With all the creativity housed on this board, I thought that I should throw out my question for you all to chew on. Here's the deal: The bus does not have enough A/C. It has a rear Transicold EM14 evaporator married right up to the factory in-dash evaporator. GM Stock compressor. Stat's don't look good on capacities. The stock compressor has it's hands full with the front evaporator, let alone a huge back evaporator on top.

After speaking with the designer of the bus, Carrier Transicold, we all seem to have come up same idea . . . not enough compressor to go around. It has a skirt mount Carrier CM2 dual fan condensor. It's got enough condensor, just not enough compressor. The HT6 (stock) is about one of the largest out there. The A6 is bigger, but seem to be having fun finding one that may fit.

There is a company out there in Texas, some of you may have heard of that state before ;), that make special brackets for engine driven compressors. This would be a second compressor on the system, to split out the rear and front systems. Problem being, it's 'bout $300 for the kit, which is the mount and belt only, no compressor. So, after compressor, another condensor coil, and bracket, we are over budget on our improving the air conditioning system on the bus.

So, I was wondering if anyone out there may have any suggestions as to what I may be able to do next. I've have fiddled with this setup too long, and improved it as much as possible, but it still isn't enough.

I might get stomped for this but I've used HC12 or Dura Cool, in the states as far as I can tell the EPA does not like it because it is not made by Dupont. this stuff has a much lower head pressure and runs as cold as R12 and it is a complete drop in refridgerant(sp?) You just evacuate the R134A and replace it with HC12, one 6oz can of HC12 is equal to 1lb of R134A. I can buy it here for about 12$ a can. it is susposed to be an "organic" refridgerant. global warming of 0 and ozone depleting of 0. It works good for sure. It is propane based but is 70F less flamable than 134A, also if it did burn there are no toxic gasses produced, unlike 134A.
All this info is stuff I've read from the data sheets. I'm not promoting it, but it might work in your bus.
Nick

I had thought something similar too. I've entertained thoughts of different refrigerants, and actually installing an regular electric compressor with inverter and plumbing it in.

Now, if the HC12 is more efficient with it's latent heat, and pressures, that may be something that I would consider.

Head pressure is not a problem at all. Last year it was, with an oversized condensor, I had overcharged it, and it was running about 255# head. This year, I added a receiver and silinoid valve to the front evaporator that I could turn on and off to experiment with. The interesting thing that I noticed was: the front evap doesn't get as cold. I'm only running about 100-150# head pressure, and that's with a sufficent charge (added a site glass). That fixed orifice isn't allowing enough refrigerant through with that lower head pressure. But's it's a catch 22, more refrigerant in the front evap, means higher suction pressure, and less of a delta T in both evaps. Higher head pressure reduces the capacity of the compressor. I'm getting it's rated capacity, but that means it takes a full hour of run time to get down to temperature. Hardly any of our trips take that long.

what the chances of using an RV roof mounted style fully self contained A/C unit?

Have you gone through all the normal trouble shooting steps? Although your application is rather unique (and BIG;) ) maybe it can be serviced by the existing components. Perhaps it just needs a tune up (leak, low refridgerant, restricted orofice tube, dirty condenser, dirty coil....). I'm in the dark on most of the ac particulars, but if it were my money being invested, I'd try to make sure that the ac system was in perfect working order before getting into major changes and upgrades.....my 3 cents.

It is propane based but is 70F less flamable than 134A...
Nick

R-134A is not flammable at all. If this HC12 is propane based I would not want to be the one trying to braze up a leak on cracked line. I work in a research and development lab for A/C and refridgeration systems and I have never heard of HC12. Taking a quick look at the MSDS sheet makes me suspect that the EPA does not like it because of the flammability issue. This stuff needs only a 2% concetration in air to be flammable.:eek:

This stuff needs only a 2% concetration in air to be flammable.:eek:

Just for reference, what's the LEL of R-12? Propane?

