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Pete, Mercedes Mechanic
Category: Mercedes
Satisfied Customers: 27862
Experience:  Over 15 years experience as a Mercedes dealer technician
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1999 clk 430. Heater does not work. code from the a/c heater

Customer Question

1999 clk 430. Heater does not work. code from the a/c heater control is for 123. Evaporative temperature sensor. Could this be casing the unit to not heat.
JA: Have you checked the connectors on the sensor itself? It's important that they not be loose or corroded.
Customer: I will have to find the unit first
JA: Are you fixing your 430 yourself? What have you tried so far?
Customer: I just checked the coolant level, which was the first thing to check. It is full. All the codes in the unit erased. erased
JA: Anything else you want the mechanic to know before I connect you?
Customer: NO
Submitted: 7 months ago.
Category: Mercedes
Expert:  Pete replied 7 months ago.

Hi my name is ***** ***** I will be happy to assist with this today.In some cases I may need more info to assist better.I apologize for any delay.

Do you have air flow from the heater just no heat to it or no air flow at all?

Let me know so we can continue,thanks Pete.

Customer: replied 7 months ago.
Cold air (a/c) flow from all vents. Just cant get warm air, no matter how high you set the temperature ob the unit.
Customer: replied 7 months ago.
Waiting for a response
Expert:  Pete replied 7 months ago.

O.k.,the evap temp sensor code would usually cut off air flow and since you have air flow this isnt causing the issue here with the heater.The biggest issue for no heat is the Duo valve which switches on to allow coolant into the heater core.This is located at the right rear of the engine compartment as shown below.Most likely this valve has failed needing replaced.

The other issue can be the heater core itself being restricted needing replaced or flushed out.If you locate this duo valve you can run the engine to temp and turn on heat and see if the hose on both sides of this valve are hot.If they are then the valve is o.k. Then locate the other hose coming from the heater core that is not connected to this valve and feel it.If it is not as hot as the hose coming from this valve then the heater core is plugged needing flushed or replaced.If one hose is hot at the duo valve and the other is cold or allot cooler then the duo valve needs replaced.

If more help is needed, use the reply tab to continue our conversation. If no further assistance is needed, kindly rate my service,your 5 star rating is appreciated.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