A/c question...

The valves are located behind the engine, under the transmission, around the flux capacitor, and through the thermocouple.

Simple, really.

 

prob a detroit so the valves,plural,will most likely be on the right(passenger) side and most likely will be the valves that look like an outdoor house faucet.you could have lever type valves but i doubt it.they control the coolant flow basically.experiment with turning them on/off and regulating the heat or lack thereof. I never really open mine completely up,i do as i type this now but what a freak winter,simply because it gets too hot for me in the truck.

you'll get several interpretations i am sure.i was attempting to keep it simple.look under/over/beside everything along the side of the engine as some of the valves are difficult to actually spot and then get to.

 

I'll be honest in saying I'm not the most well-versed in Detroits, but it seems to me like they're talking about valves to cut off engine coolant/antifreeze flow to the heater core... doing this improves the effectiveness of air conditioning, as the blower motor, (AC) evaporator, and heater core are typically all housed in a single HVAC compartment. Such a valve causes the hot engine coolant to bypass the heater core, and keeps that heat out of the HVAC compartment. The difference is the AC blowing cooler.. not the difference between the AC blowing cold air and not blowing cold air at all.
AC refrigerant works through heat exchange... the refrigerant absorbs heat, becomes pressurized and superheated, then that heat exchanges to the ambient air which flows through the condenser fins, thus causing the refrigerant to rapidly lose heat and become 'cold'. Then that depressurized refrigerant flows back through the system, the blower motor blows air over the evaporator, etc. Your AC will be much more effective in, say, 85 degree weather than in 105 degree weather, as the higher difference in temperature between the superheated refrigerant and the ambient air allows for a more rapid and efficient heat exchange.
I don't know the full story here, but if the AC wasn't blowing cold air at all, I'd be willing to bet it was something more than a bypass valve. There are a multitude of things which could go wrong with an AC system, and the troubleshooting process is a bit of a PItA.

 

I have never had to mess with any Valves to get my AC to work properly.
Of course the oldest truck I have driven was a 2007 Volvo.

The one time the AC didn't work right...well...Something was broke.

 

Passenger side of the engine. You should see some hoses about the same size of a garden water hose running along the frame rail. My truck has 2 valves. One goes to the cab, the other to the sleeper. Close off both valves and that AC blows cold enough to frost the windows on the inside.

 

If you have to mess with the heater shut off valves they need to charge the AC.

 

My thoughts exactly!!!

 

They need to do a full system performance test. People automatically assume the refrigerant needs to be recharged always when, in fact, insufficient cooling can be caused by a number of things... blockage in the system, inadequate airflow across the condenser fins, saturated desiccant in the receiver-drier, excess refrigerant or PAG, etc. And if the refrigerant is low, there's a leak somewhere, and that needs to be isolated and fixed.