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Old 11-11-2016, 11:46 AM   #1
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Adding road a/c to a rear engine bus?

Mornin' Everyone,

I am considering solutions for road a/c in a Bluebird 72 passenger RE bus.

On my last bus I relied on running the generator and typical RV roof a/c's. While driving in the Southwest I roasted. It was fine in moderate climates but 95F and bright sun was near unbearable.

I want to do better on this one. I want something that will keep me comfortable while I drive.

I have been looking at all sorts of electric a/c solutions that will likely require generator operation. Now I want to take a look at engine driven a/c.

The biggest challenge that I see is the 40 foot run from the engine to the drivers seat. I have no clue what the limitations are on refrigerant line length.

Another option would be to keep the evaporator at the rear of the bus and duct it up to the driver. Maybe run a duct the full length of the bus and place vents periodically along its length and have the last vent blowing directly on the driver?

Another variant would be an inverter connected to the coach charging system to run an electric a/c for the drivers area.

I know we have some a/c Guru's out there. What do you all think?

Thanks

S.
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Old 11-11-2016, 12:01 PM   #2
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No matter what you do, it is not going to be cheap. I do not know if there is a length restriction on A/C lines, but front to back on a full size RE bus would be pushing it. I would fear loosing too much pressure to the lines needing to be flexible.
I will throw out another crazy idea. What if you got an Automotive style A/C system from a place like Vintage Air, and powered it off of a small Honda GX gas engine, like you would see on a go-cart or rototiller. Honda Horizontal OHV Engine with Electric Start — 270cc, GX240 Series, 1in. x 3 31/64in. Shaft, Model# GX240UT2QAR2 | 241cc - 390cc Honda Horizontal Engines| Northern Tool + Equipment
Then you could find a place near the front of the bus and mount it. They do offer electric starters for them, so it could be started from the drivers seat. You could mount the engine under the bus at the front, add a larger fuel tank, maybe 5 gal and you got A/C.
So, a crazy idea, but it could work. Yoou would just need to find out the HP draw of a Sanden A/C compressor. I would guess less than 5hp.
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Old 11-11-2016, 12:43 PM   #3
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nope shou;dnert be any length restrictions on refrigerant lines... at least not 40 feet anyway... the Liquid line is the most critical and holds them ost refrigerant... if you are looking for multiple units we just have to locate your condensor in the spot that makes sense for both evaporators.. if you just want dash air then we want your condenser coil as close to the front od the bus as we can get it...

since oyu are converting and insulating we should be able to get you buy with one compressor / condenser and then up to 2 evaporators... I run such a setup in the DEV... custom built Dash air and rear unit...

yes its very pricey unless you find some take-off parts.. the condenser and evaporator are the priciest parts.. and then any fancy electronic controls you might want for temperature control.. paerts can be mixed and matched by brands, however the capacities must add up to be a close match..

compressor - Selttec 8390 / TM-16 (good for Max 50,000 BTU)couple hundred bucks.. brackets? can be pricey but likely find take-offs here or in a bus boneyard pretty cheap..

freon lines.. varies on how much you end up needing.. I used the slightly pricier Burga-Clip fittings because its a very simple leak free and still rotateable fitting once installed.. (i'll gladly loan out the Tool to crimp the fittings on)...

freon? my guess is about 10 lbs in a system on a full length bus iof the condenser is closer to the front...

vintageair and companies systems are typically only 9000 BTU and made for a car..

a typical full size FE / RE 12-14 row school bus with white roof and tinted windows will run 120,000 BTU of A/C... you dont need near that much since you arent looking to cool it in 3 minutes and there wont be 84 screamin demons aboard... and will be insulated...

horsepower calculations are out there for how much a compressor uses in a bus enviornment.. remember an auto environment is 9000- 12000 BTU and so those HP calculations are not what your compresor will pull in a bus..

-Christopher
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Old 11-11-2016, 01:20 PM   #4
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Cadillac can definitely tell you more on this subject than me or probably anyone else here...but...what I can add is that the lines for several mini-splits here at my studio were easily 40+ feet and functioned just fine. The only issues I can imagine are price and keeping the necessary lines well insulated along the length.
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Old 11-11-2016, 01:20 PM   #5
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I am getting ready to pull the condenser and evaporator (carrier) out of an E450 5 row. I wonder if I might re-task those pieces?

