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Vintage Truck Variable A/C

72crew on Fri May 20, 2011 9:04 PM User is offline

Year: 1972
Make: Dodge
Model: Crewcab Pickup
Engine Size: 413
Refrigerant Type: R134
Ambient Temp: Varies
Pressure Low: N/A
Pressure High: N/A
Country of Origin: United States


I'm retrofitting my vintage Dodge truck with air conditioning using stock underdash components. I want to get away from the stock idea of partially re-heating the air coming out of the evaporator to achieve temperature control. Why spend fuel and wear and tear on components to run the A/C full capacity just to heat it up again? I also want "set and forget it" temperature control as I've been spoiled by my Audi. I've been looking at using a variable displacement compressor along with a PWM temperature controller mounted in the cab to control the variable valve on the compressor externally. On this forum I've read that the signal required for the valve is a 400 Hz PWM signal (at least for the Sanden PXE) that draws a max .75A (not sure of the voltage). The controller I want to use can be seen here:

I've noticed that the clutch is eliminated on most of these variable compressors but I still want one as I won't be using the A/C most of the time. I'd also like to use a 3/8" v-belt to drive the unit. Since none of these modern compressors are likely to come with a v-belt clutch I'll have to put one on. I found that Delphi offers an externally variable unit with a clutch that can be seen here:

I was hoping that Delphi had retained some standardization on their input shafts so I can retrofit an earlier v-belt clutch unit that I can bolt on this unit, but I can't find any information on this. My other options are to machine the rib pulley adapt a v-belt sleeve over it or adapt my crankshaft to add a rib pulley (least desirable). Trying to locate a place to purchase one of these compressors has been difficult as I don't know what vehicles they were installed on and searching the Delphi P/N 7CVC185 doesn't yield any results. I have to fab a mount for the compressor anyway so how it was originally mounted is not a great concern. I plan on using a big multipass condenser for R134 and an appropriate dryer. The members on this forum seem quite knowledgeable and I was hoping I could find some answers to these questions:

Can anyone see any problems with this installation?
Which vehicles were these Delphi compressors installed on or might there be a better alternative?
Will a v-belt clutch fit on the Delphi or other compressor?
What voltage do these PWM control valves operate on? If it's not 12V I will adapt with resistors.
Is oil control going to be a problem running this compressor at reduced capacity?

Any information or opinions are welcome

Dougflas on Sat May 21, 2011 2:40 PM User is offline

I personally think you're trying to over design a vehicle AC system.

bohica2xo on Sun May 22, 2011 2:25 PM User is offline

Call Audi.

Order a reliable, one ton crew cab pickup truck.

I bet they can cover the one ton pickup end of it before they get "reliable" right.

Overcomplicated for an MVAC system. I am probably the biggest fan of variable displacement on this forum. But what you are planning is way beyond what is needed for MVAC. That dodge is a workhorse, not an economy car. I doubt is has sequential EFI, twin turbos & heated leather seats either. It is a truck. I like cold air in my trucks. I don't use the heater to temper things here in the desert, just the fan speed for temp control.

Keep it simple. Run a V7, and PWM the blower speed to adjust cabin air temp. The V7 can be swapped to a single V bely clutch - the site sponsor should be able to provide one. The V7 will destroke automatically if you reduce airflow over the evaporator. Since the cabin is always being heated, all you need to adjust is the cold air inflow. Simple.


"Among the many misdeeds of the British rule in India, history will look upon the act of depriving a whole nation of arms, as the blackest."
~ Mahatma Gandhi, Gandhi, An Autobiography, M. K. Gandhi, page 446.

72crew on Sun May 22, 2011 10:39 PM User is offline

Thank you for your replys,

I know I'm a newbe here and am in no way an automotive A/C expert, but I am a mechanical/control system engineer and a life long hot rodder. What I am proposing is a basic A/C system with the addition of PID closed loop temperature control and doesn't seem overcomplicated or over designed to me. My problem in implementing it is the lack of information on compressors presented to the general public. Seems to be on a need to know basis. I was hoping that this site, which seems to have alot of knowlegeable techs, would be some of those people that need to know. It really doesn't bother me that no one installs vintage systems with this feature - I want to. I'll share the results; maybe I'll start a new trend. If you have something specific as to why you think this is a bad idea, I'm all ears.

B- I considered the arrangement you propose but would rather have constant airflow over the evaporator for the stability of the control loop - and I like constant airflow - just at the right temperature ie the temp. required to maintain the controller setpoint. I live on the coast not the desert, but when I drive inland to visit clients the ambient temperature can rise 35 degrees and I would rather not be jacking around with the climate controls every 5 miles.

I'm almost done building the 413 now and yes it does have an Edelbrock programmable sequential EFI system, don't need the turbos and the heated seats in the Audi just make my balls sweat. I do appreciate the input but does anyone have answers to the questions I'm asking?


bohica2xo on Mon May 23, 2011 1:33 PM User is offline

You would be a fool to go that far into an engine, and not swap to serpentine drives if you want that compressor.

There will not be a V belt clutch for the CVC with electronic control - it has no clutch at all. The CVC 185 only shows as "validated" so it may not even be in production. The other variety of the CVC 185 is used on some cars:

CVC 185 compressor from AMA

The smaller displacement compressors may actually be on some cars - I would contact AMA by phone and ask.

Just because Delphi puts something on a webpage, does not mean they actually have any - I have run into this before with them.


"Among the many misdeeds of the British rule in India, history will look upon the act of depriving a whole nation of arms, as the blackest."
~ Mahatma Gandhi, Gandhi, An Autobiography, M. K. Gandhi, page 446.

ice-n-tropics on Mon May 23, 2011 2:50 PM User is offline

The latest fuel savings design is for an electronically externally controlled variable stroke swash plate compressor with a cycling clutch added. Even at minimum displacement, the clutchless compressor at 2% displacement plus the associated friction (in the winter) negatively affects the fuel efficiency. 2 years ago the Europeans were moving back to clutches, but I don't know the latest status.
I used a 400 hz PWM black box for bypass control for A/C service in Europe, but I don't have the details.

Isentropic Efficiency=Ratio of Theoretical Compression Energy/Actual Energy. How To Air Condition Your Hot Rod

Edited: Mon May 23, 2011 at 2:52 PM by ice-n-tropics

Vic on Sun April 17, 2016 5:20 PM User is offlineView users profile

This is specifically a question to ice n tropics, but anyone else with information, please chime in. I am interested in the 400 Hz PWM blackbox mentioned above. I've seen some items like this advertised on the net, but if you have a link to one that works, I would appreciate it. I specifically need a signal to control a Sanden PXE 16 compressor. I will be using this compressor for a non-AC purpose. I need a box that will take a 0 to 5 V DC input signal, and hopefully convert it to something that will control the compressor output proportionately.

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