VNL 780 - D16 bunk a/c blowing cold while front is blowing warm air?

I second the blend door motor having the same problem in my pickup right now . Drives did always blow cold passenger side works for hot and Cold. #### dual climate zones.

 

I doubt very seriously the blend door or stepper motor is it. Most likely it is the hot water shut off control valvle in the HVAC unit. It is located right next to the htr core and ac evaporator. Best way to check it is remove top part of dash. Remove front cover off HVAC unit follow htr lines into valve. With heat on temperature should be about the same both sides of the valve. Turn to cold should notice a difference in temp. Does not stop the water 100% but definitely slows it down. If the valve has failed. Replacing it will male you cuss your mother. But if you need to let me know and I will post directions with out ripping the HVAC unit completely out. The most likely cause of you blowing hot out the front and cold in the bunk is either due to the hot water shutoff valve or a plugged ac evaporator core. Feel the evap when you open it up make sure it up s cold. There are voltage checks you can do on the module the valve etc etc. But more than likely it is one of the 2 I listed above.

 

He's trying to get cold air from both not hot air. Don't see how the water shutoff valve has anything to do with that.

 

Let me explain a how a Volvo VNL HVAC system operates. The blower motor is located in the unit closet to the passenger seat. Mounted directly next to the blower is the ac evaporator which magically turns hot air to cold. Above that lying horizontal is the heater core. There is no blend door or block off or any other device that diverts air away or to the htr core or evaporator. The hot water shutoff valve seems the flow of hot water thru the heater core thus allowing the ac system to function and bring us the cold air we all love so much. If the heat position is selected on the control the ac clutch is not engaged therefore not pumping freon (that magical gas that makes hot air cold) thru the ac lines therefore not interfering with the operation of the heating. Not trying to be an ###. I gave been dealing with Volvo HVAC systems in extremely hot, in extremely cold and quite humid climates. What I played out is the most common failures with the symptoms he gave. Not trying to be an ### in my description but if you are unfamiliar with the Volvo ac system you coulc have this guy looking all over and not finding the root cause. I see these 2 problems in probably 90-95% of the trucks displaying said symptoms.

 

Well if you read the post it was his BUNK heater. The BUNK heater has a blend door to control temperature but I agree you know everything. But you should look at the BUNK heater and find out what controls temp and inform me. Have owned volvo trucks for years they all have blend door in the BUNK heater.

 

If you read the very first post he states that he has cold air blowing in the bink and warm air blowing in front with the temp set to cold. That would put the problem in the front hvac unit. Which does not have any diverter between the htr core or the evaporator. Without having the truck to check voltage at the dash mounted control I replied with the most common failures that I see in my shop, and yes I work at a Volvo dealer. That being said, I see a lot of air conditioning issues in my shop. The ac control module is in the dash panel that has the switches. Unless he has the APADS unit then it is a different animal. But the function is the same. If the hot water shutoff valve fails it will allow coolant thru the htr core while the ac is on. If there is no voltage or there is a short it will open the valve. I would be interested in knowing what the code was also. I just listed the typical failures. It is in no way a complete list of all components that could fail.

 

On my 04 sleeper ac wont work if i shut of cab ac.
You may have bad heater shut off valve or whatever is called. Its located in cab hvac. Its leaking coolant when you turn ac on. You can replace it or you can also install shut of valves on the firewall and that way no coolant will ener cab/sleeper. I use that on the summer. Now every time i start truck, in seconds i get cold air. Before when you #### of truck hvac valve opens and let coolant go in heater core

 

I have now ran into this exact problem with my 2007 Volvo VNL 780. It blows cold air in the sleeper and warm air in the cab. I recently had to replace the blower motor and then it all began. Before replacing the blower motor I had ice cold air in the cab. The motor went out and I replaced it then it started blowing hot air ever since. I believe it is the hot water shutoff valve. Could you give me some help on how to change the hot water shutoff valve and where to buy a new one? Or is there anything I can do manually, like manually cut the shutoff valve off where only the ac will work in the cab and not the heat? Then in the winter swap it back to where only hot air will blow??