Troubleshooting steps are well past done. Compressor is pumping like crazy, weighed in charge, as per Carrier Transicold a/c's nameplate rating, skirt mounted condensor clean, clear, both fans spinning . . . all the bases covered. Even Carrier said, add another compressor.

The rooftop idea has crossed my mind. Might opt for the second alternator, and inverter setup, so it can run down the road. Anyone know *for sure* what inverter rating you would need to overcome locked rotor current on the compressor?

I used to be a volunteer at the New Canaan Fire Department. When they ordered one of the rescue trucks, they saved some money by going with a dual alternator with power inverter in lieu of an on board generator. When it works, it's great. However, it has a tendency to go through alternators. The demand on the alternators was probably higher than what the ac system will draw. However, it's something to consider. Fitting a belt driven compressor is probably the most cost effective approach (long term). Back to the MSDS on HC12....it's true, it's flammable. It's upper and lower explosive levels are nearly identical to that of propane. Many guys are running propane on their trucks safely, although not in the ac system. I don't know what happens when you run it through the ac system, but what's the worst thing that could happen;) ?

Maybe it's a stupid idea, but you could install a 'second roof' on top of the roof, like a luggage carrier. It would just be a plate across the roof, a few inches above it to let the air flow in between. The bus would always park and drive within it's own shadow, and maybe that will just help the AC enough to keep it cold.

Maybe it's a stupid idea, but you could install a 'second roof' on top of the roof, like a luggage carrier. It would just be a plate across the roof, a few inches above it to let the air flow in between. The bus would always park and drive within it's own shadow, and maybe that will just help the AC enough to keep it cold.

Now that sounds like a simple yet effective idea. I wonder if it would work?

Maybe it's a stupid idea, but you could install a 'second roof' on top of the roof, like a luggage carrier. It would just be a plate across the roof, a few inches above it to let the air flow in between. The bus would always park and drive within it's own shadow, and maybe that will just help the AC enough to keep it cold.

maybe not so stupid. This may be a thought in the right direction. What is the roof insulation like? Probably no more than a headliner, right? Maybe if you get some of that aluminum reflective insulation from Lowes (the stuff with the clear plastic foamlike core) and add it between the headliner and the roof, it will reduce the heat load. Window tinting helps, but makes backing up at night more difficult (solved with additional back up lights).

If you can keep the bus 10 deg cooler before you turn on the ac......probably a big PITA but worth considering

Do you have a window up near the roof you can crack open and let the hot air out the top? I crack my back windows a hair when I first get in and the cooling seems to fill the cab quicker.

It has a roof hatch which I pop when I park. There is a double layer of fiberglass with some (little) fiberglass insulation in between the two "layers." It's kinda like an exterior and interior shells put together.

Windows are tinted with the stick on tinting flim for now to see if it makes any difference or not. (Some, not much)

Keep them idea'rs comin'.

Here is what I found on HC 12, I would think a fellow that works in the AC field surely would have heard of this stuff before.
Question: I'm certain I read or was taught on a HRAI (Heating,Refrigerating and Air Conditioning Institiute of Canada) course that if 134A was set on fire it gave off a toxic gas (or was that R12??) as I understand it, the risks of something exploding is so remote its near impossible (or so I've read)

http://hc12ausa.com/hc12/legal.html


http://www.hc12ausa.com/hc12/msds.html


http://duracoolky.com/

http://hc12ausa.com/hc12/faqs.html

Here's the warning on 134a: Contains 1,1,1,2 Tetrafluoroethane (CAS 8111-97-2). Avoid breathing vapor. Use with adaquite ventilation. Inhalation of high concentrations of vapors may cause death without warning.

Considering the last part of the molecule is ethane I'd figure it'd combust under the right circumstance.

:weld:R12, and I think 134a will give off Phozgene (sp?) gas when burned. Unmistakable when you do it. I've torched a few lines while still outgassing,

bad bad idea.:badidea:

Here's the warning on 134a: Contains 1,1,1,2 Tetrafluoroethane (CAS 8111-97-2). Avoid breathing vapor. Use with adaquite ventilation. Inhalation of high concentrations of vapors may cause death without warning.

