Vintage Air colder when sitting still

[CSG]

Hey guys, looking for some ideas on where I should be looking. I have a 67 C10, 5.3 LS, with a Vintage Air kit. At this time I have not checked any pressures. I did not install the air either so I don't know anything about how the install was done. What puzzles me is that the air out of the vents is colder when I am sitting still than when the truck is moving. This is backwards of anything I have had before. It has always done this but was not an issue until the extremely hot temps. we are currently having. Anyone that can explain this to me?

[dontlifttoshift]

Compressor moves more refrigerant and consequently the system has more pressure which gets better atomization after the expansion valve when the rpms come up. I will always get colder vent temps at 1500 rpm than at idle.

That is why late models use variable vane compressors. They are always moving the correct amount of refrigerant through the system to maintain vent temps.

[dhutton]

Maybe it is overcharged and the pressure is too high and the binary switch is shutting off the compressor.

Proper diagnosis requires putting some gauges on it.

Don

[TheJDMan]

Is it possible that an air blend door is open allowing hot air to mix with the cold air as the vehicle is moving?

[CSG]

I don’t “think “ the compressor is cutting off as the air remains pretty cool constantly just not as cold. On the air blend door I don’t know. There is a manual block valve in the heater hose though that is currently closed. I need to put gauges on it and report back.

- - - Updated - - -

I don’t “think “ the compressor is cutting off as the air remains pretty cool constantly just not as cold. On the air blend door I don’t know. There is a manual block valve in the heater hose though that is currently closed. I need to put gauges on it and report back.

[btmatt]

Pusher fan restricting flow at speed?

Lack of vents on the shroud restricting flow?

[CSG]

Puller fans only. No vents on shroud. The engine runs a bit cooler at speed but the ac is the opposite,

[dontlifttoshift]

Compressor moves more refrigerant and consequently the system has more pressure which gets better atomization after the expansion valve when the rpms come up. I will always get colder vent temps at 1500 rpm than at idle.

That is why late models use variable vane compressors. They are always moving the correct amount of refrigerant through the system to maintain vent temps.

CSG, I'm an idiot. I read your post several times and still understood the exact opposite of what you were saying. I am much more interested in pressures at idle and at cruise RPM now.

[CSG]

No problem, I thought maybe I was not understanding what you were saying…

[TheBandit]

What happens if the vehicle is stationary with the engine RPM raised? Do you see reduced performance or is it only reduced performance when the vehicle is physically moving?

I'll second the blend door and also if the system has a heater core bypass/shutoff valve, it may be allowing more coolant into the heater core at higher engine speeds. If the AC clutch is cycling, you may have an overcharge situation. If the amount of air coming out of the vents is decreasing, you might be icing up the evaporator which could be a charge issue. AC pressures are going to tell you a lot if you can get a set of gauges on it.

[CSG]

I have not tried raising rpm while stopped. I will check that as well. I have gauges to use, life has been giving me a hard time so I haven’t been able to mess with it but hopefully I can get on track shortly. I’ll try revving at a stop on the way home but I don’t have a thermometer with me so I may not be able to tell a difference

[Smee78]

I am curious to see what the gauges say. It does sound like a possible overpressure problem.