Perhaps mount the evaporator facing forward just aft of the drivers seat.

I did see some Thermo King APU's for $600-$900 for just the APU. No condenser or evaporator. Than would be a bit more flexible but I am back to running a second engine while running down the road.

Back to what you said Christopher, if I engine mount the compressor and run lines all of the way forward then mount the evaporator directly above the first baggage bay and place the condenser in the first (modified) baggage bay. That would place both pieces as far forward as I can and within about eight feet of each other.

Do I understand correctly then that I would need: compressor, receiver-dryer and expansion valve? Those would all live in the engine compartment?
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Old 11-11-2016, 01:50 PM   #6
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Quote:
Originally Posted by PNW_Steve View Post
I am getting ready to pull the condenser and evaporator (carrier) out of an E450 5 row. I wonder if I might re-task those pieces?

Perhaps mount the evaporator facing forward just aft of the drivers seat.

I did see some Thermo King APU's for $600-$900 for just the APU. No condenser or evaporator. Than would be a bit more flexible but I am back to running a second engine while running down the road.

Back to what you said Christopher, if I engine mount the compressor and run lines all of the way forward then mount the evaporator directly above the first baggage bay and place the condenser in the first (modified) baggage bay. That would place both pieces as far forward as I can and within about eight feet of each other.

Do I understand correctly then that I would need: compressor, receiver-dryer and expansion valve? Those would all live in the engine compartment?
the evaporator in your van should have a TxV valve built in depending on how they tied it into the factory dash A/C.. the receiver dryer you will want to buy brand new they should not be re-used.

your evaporator may have a freeze-thermostat built in, if not those are easy and cheap.. the dryer goes in the Liquid line between condenser and evaporator.. it can be near either.. the TxV expansion valve goes at the evaporator inlet...

what you want to do sounds very viable..
you can go as elaborate or as simple as you want on your temperature control..

the Trans/AIR in my bluebird has 2 fan speeds (resistor block) and 2 temperature settings.. cool and cold.. the cold setting keeps the coil temp at just above freezing.. the cool setting keeps the coil temp about 45 or so... both are simple mechanical tube thermostats mounted on the evaporator and wired to the driver control.. 45 coil temperature means it cycles the compressor when the coil temp reaches about 45 (usually means I get about 55 degree air out opf the vents)...

freon Lines.. you will have a line that goes from the compressor to the condenser inlet.. from the condenser outlet you go to the receiver dryer.. then from their to the evaporator inlet (TxV inlet)... then from the evaporator outlet you go back to the compressor...

most times on the receiver dryer theres a schraeder valve where you screw on a Trinary pressure switch that goes in series to the power for the compressor... if your freon leaks out it disables the compressot.. and also disables the compressor if the pressuer goes too high.. (fans quit or such)...


back to your E450 Van, if you plan to keep the dashboard A/C in it after removing the rear... it mah not have a condenser in front of the radiator... not all of the busses with rear units also have that front condenser.. a trip to the boneyard for a ford condenser and you can re-connect just your dash air in that Van... if you are lucky it already has one...
-Christopher
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Old 11-11-2016, 02:07 PM   #7
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This sounds simple enough to accomplish, even if a little pricey.... but would be worth it to have A/C going down the road.... and powering it from a smaller gas or diesel engine it would be operable even when the bus is not being driven (power the blower from the house batteries). With a large enough engine you could also drive a generator head so you could do double duty... and in the winter when you don't need the A/C just remove the belt that drives the compressor.
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Old 11-11-2016, 03:36 PM   #8
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Originally Posted by AlleyCat67 View Post
This sounds simple enough to accomplish, even if a little pricey.... but would be worth it to have A/C going down the road.... and powering it from a smaller gas or diesel engine it would be operable even when the bus is not being driven (power the blower from the house batteries). With a large enough engine you could also drive a generator head so you could do double duty... and in the winter when you don't need the A/C just remove the belt that drives the compressor.
compressors are on a magnetic clutch, the outer pulley spinning uses almost no resources... no need to yank the belt if you are running it with a genny engine. the indoor fan on mine pulls about 15-20 amps and the condenser fans pull about 30-35 or so..compressor clutch is like 5-10 amps i think..

