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Old 07-06-2016, 08:34 PM   #1
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Join Date: May 2015
Location: Oklahoma aka "God's blind spot"
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Year: 1989
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Chassis: 35' Retired Air Force Ambulance
Engine: DT466, MT643
Rated Cap: 6 souls and a driver
Air Conditioner question






1988 Retired Air Force Ambulance with dedicated Mitsubishi Diesel engine turning two R-12 air conditioner compressors.... Ducted air tunnels down each side. One compressor is dedicated to each side.
(Engine is 35 hp running 3600 rpm)
Problem: one compressor locked up and whole unit is low on freon and cycling the driver's side a/c compressor/condenser on and off. Passenger side is not cycling at all because it's compressor has no belt to engine pulley. (Fortunately, it's the outboard compressor that's gone bad, not the inboard)

Should I
1) least desirable option: replace the locked up compressor myself, have an hvac tech vacuum system down and refill with R-12 ( ID plate shows 12 pound system) (hearing that R-12 is hitting around $1200 for 30# can)

2) less desirable option: replace compressor, vacuum down, and refill with "Freeze 12" or R-134a (I keep hearing from ASE Certified Auto Tech instructor that this will not produce optimal results)

3) most favorable option: pull both A/C compressors, get on Craigslist and find a generator with bad motor (found 2 locally for $100 & $50) I could actually mount 2 generators to this configuration)
Pull the generator head, attach a v-belt pulley to shaft, build the brackets to mount the generator to engine. (Or Direct shaft coupling)
Buy 2 rooftop mount Motorhome 13,500 to 15,000 A/C units, mount them in roof and use the abandoned freon lines as conduit to wire the units to generator or sub panel breaker box. (Which will in turn connect to RV Campsites when generator is off)

4) less favorable option: same as Option 3 but use 2 mini-split units but gain heating ability.

Need some help with Pros & Cons... I'm concerned with chasing the R-12 freon rabbit this time and having to chase it again when the other compressor gives up.
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Old 07-06-2016, 09:01 PM   #2
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Option 3 sounds like a complicated solution to the problem. Option 1, sticking with R12 is an expensive solution. Option 2 will likely be your least expensive choice, doing a complete R134 swap will be cheaper than a couple cans of R12 (and future refills will be easy enough to manage).
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Old 07-06-2016, 09:11 PM   #3
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Quote:
Originally Posted by Brad_SwiftFur View Post
Option 3 sounds like a complicated solution to the problem. Option 1, sticking with R12 is an expensive solution. Option 2 will likely be your least expensive choice, doing a complete R134 swap will be cheaper than a couple cans of R12 (and future refills will be easy enough to manage).
But with staying with the current configuration, I do not have AC Voltage to run appliances.

I will need to purchase a generator if I don't swap.

I neglected to mention that in my write-up
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Old 07-06-2016, 09:16 PM   #4
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Quote:
Originally Posted by milkmania View Post
But with staying with the current configuration, I do not have AC Voltage to run appliances.

I will need to purchase a generator if I don't swap.

I neglected to mention that in my write-up
Maybe a little complex, but:
Insulate the bus.
Fix up one A/C system which should do for the whole insulated bus.
Repurpose the other into a genset.
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Old 07-06-2016, 09:51 PM   #5
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something doesnt sound kosher... one compressor is "locked up" but still cycles in and out on low freon? if its locked up it wont cycle.. it would burn off the belt...

the outboard compressor missing the belt may very well be Locked up.. or had a bad freon leak so they removed the belt...

R-12 to drop-in or R-134a is possible on these... those Look like TM-21 style compressors though id love to see the part numbers on them...

you can use a generator engine for an A/C compressor however its a bit of work to connect up...

the part about locked up and cycling has me baffled though..

