R407c Conversion for 1989 MCI A/C

[jap42]

My bus has had the R22 replaced with R438A (MO99) which is a drop in replacement. Unfortunatly it has mostly leaked out because of the compressor sitting for 3-4 years. This stuff is expensive. over $250 on ebay for 25 lbs.

I am thinking of doing a full swap to R407c but I have to replace a portion (At least 20%) of the oil to synthetic POE oil. Just wondering if anyone else has done this. The POE replaces the mineral oils in electric compressors fine. So I dont see a reason why the compressor in my bus would care. Plus I think I can swap well over 50% of the oil considering I can drain the compressor.

Also, is the oil pan under pressure from the refrigerant? The service manual talks about replacing the oil like its no big deal.

[freds]

I have no real expertise in this area, however would very much like to hear your final result as my bus is still (I think charged with R22 for the drivers area air conditioning if I ever figure out what it takes to turn it on.).

My understanding is that you have to be certified to work with R22 but as a back yard mechanic you can do all the other types of refrigerants.

[lvmci]

Nick Badame should be able to help...

[jap42]

I have no real expertise in this area, however would very much like to hear your final result as my bus is still (I think charged with R22 for the drivers area air conditioning if I ever figure out what it takes to turn it on.).

My understanding is that you have to be certified to work with R22 but as a back yard mechanic you can do all the other types of refrigerants.

You have to have your EPA certification to work on any refrigerant. There are a few types. You can get a type 1 online in about a hour and get your card so you can buy refrigerant. Technically you can only work on small appliances but for personal projects I don't really care. The systems in these MCI buses are massive, More like commercial refrigeration then an automotive system.

For you freds, I would call around to some local hvac contractors. R22 is getting very expensive and some guys might be willing to evac your system and recover the refrigerant for free if they can keep the R22 to reuse somewhere else. Then get yourself a Gauge Set, a can of R407c, and some polyester oil and refill it. Like my original post though, I am not 100% sure about the new oil in the old compressor. I am pretty confident it will work fine, but I was hoping to hear someones first hand experience.

[chessie4905]

Mostly leaked out... Better find and repair leaks first, including compressor seals. Charge system with nitrogen and do a full system leak check.
This is also why it is not advised to maintain the old coach air conditioning systems unless you dont mind spending a lot of time and money doing it. Use that money for roof airs and a genny, minisplits or some other setup and remove most of the factory system and its complexity with 30 plus years of wear and corrosion.

[Jim Blackwood]

Very polarized topic. Older buses, roof air seems to be the way to go. Newer ones, you might want to keep the OTR system but change it a bit to suit. Plenty of discussions about that. Might have to go to the commercial AC forum for your oil question though.

Jim

[luvrbus]

Get you a bottle of nitrogen and find the leaks it gets old pulling a vacuum and 30lbs of Freon every year,it cost you a fortune to bring a old neglected system back to life and make it last     

[jap42]

The bus has low mileage and pressure tests fine. The front crank seal on the compressor is a double stacked oil pressure seal. When they sit the oil drains out of the seals and Freon can escape. I have found out a little more on the compressor, It looks like the seals can be swapped for double lipped spring seals. The condenser is a little rough but not leaking. I was thinking about making a timer setup to automatically fire the engine, and basically actuate everything to keep things freed up. Kind of like a standby generator. Firing the motor up once a month to keep the seals lubed is not a bad way to go and not spend all that time on upgrading.

A month or so ago we were talking about adding an electric pump along side the OTR. I am thinking of swapping the electric pump in and replacing the OTR pump with a large generator to run that and charge a battery bank. I do have mini splits I am installing but only 12000 btu to stay at 120V. 12K should be enough for the bedroom. I may end up upgrading the front for a 24K with a dedicated inverter.

There is deffinatly some difference of opinion, lol. When I suggested replacing the system everyone said leave it alone and use the factory system because nothing will match it. I am thinking factory system but with an electric compressor. Maybe 24V compressor. Anyone know what the alternator capacity is? Considering all the lighting that used to be in the overheads that is gone I might be able to replace that load with the compressor.

[chessie4905]

There was an episode on How its made last week. It qas about a refrigeration system for a truck box or something. They had  one compressor run by a 12 volt motor and  a 110 or 220 volt motor to power compressor when plugged into shore power. Both motors had belts hooked to compressor. If one motor supplied the power to turn compressor pulley, the other motor just spun with its belt and pulley. Pretty cool idea. The system was designed for cooling or freezing.

[Jim Blackwood]

Very unlikely your lighting loads will come anywhere near your compressor demands and battery requirements to run a compressor will be high. You could end up with a marginal system in many ways if you aren't very careful. Power density in batteries is still well below petrol pound for pound.

Conventional wisdom says use the diesel for high capacity cooling, shore line if possible and then generator power, and batteries as a last resort. Propane is in there with the generator somewhere. Departing from that sequence is likely to be expensive. On a currently leak free system you have every option though.

There's no getting around the fact that nothing is going to cool down the bus as well as the OTR AC. If you plan to belt the OTR compressor to a DC motor your first step is to get the RPM and HP requirements of the compressor. The rpm you can figure from the belt ratios, and the HP should be available online. Then price out a DC motor that can provide those numbers. It ain't gonna be cheap. My guess is several hundred to over a thousand dollars. Then look at the current drain. That could run a couple hundred amps continuous or more. Which probably means a couple thou more in batteries for even marginal performance. That's also going to require heavy power cables, and the beat goes on. But check it out, you may be the person to find a way. Still and all there are reasons why commercial AC units often run on 480VAC.

