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Pete, Mercedes Mechanic
Category: Mercedes
Satisfied Customers: 28315
Experience:  Over 15 years experience as a Mercedes dealer technician
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I have a c300.. the heater/ac is blowing air... it seemed to

Customer Question

Customer: ***** *****.. I have a c300.. the heater/ac is blowing air... it seemed to cut in and out yesterday and will not work today... there is power to the red wire to the resistor but not to the red wire on the blower
JA: Thanks. Can you give me any more details about your issue?
Customer: 2010 Mercedes c300..
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Submitted: 1 year ago.
Category: Mercedes
Customer: replied 1 year ago.
I didn't get a response
Expert:  Pete replied 1 year ago.

My name is ***** ***** I am a professional here at Just Answer. I noticed that your question had not received a response and thought I would see if you still need help with this.I apologize for the delay and I hope I can still assist you with this here.

From what you have described here and with the testing that was done and the common fault that causes this,this sounds like the blower resistor itself is at fault needing replaced.In some cases the blower itself can draw to many amps or short out/fail and cause the resistor to fail with both needing replaced.I can walk you through some more testing if you want so we can make sure these or which of these are the cause here just let me know if you would like to further test this.

If more help is needed, use the reply tab to continue our conversation. If no further assistance is needed, kindly rate my service.You can rate at any time and we can continue to work on your question as this will not close out your question.Keep in mind in some cases it can be difficult to fully diagnose or help repair your vehicle without seeing it and I work on delivering the best possible answer from what I see to work with.

Thanks Pete

Customer: replied 1 year ago.
Please post the test steps.
Expert:  Pete replied 1 year ago.

On the brown wire at the blower test this for a ground with your test light or multi meter connected to a battery power source.This wire should have fluctuating ground signal depending on the blower speed.The higher the speed the more ground it will have.If this is o.k. trace the red wire from the blower and see if there is a break in the wire leading to the resistor.If this is all o.k. let me know so we can continue as well as let me know the date of your vehicle looking at the drivers door sticker there should be a manufacture date on it that will help me look into the correct diagrams as theres two different options depending on the year and month this vehicle was built.

Thanks Pete

Customer: replied 1 year ago.
There IS ground on the brown and power to the red at the blower connector.
Expert:  Pete replied 1 year ago.

If you have power on the red wire at the blower and ground to the brown wire at the blower this indicates the blower motor itself is at fault needing replaced.The blower has the proper power and grounds but isnt coming on.In some cases you can confirm this with the heater switched on and engine running tap on the blower with a rubber hammer or similar.If the blower then runs then the blower needs replaced.If this is not where the voltage is and you are missing a power or ground to the blower let me know.

Let me know if you need anything else and feel free to rate my help.

Thanks Pete