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Pete
Pete, Automotive Mechanic
Category: Medium and Heavy Trucks
Satisfied Customers: 24658
Experience:  Performed various automotive repairs on several light duty and medium duty vehicles over 15 years of service.
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6NZ in a kenworth, when we turn the heater on defrost the

Customer Question

6NZ in a kenworth, when we turn the heater on defrost the motor overheats and pushes all the coolant out, turn it to floor heat and it stops
Submitted: 1 year ago.
Category: Medium and Heavy Trucks
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.

My info is somewhat limited on your model here but I had seen no one else has responded and would like to see if I can help here.If at any time you feel that I cannot help with this please let me know.

Check and make sure the ac compressor is operating properly and isn't dragging on the engine to much causing this here.In defrost mode the ac compressor engages to dehumidify the air coming out to prevent windshield fog up.If this was already checked and found to be o.k. let me know so we can continue.

If you have an air operated heater control valve if this valve is faulty it can put air into the coolant system and would need replaced.

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.
The ac has been removed and deleted from the ecm, the truck fluctuates as it's about to go and then boom it shoots to 250 degrees but will cool down just as fast? I take it off defrost and it cools down in 2-3 seconds
Expert:  Pete replied 1 year ago.

O.k.,if this model is equipped with an air operated heater control valve this can cause this issue here with it needing replaced.

Thanks Pete