Anatomy of AC, dual units, and conversion help

[Manchild-SKO]

Greetings,

Trying to get a more solid grasp on the HVAC system on my bus, help would be greatly appreciated. I've read dozens and dozens of threads, scattered about the internet. This thread is an attempt to get some clarity for the average user with pictures.

Bus: 1999 Ford E350 Cutaway, 7.3l diesel motor, SRW (single rear wheel, as opposed to a dually), converted by Girardin, 4 window.

Knowns:
-there is a dash AC unit, I dont know if it works independent of the rear AC.
-there is a rear, ceiling mounted AC unit (Carrier, R134A, evaporator and blower).
-there is a side-skirt with 2 fans over a condenser, with what I believe is a dryer.
-there are two lines from the engine compartment to an auxiliary heater in the back of the bus, those two lines have a ball valve to isolate the rear heater.
-there are three radiators, one large (engine), one medium (?), one small (?)

Unknowns:
-does the van have a stock compressor? guessing yes
-are there one compressor or two? guessing one
-can I run the dash AC independent of the rear? guessing no, as there is a t-fitting after the condenser coil that runs a line to the front and the rear of the bus.

I have removed the rear AC evap and blower unit (lines are still in place), how would I go about getting the dash AC to work? I see the t-fitting that is after the condenser on the chilled line, however the hot line appears to only run up to the engine compartment. Would it be as simple as changing the t-fitting to an elbow fitting to isolate the front from the rear, and then capping the hot line that is running to the rear from the front?

I understand the benefits of an on-road AC unit. However, the cost on space is too high for my application that I use the bus for 75% of the time. I have another thread started about having a quick-disconnect AC system for the rear, or recommendations for a lower-profile evap/blower.

I've numbered each of the pictures so that we can all stay on the same page when discussing different parts.

 

[Manchild-SKO]

Here are the rest of the pics

 

[cadillackid]

this is correct.. there will be a sercond T underneath at the condenser like shown. there is only one hot gas line since the condenser is shared.. on this type of system there is no second condenser up by the engine radiator.. on a bus you will almost always have a transmission cooler and sometimes if your brakes are hydroboost there is a powered steering cooler.. engine oil usually doesnt have an external cooler on a 7.3 (ive rarely seen one but it is possible).. so thats why you only have one gas line going from the compressor to the condenser.



if you do not need the under-bus space you can remove the 'T fittings for the rear and pipe directly to and from the dashboard evaporator only and have the dash air using the under-skirt condenser.. if you need that space then you'll have a lot more piping and work to do installing a van condenser in front of the radiator..

 

[Manchild-SKO]

Thank you good sir. If I understand correctly, there will be two T-fittings then? One next to the condenser on the side skirt and another in the engine compartment?

If there are two, and I replace the T’s with Elbows in the right configuration then I can run the dash unit using the skirt condenser correct?

 

[hidefr]

Thank you good sir. If I understand correctly, there will be two T-fittings then? One next to the condenser on the side skirt and another in the engine compartment?

If there are two, and I replace the T’s with Elbows in the right configuration then I can run the dash unit using the skirt condenser correct?

Hi Manchild, could you let us know how this worked out?
Were you able to remove only the rear evaporator and keep the dash A/C?
I have a similar configuration on my 2009 Chevy Express 3500, 2010 Bluebird, with Carrier A/C and I would also like to remove the overhead evaporator but keep the A/C. I'm struggling to find good instructions, but your labeled pictures have been helpful.

 

[Manchild-SKO]

Hi Manchild, could you let us know how this worked out?
Were you able to remove only the rear evaporator and keep the dash A/C?
I have a similar configuration on my 2009 Chevy Express 3500, 2010 Bluebird, with Carrier A/C and I would also like to remove the overhead evaporator but keep the A/C. I'm struggling to find good instructions, but your labeled pictures have been helpful.

At the end of the day, I decided to keep the overhead evap, for the following:

-the dash AC simply cant keep up with the heat of anywhere in the US in the summer. Even when it was only 75 outside, driving down the freeway with the dash AC on blast it just wasnt enough. ANYTIME it was over 75, I would bake.

-T-ing off the AC lines turns into a major pain. You wont get rid of the extra length either, unless you have new high pressure lines custom fit which was going to be around $900 for both lines, also the fittings are not standard and will need to be sourced which was a huge pain.