-Christopher
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Old 11-11-2016, 06:04 PM   #9
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So.... what I would need to undertake this.....

- Evaporator
- Condenser
- Compressor
- Filter/Dryer
- Tubing to connect everything together
- Freon to charge the system
- Blowers and ductwork
- Switches and such to control the system

Did I miss anything?
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Old 11-11-2016, 08:23 PM   #10
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The Thermo King APU has a small (10hp?) diesel engine, an a/c compressor and a small alternator.

Take a look: Thermo King TriPac Auxiliary APU unit, 2014 model year NO RESERVE | eBay

The idea intrigues me but I think stuffing that into my bus may be a bigger project than I want to add to an already hefty to do list. We will see....
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Old 11-11-2016, 09:01 PM   #11
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Looks like that particular one is nonoperational but it does give another idea to consider.

Appreciate the info!
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Old 11-11-2016, 09:45 PM   #12
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I like this thread.
What's the best kind of tubing to use for the long runs on this project?
It needs to be flexible, and cheap would be nice.
Would hydraulic hose work?
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Old 11-11-2016, 09:49 PM   #13
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I like this thread.
What's the best kind of tubing to use for the long runs on this project?
It needs to be flexible, and cheap would be nice.
Would hydraulic hose work?
Not sure what the price per foot would be on this but it's an option to look at:

Industrial Refrigerant Hydraulic Hose | Gates Corporation
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Old 11-12-2016, 02:32 AM   #14
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What about using the red dot systems. mostly used in farm equipment and dump trucks. this is just one model.

New RedDot Mack Truck Backwall A/C Unit air conditioner Dump Truck R7830 | eBay
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Old 11-12-2016, 09:35 AM   #15
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you use standard Barrier A/C hose like in a car... it is designed to handle the elements.. each hose is a different size depending on the position and capacity.

APU's are great devices... expensive but awesome devices.. im not sure iof 10 HP is enough to spin an alternator and a compressor running 50k plus BTU of A/C or not but it would sure have a shot at it... most APU's are running only about 10k BTU or so for a semi-tractor..

I looked into repurposing a Reefer engine once.. they are diesel.. everything I found was craxy expensive if it ran..

you dont want ot use just 'any hose' as the size must be correct for putting for fittings on... again I recommend BurgaClip fittings because they are easy... I have my DEV bus down here in florida.. I'll try and go take some Pics of the various A/C components I used to give you an idea of what you need...

I'll be in ohio in a week or so where I have sopme spare hose and fittings in the garage where i can take pics of what the pieces look like before assembled..

the issues in types of hoses is not whether they will take the pressure but whether the Inside diameter matches the fitting, and also whether the refrigerant molecules will permeate through the walls of the hose... R-134A molecules are smaller than that of Hydraulic fluid..
-Christopher
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Old 11-12-2016, 03:09 PM   #16
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The hose I linked a few posts back was specifically engineered for long runs of refrigerant under high pressure, or that's how I read it anyway.... which probably means it's crazy expensive. I didn't dig too deep because I'm probably gonna do what was suggested earlier and rig a small engine (diesel would be ideal if it's not too expensive, but gas or propane would work too) to run a compressor and hang it somewhere underneath, near the front of the bus so long refrigerant runs won't be an issue. Will just have to come up with a gas tank arrangement that will hold enough to run it for an extended time when I'm on the road.

One advantage of using a diesel engine to run it would be that if you fill up your tank on the truck side of a truck stop you can use reefer fuel to fill the generator tank and not have to pay the fuel taxes on it. (It's the same fuel, just taxed differently.)
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Old 11-12-2016, 03:36 PM   #17
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I never knew they fueld REEFERS non tax.. since they are used on-road.. but it does make sense if only the engin e powering the wheels is necessary to pay tax.. of course then you have to maintain a separate tank for the Genny but the savings alone might be worth it..

just think about though the Horsepower requirements for a Bus A/C to work right..
for instance 5 tons (roughly 62000 BTU ) is about 17.5 kilowatts in calculation , up to 20 horsepower... all depends on how much you want to cool.. and as outdoor and indoor conditions change so does the amount of horsepower required to run the compressor... humidity, outdoor and indoor temperature all affect the compressor Load... do some good planning and calculations to go thast route and you wont end up under-powered..
-Christopher
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Old 11-12-2016, 03:40 PM   #18
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I think you may be right. I looked closer at the cooling capacity of the "stock" Thermo King APU. 12k Btu.

