AC compressor size/capacity selection.

[JohnEd]

There is a recent post about AC pulley drive, etc.  In it Boogie relates how he fit a Sanden model 510 compressor to his engine.  510 means that the compressor has 5 cylinders and a total displacement of 10 cubic inches.  I think that is a rather large compressor and big impresses me as well as it does women.  In the discussion, Boogie says he charges the system till the hi pressure reads some 200 pounds or so.  I think the gist of that is that there is liquid freon in the hi side and the expansion valve is passing as much freon as it can.  Doesn't this mean that the compressor is creating liquid faster than the expansion valve can dissipate it?  Is there any benefit to increasing the volume of the hi side?

I want to run two air coolers, one in the front and one in the rear.  I don't exactly know what design criteria I should be addressing.  Nick said that 5 ton of capacity was in the average engine driven OTR ac system.  How many ton is the min with a well insulated,,,,say Pre?  What is the max?  Do I have to have both expansion units above the compressor?

I know that all the new cars and trucks are using that flat multi groove serpentine belt.  I think it is stronger and it uses less energy than the V belt.  Cheaper is not it's advantage.  Why are not more guys electing to upgrade the design of their system to serpentine belts?

Thanks,

John

[boogiethecat]

Hi John,
I can answer a few of the questions but I'll bet Nick can give you a lot more answers than I regarding tonnage and pressures etc.
Rather than delve deeply into it, I simply relied on the advice of a pro and didn't really question what he had to say.  It worked really well but I didn't end up much of a refrigeration expert...

The 510 compressor is actually somewhat small both physically and capacity-wise... and though my system is great for "on the road driving" it is actually not big enough, capacity-wise, to actually cool the driving section of my bus (roughly the front third, well insulated) on a 115 degree day.  But what I've found is (at least to me as the driver) that it's more important to have cool air blowing on your face than what the actual temperature of the cabin is, and the system does a good job of doing that. So I've never been unhappy with it.   But if I have more than one passenger, it's time to fire up Genny and turn on the roof air as well as I'm toodling down the road.

Regarding the serpentine belt, my guess as to why more people aren't using them is that they are a lot trickier to do right.  Vee belts can withstand a lot of misalignment and still operate happily... serpentines have to be spot-on or they trash themselves rapidly... then there is the issue of belt tensioning, which with a Vee belt is simply a "tighten and lock down" affair, whereas with serpentines you need a spring loaded idler to keep proper tension.  These issues along make it a lot more difficult to just toss one on and have it work, without a lot of precision...
and last, Vee belt pulleys are super available everywhere, but the selection of serpentine pulleys is somewhat limited to what you can find at a local auto scrapyard.  At least so far I havn't found a source of "general purpose" serpentine pulleys in various diameters and shaft sizes...

Ok, off to bed now
Cheers
gary

[luvrbus]

John, most buses use a 210 to 310cc compressor with a parallel flow condenser with fans to over come the length of the run in the hoses on a bus. Most people will make a sag in their line and add more oil to keep the system from dying the black death called by Ac folks ( metal particles in the system) so I am told.
Fwiw Red Dot makes a hydraulic powered compressor that fits nicely in the tire bay of a bus but very pricey.     good luck

[belfert]

My bus is newer and it does use a multi groove flat belt to drive the DN50.  The radiator fan and original A/C compressor use V belts.

I removed my DN50 to fix something and replaced the belt at the same time.  I must not have everything quite lined up right as there is slight wear on the edge of the belt.  I need to get out my straightedge and fix this at some point.

[Nick Badame Refrig/ACC]

Hi John,

If I were you, I would let a company like Red Dot size your system for you because if something is missized, you can easily

trash a compressor. Overcharging the systems high side will end up in overflooding the evaporator coil with liquid and forcing

liquid back to the compressor resulting in damaged pistons. Newer systems using R-134a need to be correctly charged because

of their higher operatering presures.  Any system utilizing expantion valves as metering devices can work with a sight glass.

A sight glass installed in the proper place in a system will give you a visual level of liquid in the high side for charging the system.

Hope this helps
Nick-

[Bob Belter]

Ahoy, John/Ed,  All,

On my -01 Eagle, I use two each A6 compressors.  Those are the big old cylindrical ones installed on GM cars in the '70's.  About 15 years ago when  I was laying out my system, I asked an A/C guy what was the best, and at that time, he said to use the A6, both for capacity, and because it has a lube pump installed in it.

THey work GREAT for me, and it is rare for me to need more than one system to be on while driving.

Nick my be willing to comment on how suitable they would be for selection today  -- obsolescence / availability / performance.

Enjoy  /s/  bob

[JohnEd]

Bob,

Thank you very much.  I wanted to go with the A6 a few years ago and was talked out of it by a few people that should know.  Seems they are out of production and the cars they came on are disappearing.  They seem to last forever so I think you are in good shape.  They will get pretty cheap in a while and then they will get very very expensive when they become rare.  My hunch.

I like the idea of two systems.  Your is one unit in the front for the driver and one in the rear.  Correct?

I might as well resign my self to that design as that is all that anybody is doing.

Thanks for your help Bob,

John

[Nick Badame Refrig/ACC]

Hi Bob & John,

I don't think the A-6 will go away any time soon.. It's only downfall is it's size. With smaller vehicles these days, the A-6 don't fit many engine conpartments.

It is still used in many heavy trucks and readily available from Polar bear inc. [my supplier]

http://www.polarbearinc.com/PBPC/Homepage/Search/Co/CO_Chevrolet.html

Good Luck
Nick-