-I learned to deal with just the dash ac by hanging a sheet from the ceiling to the floor immediately behind the drivers seat. This works okay if you're solo, but the rest of your crew, if any, in the back will melt faster than a pocket full of M&M's. The other problem with this setup is that if you are driving a far distance, and then plan to sleep in the back, the back of the bus could be as hot as 138 degrees F (that F is for F***, not Fahrenheit btw). This isnt an exaggeration, I measured with an infrared thermometer several times. Exterior temp was never higher than 92. When you super heat your living space like that, its not like you can just open the windows and vent it out. EVERYTHING in your house space is now 130 degrees and will continue to emit heat until it is ambient temperature. In my experience, even with temps in the low 60's at night, with a fan going for circulation, you'll never get your interior temp below 85 before the sun is back up.

So, fast forward almost 2 year, and 160 odd nights in the bus (I do tradeshows around the country all summer/fall and this is where I live on the road), here are some best practices.

1-Keep the rear AC. I took mine off the ceiling and mounted it vertically on the wall in the back, below the window, with the vents on top. I also removed the plastic covering of the evap unit (cosmetic) to make it a much more manageable size. You may need to disconnect the two lines on the evap to move it to the wall. If you are disconnecting the lines, keep in mind that they are high pressure and wreck you if you get 200psi of freon to your face. Refrigerant is also heavier than hair, so if you are doing this inside the bus, all windows and doors open and a fan on. Dumping refrigerant into the atmosphere is not good though, its bad for the environment, for your health, and is more costly at the end of the project. Get an HVAC tech to come over and capture the refrigerant. Then when you're finished mounting and hooking it all back up, they can refill your system. It was $280 to refill my system from empty, vs maybe $30 to top if off and another $50-75 for a house call from an HVAC tech. You dont need to shorten your high pressure lines if you keep the evap unit. You will have some extra length though. I coiled mine up and zip tied it out of the way up underneath the bus to the chassis. 48,000 miles later and I've had no issues.

2- Cooling strategy. Keep in mind that most of these systems require both the dash AC and the rear AC to be running at the same time to be working. Hence, you cant run just the dash or just the rear, they both need to be going at some level to work. The previous owner on mine said the AC system didnt work it all, it worked fine, he just didnt understand this concept. While driving, I usually run the dash cooling mid-max, with the rear on low. This keeps the entire cabin very comfortable. When I'm an hour or two out from finishing my drive for the day, I turn the rear up to max. Remember, its not just the air you're cooling, it is everything else in the back that is holding and storing heat. Thermodynamics are simple, everything that is hot will eventually get cold. Depending on how the ambient temp is, the emissivity of the material, and a few other things, will determine at which rate everything is cooling down. So you need to provide an environment in which all your stuff (bedding, pillows, jug of water, wall covers, the aluminum panels, your seats, backpack, clothing, all of it) can have a place to send their heat. This is why, when you turn your AC off because you're cold, 20 minutes later you are hot again, even if the outside temp is only 50 degrees. Its because of all the stored heat. So, cool down as much as possible, as early as possible before you are going to stop for the day.

3- AC and fuel economy. I grew up in a house where AC was synonmous with worse gas mileage. This may have been true 30 years ago, and is still has a small effect today, but by and large, you wont see an appreciable difference in MPG using or abstaining from AC in your bus. My observation over the last 18 months of hot summers and cold winters, in my 99 E350 7.3 diesel shortbus, is that running AC on max doesnt affect my mpg more than .1 or .2 mpg. You might see .1 or .2 and think 10 or 20%, but that would be assuming you are getting 1mpg. I'm towing a 16' enclosed trailer, weighing 7,500-8,500lbs, and I get 7.8mpg at freeway speeds (70-75mph) and 8.8-9.2mpg at 55mph. No trailer at 55mph I can get 12.9-13.1 mpg, 9.8mpg at 75mph. Its an SRW running 265/75-16 wheels with BFG KO2 AT tires at 60 or so psi.

In summary, keep your rear evap. Mount it to the wall and it'll be out of the way. I also had planned on building either a cabinet around it or a steel cage with tie off points for strapping stuff to it. At the end of the day though I dont even notice it is there. It sits 6" below my bed frame that I have mounted to the wall. It is the simplest way, most comfortable way, and easiest way to deal with that blasted overhead evap

 

[cadillackid]

great write up!! from your experience.. and one reason i wrote the thread on think before removing the factory AC...i personally add AC to every bus i get if it doesnt have it