Most unique air conditioning in a CUCV

[Keith_J]

FINALLY finished the project started in 2012, AC for my 1031. Basically, a large 24 volt DC motor is driving a Sanden SD7B10 compressor direct drive. The condenser is mounted conventionally, using the engine cooling fan and the evaporator is a small under dash unit. Aside from 2 holes in the frame rail and the holes for the refrigerant lines, there is little modification to the vehicle.

Yes, you CAN see the load on the voltmeter, it stays in the 12.8 volt range when on, the compressor cycles based on evap temp alone. I guess it is a few ounces shy so it gets pretty cold at the EX valve which is where the thermostat resides.

There is some belt squeal at low RPM, the engine needs new belts. I'm running dual purpose 27 marine/cranking batts so they can tolerate the cycling but an additional voltage cutout for the AC would be wise as to not run the voltage into the red.

Here is the compressor-motor. Yes, that is a Lovejoy type coupling. I took the compressor clutch apart, using only the hub. The rivet holes were then used to drill a mating pattern on the half of the coupling, then these were threaded 1/4-24 TPI and the hub was bolted to the coupling half.

 

[Skinny]

I dig it!

Specs on the motor and did you run an ammeter on it to see what the draw is?

 

[Keith_J]

Motor is an Imperial Electric 24 volt 70 amp nominal draw NEMA 56 like size brushed PM DC cont duty 3000 RPM 2.25 HP that I picked up from a surplus retailer. The alternative energy guys depleted the stock so no more.

I don't have a shunt to measure current but estimate something in the 80+ amp draw right after startup, it depresses voltage to 25 V and makes belts squeal. IMHO, the alternator leads to batteries are a bit weak for 100 A, paralleling with some #4 might help. But I first need to address the charge level.

Unlike engine driven AC, this unit does not require high pressure cutoff because it is constant RPM. Or, the speed won't ever get above 3000 RPM. That is right in the heart of the compressor's peak CoP, coefficient of performance of 2. That means for every watt of mechanical power (1 newton-meter second), it moves 2 watts of heat. Under certain conditions...YMMV yada yada engineering lingo... But I should have a low pressure switch, just to protect the compressor in case it loses charge. No biggie, this is all a prototype. The unit cycles based on evaporator temperature and since it is cycling at max cool, that is a sign of slight under charge. I have a few weeks to iron that out. Plus I winged a deal on refrigerant 134a for $6 per 12 ounce can using my MVPA credentials .

I AM the club's mechanic, driving the mechanic's truck.

Other features include 150 ampere circuit protection, keyed master switch, blower operating off the back battery (balances load) and I forgot to plumb for the condensate drain . So, more work ahead.

 

[Speddmon]

WOW...$6.00 for 12 Oz.

A few months ago I picked up a new 30# bottle at the local Rural King for $69.99.


Nice work on the A/C. I like it. Where did you mount the compressor/motor? I would like to see some pics of the install, it sounds neat.

 

[Keith_J]

Yes, I am a regular at this auto parts store and a little bit of honey got me the business account discount. Did the same with the group 27 dual purpose marine batteries in this CUCV. $80 out the door for batts with 850 CCA and 180 RC. Dual purpose deep cycle and cranking, because of the AC motor.

The motor+compressor is mounted to the outboard side of the right frame rail, underneath the cab. Along with the contactor (relay) and the keyed switch. The circuit breaker is on the firewall underneath the negative bus. Both + and - 24 volt cables go to the main bus terminals, all #2 wire.

Further testing will be done with an optical tachometer, borrowed from my RC airplane tool box. I would think two strategically placed aluminum foil tape squares on the Lovejoy type coupling would mimic a 2 blade prop so I could measure speed (RPM). I have two type K thermocouples but in reality, manifold gauge is all one needs...OK, evap temp is a factor. So the type K will be used.

We have had a brutal winter, for Central Texas. We have a donkey who sprouted a THICK coat of wool last fall, it is showing no signs of turning loose so the better half is claiming we have more cold weather. I mentioned it is certain since my CUCV now has AC.

 

[Keith_J]

Ok, $6.04 per can, with tax. I give them plenty of business.

But now I see weepage from charge ports. So I either pay a pro to recover 24 ounces of R134a and swap the Schraeder valves or ignore it, then DIY and evacuate with $18 recharge. The Clean Air Act amendments are so arcane they don't make sense.

 

[davo727]

Cool, Im just thinking you could gear it down. shouldn't it only need to turn 1000 rpm at most ? That would drop your starting and run load.

