vnl 730 ac issues, works fine at idle but driving goes hot

It could be the Blend Door Motor or Actuator inside the Dashboard is malfunctioning, giving hot air sometimes instead of cold.

 

Turn the heater hose petcocks off if it goes away you found the problem, if not there is a block in one of your lines or the condenser may be dirty and not allowing enough air to flow. overcharged is another possibility. you have to have a set of gauges and the ability to interpret the findings. That said you can chase your tail trying to find it and spend time and money or you can take it to somebody (like the dealer) that can fix it the first time. Just my 2cents.

 

Tell your shop it is the heater control valve. Common Volvo issue. Kind of PITA to change, small fingers a plus. Good luck.

 

any update? i have the same issue. blows cold when sitting but not when driving. btw where is the location of the heater control valve? is it by the heater core behind the passenger side dash?

 

Yes. near blower motor assembly.

 

good. i was really hoping it was there because i hate it when i have to fix something and its easy and cheap. lol. the ac in this truck has been a pita. so far i have had to replace every line due to corrosion and leaks. only think left is the compressor.

 

If your A/C compressor have some miles i recommand you a simple check : with the engine Off and A/C compressor OFF check with a filler gauge the gap of the A/C compressor clutch, if it's above .031 thousand of inch your problem is possibly come from there. . . . .
When it comes hot under the hood the a/c compressor magnetic clutch resistance increase and the magnetic field decrease if your clutch gap is more than .031(inch) the magnetic field is not strong enough to engage the clutch.
no code are generate in the system.
Let me know. . .
Ben

 

well i do have an update. its not the compressor since all the lines were ice cold so i figured it was the heater control valve. i replaced it which was a huge pain in the ###. checked the ac condenser in the dash and it was ice cold and heater core hot. so i put it all together and it still blew hot air while driving. while sitting in my hot truck with a pack of matches in my hand i remembered that i had blown a hole in one of the metal coolant lines down on my frame that went to the heater core and i had my shop replace them with good heater hose. i had a suspicion and checked them and low and behold the morons had hooked them up backwards. the coolant suppy was hooked to the heater core outlet and vice versa. so when i was idling the hot coolant drained out of the core and ac blew cold but when i starting driving the hot coolant filled up the core and blew hot air. needless to say i had a few "words" with my shop. thanks for all the advice. if the op is reading this, "check the lines" lol