Nothing wrong with firing up the 60 series to draw down the temp and then use a smaller AC to keep it comfortable. Good for the engine to run a bit every now and then as well.

I still think an enclosed compressor of about 3 ton capacity, just enough to run the rack AC units could be the way to go. Shut off the main evap and dash unit, bypass the main compressor, run it on shore power or the genny. Possibly battery and an inverter. I doubt any less would be enough for a DL sized bus, but once the OTR charged the system and got rid of the heat load it should keep up fairly well. It could possibly be mounted in the condenser bay.

Jim

[chessie4905]

I didn't infer to run the coach compressor with an electric motor. Maybe the one GM used and also in cars, but still not attempting to run off batteries and or inverters. That was more for the fanatics that want to cool their coach with something small and efficient. Me, I'll use roof airs and generator when necessary. Maybe not nearly efficient, but has good history of relialibility. Just like electric water heaters, and propane furnaces.

[luvrbus]

I have a friend that owns over 100 motor coaches (buses) he tells me that keeping the HVAC systems going is the exspensive part of his normal maintaince program and getting worse with the newer bus with all the electronics.I have 60,000 btu's of road air it works fine here in the heat,with the dash unit and a rear unit it has a good size belt driven compressor but not near as big as the O5G Carrier

[jap42]

I hate the noise of the roof units, I think my plan for the mini splits will work really well. I am going to try 2 12K units to start. I can up them to 24K but I want to see if I can stay in that 120V range.

So far so good on the 407c swap. I recovered the MO99, even found someone at the supply house that gave me $50 and a empty recovery tank for it. I drained the oil (Rapidly). It was like open a shaken soda. Then I cleaned closed it up.

The compressor has a fill port toward the motor that has a shrader valve. I did not have a oil pump or a funnel to fill it. So I used my high pressure hose from my gauges and connected it to the fill port and dropped the other end in the oil after cleaning the hose extremely well. Then using the low side port I pulled a vacuum. It sucked the oil up perfectly.

I sucked in one gallon (8 pints). The service manual says 9 Pints but if the compressor is level then I am perfect in the sight glass. On the normal angle I am at the top of the motor side and bottom of the curb side.

Again, sealed it off, cleaned my high pressure hose again and vacuumed down. Thats where it is now. We will see how the vacuum looks in the morning. Run the pump a little more to be sure and the tomorrow night I will fill with the 407c.

The 407c should give me a 5-10% improvement over the MO99. Some people have said its 5% less then R22 some said 5% more. I'm not sure which. I am hoping for ice cold. It is suppose to rain this weekend so I am hoping to get the running so I can work inside the bus over the weekend.

I am thinking it would be worth running 410a as I think the compressor can pump it fine, if I wanted to take the time to swap out the expansion valves.

25# can of 407c = $160
1 Gallon RL68H Poly Ester Oil = $135    I actually found this on the MCI website. The newer busses with 134a use the same compressor and run this oil. So that was really my only concern was oil compatibility. From everything I have seen on the 407c, you only need to replace 20% of the mineral oil with the synthetic. But it is so easy to do I figured replace as much as possible. I would say there may be a pint of the old stuff left.

[jap42]

So all my leak tests went well and the bus cools like a fridge. I had the late afternoon sun beating in the front windows and down the side and the whole bus was cool in about 20 mins.

The oil level looked great, the polyester oil might have actually dissolved and brought some old mineral oil back to the compressor. The level dropped and then came up a little higher then it started. Its pumping and splashing and not frothing.

I would defiantly recommend the swap. You should leave this to a licensed HVAC pro if you do not know what you are doing. But if you have a good mechanical ability, its not hard to learn enough to do a lot of your own service safely on this system. Like I said before, EPA certs are pretty easy to get and then you can buy the R407c and sometime you may need it to buy tools.

The process is like this:

• Make sure you know what you are doing before starting. Refrigerant in this system is under very high pressure. Escaping gas can cause injury and possibly death. When refrigerant is in motion it can cool your tools, lines, and parts of the system enough to cause frostbite. Releasing any refrigerant into the air is illegal. Al Gore will come find you and give you a 2 hour lecture.
• recover all existing refrigerant and pump down the system
• Drain the compressor oil (Use caution, refrigerant can be disolved in the oil and cause excessive foaming and pressure)
• Replace drain plug and pull vacuum
• Place hose in compressor oil and attach other end to fill port on compressor
• Once the compressor is full of oil pull vacuum and charge with R407c using normal procedure

[RichardEntrekin]

Nice.

When I got into the RV ownership world, I saw quickly that the AC systems were areas that needed care, and it was very hard to get an AC tech to work on them. So I did as you, I took the EPA test, got my card to buy refrigerants, and I read and read and read until I understood what I was doing. It helped that the Chem Eng degree my mother paid for was put to use.

All of that to say, I really appreciated the approach, the documentation on the forum, and the final result. I am impressed with what you did, and it will help another bus owner in the future dealing with replacement of R22 in an existing system. It was very clear that you did your homework, and the payoff was there.

Kudos to you.