Considering the last part of the molecule is ethane I'd figure it'd combust under the right circumstance.

That warning goes with all refrigerants that I can think of. It is not because R-134A is toxic to breathe, it is because R-134A like any other heavier than air gas will tend to pool in low lying areas and displace the oxygen needed for breathing.

I happen to have the MSDS for R-134A right here on my desk. Under the "Fire fighting Measures" section it lists:

Flash Point :No flash point
Flammable Limits in Air, % by Volume
LEL :None per ASTM E681
UEL :None per ASTM E681
Autoignition : >1369 F

It goes on to say that a mixture of R-134A with high concentrations of air at elevated pressures and temperatures, and especially with oxygen levels greater that that in air, may become combustible under the right conditions. Of course if you mix enough oxygen in you can get pretty much anything to burn.

Here is what I found on HC 12, I would think a fellow that works in the AC field surely would have heard of this stuff before.
Question: I'm certain I read or was taught on a HRAI (Heating,Refrigerating and Air Conditioning Institiute of Canada) course that if 134A was set on fire it gave off a toxic gas (or was that R12??) as I understand it, the risks of something exploding is so remote its near impossible (or so I've read)

http://hc12ausa.com/hc12/legal.html


http://www.hc12ausa.com/hc12/msds.html


http://duracoolky.com/

http://hc12ausa.com/hc12/faqs.html

I glanced through that site briefly. They seem to infer that R-134A is an ozone depleting refrigerant, it is not, although it does have a low global warming factor. That is why anyone can buy R-134A without a refrigerant handling licence like is required for R-12 or R-22. R-134A does not contain any chlorine which is the element that breaks up ozone molecules. As to why we don't test systems with HC-12, That I'm sure goes back to the flammability problem. When choosing which refrigerants we will design and qualify new equipment with, a number of properties may get a potential refrigerant crossed off the list real early. High flammability, like HC-12 has, would be one, as well as if the gas is toxic or a carcinogen, or if it not compatible with available refrigeration duty oils. Cost, thermal efficiency, and even gas density are also very important, of course. R-134A is not quite as efficient thermally as R-12 was but it is fairly close. If the system was properly designed to run on R-134A then it will work fine.

this may or may not be of help, but when I was a kid, my parents had an '85 chevy van- 11 passenger ( 8 kids in the family). The AC in it was always ice cold. It only had ac up front. Here's my theory: the van we had was a gasser, regular rpm when driving about 2000-2500...yes? Diesels have lower rpms while driving. The compressor's not turning as fast as in a gasser. That's probably a contributing factor, as I'm sure gm uses the same compressors in both gassers and diesels.

What if you put a smaller pulley on the compressor? With the right size pulley, you could increase compressor rpm by 10-15%.

Interesting you bring that up. I was thinking that yesterday while sweating/driving. I put it in 3rd and drove for a few miles, and noticed a reduced suction pressure and improved TD out the vent too.

So, where can I get a smaller pulley for this thing at?

Next question I'm looking up here is the compatability with the hoses with old refrigerant. R12 that is. No, I'm not CanidianRigger here with boo-koo bucks, but I do have a little stash of the stuff in the basement, and I am researching the possibilities of dropping that in and seein' what could happen. I don't want to booger up the whole system and be with out here either.

Last thing I'd like to do is improve the subcooling off of the condensor. I installed a liquid receiver off of the condensor to improve the heat transfer capacity of the coil and keep it in latent heat transfer mode. This resulted in a an improved heat pressure, but the liquid line is so hot, you just can't touch it. I shot it with a water hose yesterday, and gained about 6°F TD just at 1600 rpm.

I really don't know that a smaller pulley is available...if there is, I think my theory is sound. This one will most likely require a trip to the junkyard. Look at any small gm car with ac.....