 

[patracy]

I'd like to add AC to my CUCV one day. (I've got most of the parts to do it now actually) But I want to keep it setup for 24V. And since I have a turbo, it'll be an interesting means to do it. I was kinda thinking of a different path. I was thinking about just using a single alternator, then a vanner battery equalizer like I have on the SEMTT. That'd free up the second alternator slot. And since the only thing on my truck that still uses 24v is the starter, it wouldn't be too difficult for the second battery to rebound in that setup.

 

[Keith_J]

Yes, you could go with a battery equalizer to maintain 24 volt starting. With good batteries, you would have enough to jump start too. But still that 100 amp, 24 volt charging system makes jump starting just a bit better. I know, I have had to start timo247's 1009 a dozen times the last few weeks due to failing batteries. I watch the voltmeter during the process.

He is step son #4 and drives it to high school. We just got some group 31s today so no more rescue..HOPEFULLY.

I need to order a few alternator rebuild kits. Just in case seeing how I have 4 of those beasts, 2 of them will be intensely operated.

 

[mahdey]

Ok, $6.04 per can, with tax. I give them plenty of business.

But now I see weepage from charge ports. So I either pay a pro to recover 24 ounces of R134a and swap the Schraeder valves or ignore it, then DIY and evacuate with $18 recharge. The Clean Air Act amendments are so arcane they don't make sense.

they make a tool where you can replace schreader valves on AC without having to recover and recharge. I think I got mine from snap-on...

 

[Keith_J]

I know about those tools. Unfortunately, the location and space of the compressor-motor and the charge/test fittings prevents that, unless I dismount the compressor-motor.

$18 is too cheap. If the caps don't seal.

 

[Keith_J]

Topped off the system today to proper pressure levels, now it produces condensate and cools adequately for hot days. The motor is a 3000 RPM rated unit, I measured 2950 RPM under full load. That is right in the heart of the compressor's peak thermodynamic efficiency.

Now I need to fix weatherstrip on the doors to keep that cool, drier air in the cab. And new, aggressive belts to prevent slippage since the alternators are getting a good workout.

No idea of current. When the compressor is on, the voltmeter drops from mid-green to mid-yellow, meaning 28.9 to 25 volts. On the road, it cycles on for 30 seconds and off for 45 seconds which helps recharge the battery surface voltage.

Somehow, by chance I suppose, the charge/test port valves are now SEALING!!! Could have been a bit of dust/hair, hopefully it will not wreck the compressor. Anyhow, on the first test drive, the evaporator is producing a LOT of condensate. And while the tubes are there, they only vent to the door sills. I need to buckle up and drill one more hole in my precious M1031.

 

[Keith_J]

The high pressure cap didn't seal, it blew out the seal last weekend. So I broke down and bought a kit containing new valves, the tool and two caps. Figured I would try to tighten the valves, just in case...AND IT WORKED!! Also found the can tap that works with my manifold gauge set so I could top it off PROPERLY with two gauges. That is when I discovered another problem..airflow through the condenser was insufficient. I couldn't get evap temps high enough to prevent icing without high side in the 240 PSI range. Or higher.

I made baffles to force most of the fan flow through the evaporator and then diffuse it to the entire radiator. This was the magic trick, now evap temps are in the 29 F range with condenser temp in the 130 F range. For a 75 degree day of testing, it is perfect. Air blows out at 36 F on high speed and coldest setting on the thermostat. Yes, it still cycles to keep from icing, that is a must.

I rebuilt the alternators last weekend since they were having problems swinging a 30 amp load (coffee pot run off a 24 volt inverter) and keeping system voltage above 24. That worked great but I wanted to see how great they are. I have a 0.001 ohm shunt, placed in series with a load, current through the shunt in amps equals voltage drop in millivolts. So I hooked it to the right alternator output and ran the air conditioner. 115 amperes on motor start, dropping to 75 quickly and then stabilizing around 60. So I am putting a good load on the alternators, no wonder the AC dims the lights.

With that, I might have to incorporate a pulse width modulated speed control for the AC motor, that would reduce speed (and power consumption) without much reduction in torque. Sure, it would reduce some refrigeration capacity but it would decrease voltage depression. Either that or convert to LED headlights.

 

[tim292stro]

I've been following your setup, I'm planning on doing something similar for my XM1027 project, but without rolling my own compressor drive.

Any idea how many BTU your setup is supporting?

I'm thinking of going with a MasterFlux DC compressor setup (also R134a), the model I'm looking at will do around 15k-BTU depending on the voltages you can feed to it, and I'm planning two of them with a 24V RedDot HMMWV condenser on the roof. The controllers take a 0-5V input for "throttle", and with the appropriate check valves and main controller, I should be able to do from 4k-30kBTU.

