never. 

Mark: And how reliable are Mercedes C250s? This is a fairly rare car isn't it?

Bernie: No, C class is pretty common. The coop is a little rarer than the four door sedan. Yeah, so that would make it a little rarer, but it's a good car. It's actually a four cylinder, turbo engine, so it's pretty efficient and they seem to be pretty good. I think it's a decent car and certainly a lot more economical than previous versions with the V6 motors. So far, so good. 

Mark: If you're having heater blower problems, or you need service for your Mercedes and you wanna try something other than the dealer, come to Pawlik Automotive. Pawlik Automotive in Vancouver. You can book online at, or you can call to book (604) 327-7112. You have to book ahead. They're always busy. Pawlik Automotive in Vancouver. Thanks so much for watching and listening. We appreciate it. Thanks Bernie. 

Bernie: Thank you, Mark, and thanks for watching and listening.

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Bernie Pawlik

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