-Christopher
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Old 07-06-2016, 10:14 PM   #6
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Join Date: May 2015
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Engine: DT466, MT643
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Quote:
Originally Posted by cadillackid View Post
something doesnt sound kosher... one compressor is "locked up" but still cycles in and out on low freon? if its locked up it wont cycle.. it would burn off the belt...

the outboard compressor missing the belt may very well be Locked up.. or had a bad freon leak so they removed the belt...

R-12 to drop-in or R-134a is possible on these... those Look like TM-21 style compressors though id love to see the part numbers on them...

you can use a generator engine for an A/C compressor however its a bit of work to connect up...

the part about locked up and cycling has me baffled though..

-Christopher
Raised lettering on the compressors say "510811" and when I googled it, there was a lot that came up referring to "ELSTOCK 51-0811"... But I didn't see many pics that looked like mine.

When I say the driver's side condenser/compressor runs... It blows cool'ish air, and cycles on and off several times every 2 minutes, sporadically.
There is a thermostat dial above the driver's seat that I can rotate, and when I rotate to above air temp, the blower & condenser shut off.

The belt is missing from the outboard compressor, and the internal part of pulley will not spin by hand. The external pulley/v-belt groove will spin.


This is a ScottAir system
Model # 75 K ____ D (underscore = space)
Serial #809310055
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Old 07-06-2016, 10:41 PM   #7
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that compressor looks like a standard Sanden / Selltec ear mount top discharge compressor...

very similar to the one i just installed (I added road A/C to my bus)...

Compressor - 05 000 200

new compressors can be ordered pre-charged with oil or dry... if you switch to R-134A.. use POE oil as itwont cause issues with the R-12 mineral oil...

as long as that old compressor didnt black death...

if your fittings are different size on the new vs old compressor thats fairly easy fix... making new A/C hoses is a snap now with BurgaClip fittings... and they make a fitting size and angle for about everything out there....

near the condensors will be receiver dryers.. always replace those when replacing compressors or changing from one type of refrigerant to another... we can find those pretty easy too...

you can get different clutch pulley sizes depending on the RPM of the engine driving them and the pulley ratio... thus to drive the compressor at the proper RPM and not over rev it or under-rev it.. since you have a dedicated engine for the A/C im guessing it has a set RPM... you can measure the circumferance and diameter of the existing clutch pulley to get an idea what size you need to replace it...

ive been rebuilding A/C for years and this doesnt look out of the ordinary to me..

-Christopher
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Old 07-06-2016, 10:50 PM   #8
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Quote:
Originally Posted by milkmania View Post
But with staying with the current configuration, I do not have AC Voltage to run appliances.

I will need to purchase a generator if I don't swap.

I neglected to mention that in my write-up
I suppose it depends how much AC power you'll need. An inverter can be used for light loads ... if you leave the existing A/C systems in place, how much electrical load will you need? Refrigerator? Microwave? Other cooking? Other 120V items?

You might find a smaller generator will suffice with not needing to power large rooftop AC's ... and here's the thing ... if you are trying to use 2 smaller generators powered from the diesel engine (belt driven), you'll probably need to keep the circuits completely independent of one another ... otherwise your AC could be "out of phase" and potentially dangerous. At what point does this become more economical than simply using the diesel for cooling and a smaller gen or inverter for the remaining electricals?
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Old 07-06-2016, 10:57 PM   #9
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Join Date: May 2009
Location: Columbus Ohio
Posts: 7,949
Year: 1991
Coachwork: Carpenter
Chassis: International S3800
Engine: DT360
Rated Cap: 7 Row Handicap
for electricity... unless you are running a crapload of stuff.. id say set up a couple batteries, a 1500 watt inverter and install a Bosch SB-200 School bus alternator on the mitsi engine... it looks big enough to handle quite a bit of load...

the SB-200 is designed to put out a bunch of power at Low RPM's and is easily outfitted with a V-belt pulley (mine is)...

you use the mitsi engne for the A/C and as a generator... 1500 watts is quite a bit of electricity if you arent using it for cooling or heating appliances....

-Christopher
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