 

[Keith_J]

I'm getting about 16,000 BTU/hour off mine. Compressor is in the peak efficiency range and condenser is oversized with very good airflow. This is based on calculations I did this morning using 400 cubic feet per minute and temperature drop of about 35 degrees.

I see ~3000 watts of cooling off one of those Masterflux compressors, one ton is 12,000 BTU/hour which is about 3500 Watts. With two, you should be in the 6000 watt range which is 1.7 tons or about 20,000 BTU/hour. It won't feel ice cold down here in TX but will dehumidify and should be fine for your latitude.

You will be fine on power consumption as those brushless DC permanent magnet motors are very efficient.

 

[tim292stro]

My truck will also have more insulation than your average CUCV: Laminated windows, floor and pillar/ceiling insulation blankets, with lots of insulation around the entire exhaust under the truck. I figure that'll help a bunch. My aunt works for Carrier, and she's offered some help with the design and commissioning. Ideally I'd like to see 2-tons of cooling for high-altitude de-rating, I go up Highway 108 into Nevada past the Marines Mountain Warefare training center a few times a year, they are roughly at 10,000-feet. That's rough on the engine cooling system too (thus the roof-mount RedDot condenser out of the engine air stream).

 

[Keith_J]

Back to the future..the AC developed a leak in the high pressure hose so that will need to be replaced. So I have time to upgrade..first will be converting from a cycling system to a variable speed compressor. Why? Automotive AC compressors are designed to run at varying speeds which varies the suction pressure based on heat load and speed. My setup is constant speed which leads to pressure issues and probably causing the leak.

So I found a 100 amp pulse width modulating speed control unit for about 100 US doll hairs..and add in a 55,000 uF capacitor and this should work. What this does is "chop" the current into pulses, varying the amount of time the current is on to vary the speed. Very efficient means of speed control and it doesn't limit torque. This will put the motor in a more electrically efficient RPM and run with more refrigerant. Brush type motors have most torque at stall and the least torque at max speed.

https://www.amazon.com/dp/B07JMG6N7T/?coliid=I1MCXSD7QYA6ZS&colid=3TZV91R6OS8BJ&psc=0

The capacitor? It will help smooth the motor controller draw.

Now I just need to find the time to do these upgrades! Working nights isn't bad, working 11s is!

 

[Keith_J]

Got the speed controller..well built especially considering the origin. No documentation with the unit, I had to figure it out on my own.

First is the testing. I hooked a 7506 single filament brake light bulb to the output, then used an 18 volt Ryobi tool battery to drive the motor speed control, its rated for 10 to 50 volts and up to 100 amps continuous and up to 200 amps peak. I hooked a voltmeter over the bulb to measure voltage. Sure enough, it worked as a dimmer control but at what I considered a safe brightness, voltage was only 6.2. That is the magic of pulse width modulation, it acts like a DC transformer. When the transistors are conducting, the light bulb is getting 18 volts. This is only for about 48 milliseconds. When the transistors are off, the light bulb is getting no voltage so it cools off. The transistors are off for about 16 milliseconds. This is how pulse width modulation works, it allows full voltage so the motor has full torque but the speed is a function of pulse width.

I verified this is a 15 kHz pulse frequency, 15.64 kHz to be precise. Shouldn't pose any RF issues, thats in the low AM band. Its well protected in a Faraday cage. I am stoked, just need to find some silver terminals to connect what looks like a 3mm screw to 4 AWG wire. Don't want to lose any power here.

I will mount this unit in the cab as it has no protection.

 

[Keith_J]

Its back alive! It wasn't the hose, it was a hard aluminum line. Vibration against the cab mount wore a hole in it. GTAW to the rescue, then a flush+lube change and dryer swap. It held 150 PSI argon so pulled a hard vacuum and charged.

I also baffled the condenser and radiator with foam seal between the condenser and radiator. ALL air flows through the condenser. Lovely cool. No more swamp butt.

Next is the variable speed. Just undecided on where to mount and how many holes to drill.

I had installed a digital volt-ammeter on the left alternator negative to ground lead. Maximum I saw was 90 amperes 1500 RPM. So I know it taxes the alternators very high.

 

[Keith_J]

30 minute 60 mph run at night..set thermostat to highest temperature. Cycles on for 30 seconds, off for a minute. Saw 101 amperes on the alternators. That includes 12 amps for low beam lights plus 5 for running lights. 4 amps for fuel cutoff and rest is compressor.
Voltage never dropped below 25.5 which means these 27SI alternators are skookum choochers.

But constant running at 100% rated output causes lots of heat. The voltage regulators are temperature compensated to protect batteries, assuming alt temp is battery. Hot batteries off gas at lower voltage.