I am still intrigued by the idea of a small diesel that would run a good sized a/c compressor and alternator. Build a little Arduino based throttle controller to vary throttle depending on load. However, the simplicity of coach engine run a/c has strong merit as well.
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Old 11-12-2016, 03:52 PM   #19
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those APU's are designed for a semi-tractor sleeper cab and thats pretty much it.. many of them first generate DC and run the compressor off of DC power.. I know there are some that direct drive a compressor...

no need for special throttle control.. most generators use a very simplistic RPM controller to keep them at 1850 (I think it is) .. one of those type throttle controls would be fine... you dont change the system load by changing the RPM of the engine... most compressors will do their best to try and make up the differenceo n their own... load is changed by how much work is done on the refrigerant.. you always want a good supply of liquid at the TxV inlet.. the TxV will vary the refrigerant flow based on interior heat load... heat load includes humidity removal as well as heat removal... if the TxV goes to its minimum and the coil is in danger of freezing you have the freeze stat trip the compressor clutch out... then the comporessor will re-energize when the coil temp goes back up.. typically generator engine governors are good at responding quickly to load changes.. rarely if ever does a Genny engine take such a quick hit that it stalls.. the A/C compressor cycle in and out will change the engine load quickly.. of course a diesel is nice for this reason too as they typically have lots of torque at low RPM so are less affected by quick load changes..

-Christopher
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Old 11-12-2016, 04:05 PM   #20
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I never knew they fueld REEFERS non tax.. since they are used on-road.. but it does make sense if only the engin e powering the wheels is necessary to pay tax.. of course then you have to maintain a separate tank for the Genny but the savings alone might be worth it..
That's exactly how it works. I pulled a reefer trailer during my time with CR England, and truck fuel and trailer fuel were always separate for that reason. Only the fuel used to move the rig down the road is taxed. Fuel used for the reefer, APU, etc, is not taxed.

Quote:
Originally Posted by cadillackid View Post
just think about though the Horsepower requirements for a Bus A/C to work right..
for instance 5 tons (roughly 62000 BTU ) is about 17.5 kilowatts in calculation , up to 20 horsepower... all depends on how much you want to cool.. and as outdoor and indoor conditions change so does the amount of horsepower required to run the compressor... humidity, outdoor and indoor temperature all affect the compressor Load... do some good planning and calculations to go thast route and you wont end up under-powered..
-Christopher
This is still in the planning stages, so thanks for pointing this out. Guess I will have to look at the bigger 18-20 hp engines.

Quote:
Originally Posted by PNW_Steve View Post
I think you may be right. I looked closer at the cooling capacity of the "stock" Thermo King APU. 12k Btu.

I am still intrigued by the idea of a small diesel that would run a good sized a/c compressor and alternator. Build a little Arduino based throttle controller to vary throttle depending on load. However, the simplicity of coach engine run a/c has strong merit as well.
Running it off the bus engine is obviously the simplest option, BUT.... that removes the option of running it while the bus is not moving. You have to idle the bus engine to cool it... a diesel engine that size burns about 1 gallon of fuel PER HOUR at idle. More if you use the fast idle. If you're only planning to use it while on the road this would be acceptable.

A smaller diesel will be much more frugal on fuel.... I don't have hard figures but I figure a gallon will run it 3-4 hours at a guess. Look up a diesel powered generator with the size engine you're looking at and the listed runtime at 50% load will give you a good baseline.

When I was in the military on the honor guard the bus we used had a diesel engine with a separate 3 cylinder diesel engine powering an A/C system. That sucker was loud but it didn't matter in that application. Going down the road or boondocking with no one else close by it wouldn't be an issue but in a campground it might be, so you'd want to find one that runs fairly quietly, and have electric A/C as backup.
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