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Hot to cold heater

357 Views 15 Replies 2 Participants Last post by  plinker17722
So my 2011 c300 sport started doing this recently and has been totally fine all last year but I warm up the car and heater is hot I drive and it’s hot but if I come to a stop it starts blowing cold and I’ve made sure there is no air in my coolant and radiator system. Belt is new and replaced the idler pulleys and tensioner but nothing else different. What do y’all think.
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1989 W124 260E
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MR ELCO This auxiliary coolant pump needs checking out in yout case .. It helps to circulate coolant to heater. so if it stops working hot coolant wont reach the heater system
Font Camera accessory Cylinder Gas Auto part
system .
 

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1989 W124 260E
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MR.ELCO Did say in my post no2 first check the old one ? Auxiliary pump might be just one reason why you have no heat .I would have checked to see if there was 12 volts power to it first ,,,then, once i had found out it was toast then go ahead and replace it .
 

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2011 Mercedes Benz C300 sport
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28 Posts
Discussion Starter · #9 ·
So just to double chk myself because I’m second guessing now. Do you know where I can find the actual relay that runs the aux pump. I checked it again today running full heater power blowing and there was no power to the pump at all. I’m just so frustrated and confused so I took a step back to reevaluate all tomorrow morning. Im off so I can focus and start fresh. Also thanks for the help and info you have provided
 

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MR.ELCO To find your part and be 100% sure of it being the right one.. would be to use yiour vin number
So can you post the vin number But if you dont like plosting it up on here you can send it to me in a private message so i can check the relay part number for you ? ..
 

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2011 Mercedes Benz C300 sport
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Discussion Starter · #11 ·
I appreciate that but I have the correct part but I want to make sure I’m trying to double chk the relay and or fuse to the actual pump. I just checked it again and I have no power to the six pump.
 

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1989 W124 260E
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2011 Mercedes Benz C300 sport
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28 Posts
Discussion Starter · #15 ·
Correct no power at all but the couple days befor it had power but I’ll look at the diagram you sent and keep you posted. Thank you again you have been a big help
 
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