> Subject: Re: GMC: A.C. Compressor (trivia)
>
>
> Bravo!
Thanks, and I agree, every day adds to my knowledge base.
> Mark, this is the kind of post that keeps me looking forward to reading my
> email every day. It is a poor day that I can't learn something.
> Some of that
> I knew...like the STV/POA...but a heckuva bunch I didn't...like
> the reverse
> rotation A-6. I didn't realize there was such a thing or that a Corvair
> would use it. I guess the only difference would be the oil
> pump...the swash
> plate and pistons wouldn't care which way they were turned.
You're right. Oil pickup and control are the issues solved by the green
compressor.
The condenser mounts over the (horizontal) fan in this application.
It's a lovely brute force design, one of GM's finest.
> Since you obviously DO know your butt from the North Star,
> perhaps you could
> volunteer an opinion on how big an evaporator the A-6 and stock condenser
> could support to cool the rear while underway?
The A-6 is almost unlimited in capacity, but it can suck a lot of power.
The rule of thumb (for R-12) is usually 25% more condenser than evaporator.
R-134 takes more, up to 50% I'm told. With that said, I know that the A-6
supported 3 evaps in many Cads.
I don't have the measurements for the stock condenser, but it should easily
support multiple evaps. Caddy put them under solenoid control in the 60/80
special series. (that is, they 'switched' them "on and off" with an evap
mounted thermostat. Also a very common technique in ambulances. Evaps are
wired to a common bus to control the compressor clutch.
> I have dreamed of building an "integrated" system that would use one large
> condenser, the dash evaporator and a rear evaporator, and two
> compressors...the A-6 that is engine mounted and parallel it with
> a hermetic
> electric. Each compressor's check valves would keep it from being
> a problem
> when the other was running. You'd have to have a large electric
> fan to cool
> the condenser when running on 120 volts. But this would get rid
> of the need
> for the noisy protruberances on the roof.
One issue would be oil control, the A-6's can almost pump themselves dry
when the start, then re-capture the oil after stabilized running. Hermetics
are more stable and seldom throw oil in the high side output. Two
compressors may create some unusual oil distribution patterns.
My first thought is that we need to find out is what size the hermetic would
need to be to get the job done. I'd guess very large to support the size of
the evap orifices that the A-6 likes.
I used to have a book that gave the capacity of the A-6 at various RPMs. I
can't find it right now. I think it was an obscenely high number, like 12+
tons at cruise speed. My concern is that the compressor would not generate
enough head pressure to condense the refrigerant. Particularly if the
expansion valve couldn't refine its metering enough.
Then, my second thought is that this doesn't matter, the capacity of the
system would simply be set by the compressor, period. Less capacity is
required by the occupants when stationary due to less heat gain. After all,
two 12-15K (or even one, for that matter) duo-therms do the job now.
> Perhaps the condenser for this arrangement could be somewhere besides in
> front of the radiator, though I don't see why the present
> location wouldn't
> be just fine.
>
> Any thoughts on this?
My next thoughts are that the compressor required would take some serious
electrical power.
Perhaps some additional research is in order. This is a novel idea worth
pursuing.
Mark
>
>
> Bravo!
Thanks, and I agree, every day adds to my knowledge base.
> Mark, this is the kind of post that keeps me looking forward to reading my
> email every day. It is a poor day that I can't learn something.
> Some of that
> I knew...like the STV/POA...but a heckuva bunch I didn't...like
> the reverse
> rotation A-6. I didn't realize there was such a thing or that a Corvair
> would use it. I guess the only difference would be the oil
> pump...the swash
> plate and pistons wouldn't care which way they were turned.
You're right. Oil pickup and control are the issues solved by the green
compressor.
The condenser mounts over the (horizontal) fan in this application.
It's a lovely brute force design, one of GM's finest.
> Since you obviously DO know your butt from the North Star,
> perhaps you could
> volunteer an opinion on how big an evaporator the A-6 and stock condenser
> could support to cool the rear while underway?
The A-6 is almost unlimited in capacity, but it can suck a lot of power.
The rule of thumb (for R-12) is usually 25% more condenser than evaporator.
R-134 takes more, up to 50% I'm told. With that said, I know that the A-6
supported 3 evaps in many Cads.
I don't have the measurements for the stock condenser, but it should easily
support multiple evaps. Caddy put them under solenoid control in the 60/80
special series. (that is, they 'switched' them "on and off" with an evap
mounted thermostat. Also a very common technique in ambulances. Evaps are
wired to a common bus to control the compressor clutch.
> I have dreamed of building an "integrated" system that would use one large
> condenser, the dash evaporator and a rear evaporator, and two
> compressors...the A-6 that is engine mounted and parallel it with
> a hermetic
> electric. Each compressor's check valves would keep it from being
> a problem
> when the other was running. You'd have to have a large electric
> fan to cool
> the condenser when running on 120 volts. But this would get rid
> of the need
> for the noisy protruberances on the roof.
One issue would be oil control, the A-6's can almost pump themselves dry
when the start, then re-capture the oil after stabilized running. Hermetics
are more stable and seldom throw oil in the high side output. Two
compressors may create some unusual oil distribution patterns.
My first thought is that we need to find out is what size the hermetic would
need to be to get the job done. I'd guess very large to support the size of
the evap orifices that the A-6 likes.
I used to have a book that gave the capacity of the A-6 at various RPMs. I
can't find it right now. I think it was an obscenely high number, like 12+
tons at cruise speed. My concern is that the compressor would not generate
enough head pressure to condense the refrigerant. Particularly if the
expansion valve couldn't refine its metering enough.
Then, my second thought is that this doesn't matter, the capacity of the
system would simply be set by the compressor, period. Less capacity is
required by the occupants when stationary due to less heat gain. After all,
two 12-15K (or even one, for that matter) duo-therms do the job now.
> Perhaps the condenser for this arrangement could be somewhere besides in
> front of the radiator, though I don't see why the present
> location wouldn't
> be just fine.
>
> Any thoughts on this?
My next thoughts are that the compressor required would take some serious
electrical power.
Perhaps some additional research is in order. This is a novel idea worth
pursuing.
Mark
