Newbie, installing "custom" system

[Mogman]

Hello all from Papalote, TX
I am in the planning stage of installing an AC system on my HMMWV (military Humvee) the system I am installing has dual condensers and evaps. it would normally use a GM pancake compressor but because I am running an 08 LMM Duramax I will be using a 10S20F compressor.

I will need advice on such things as how to determine how much oil I will need etc.

On kink I am throwing in is I want to move the rear evap from where it would normally be which is on the floor between the rear seats to mounted up to the fiberglass helmet top roof to gain as much access as I can so I am not sure what issues that might cause as the system as is is relatively on the same plain as originally built, I do not anticipate this to be a big issue but some considerations may be needed.

[Mogman]

Looking at the specs the R4 has a 10CI displacement and the 10S20F has a 10.8CI displacement so that should be compatible, I plan on running a trinary switch and wonder what pressures would be right for this system.

[JohnHere]

I'm not clear about your project. Are you planning to take an OEM system from an H2 that uses a 10S20F compressor, front A/C only, and install it in your HMMWV, along with an additional condenser and added-on rear evaporator? Or, are you installing a new aftermarket front-and-rear A/C system with an additional condenser?

[Mogman]

I have a HMMWV with a Duramax engine, it has a 10S20F
I am installing a system from a later HMMWV that was always a 2 cond, 2 evep system but I plan on mounting the rear evap to the ceiling instead of the floor.
The condensers on that system are mounted in the rear fenders.
I actually have not settled on what rear evep I am going to use as I have several different units to choose from

[JohnHere]

I looked, but I don't have any specifications for your military Humvee with the Duramax turbodiesel V-8 and 10S20F compressor. If no one on this Forum knows, perhaps another board specific to your vehicle could provide the information you need.

Alternatively, I've learned that Classic Auto Air and a company called AVA (KT Performance) have developed reproductions of the original HMMWV 24-volt A/C system. Perhaps they might be able to help.

[Mogman]

They did not install Duramax engines in any military Humvee's so there are no "specs" for what I am doing

[JohnHere]

They did not install Duramax engines in any military Humvee's so there are no "specs" for what I am doing

I regret the misunderstanding.

Since we don't know how much refrigerant a system like yours takes, there is a way to "sneak up" on the approximate correct charge by starting at, say, 30 ounces, and then adding refrigerant from there. The idea is to monitor the pressures and central vent temperature while you're doing this until you reach the perceived optimum charge.

In a nutshell, the procedure is to add refrigerant to the nominal arbitrary charge of 30 ounces, about one ounce at a time, until the pressures and vent temperatures just begin rising, and then stop. It would be best to use an accurate refrigerant scale so that you can keep track of, and note, exactly how much refrigerant you install for later reference in case you need to service the system again.

Unfortunately, we have no choice but to guess at the total oil amount for your system. From what I can tell, most new 10S20F compressors come from the factory filled with about 5 fluid ounces of PAG-46. I would "guesstimate" that a total amount of 8 fluid ounces should suffice for your system since it is larger than a typical MVAC system (two condensers and two evaporators).

[Mogman]

Thanks, that is what I was looking for.
So using the ambient temp/high/low pressure readings chart is not a good way to judge coolant fill?
Also I am curious, when the oil is contained within the liquid coolant, post condenser it travels no problem up vertically with the liquid to the overhead evap?
Just a little concerned with creating a "trap" for the oil.
I will try my best to keep all the lines ether vertical or horizontal and not create any "traps" in any of the lines.

[tbirdtbird]

We seldom use any type of chart, they can be misleading.
The oil is dissolved into the refrigerant and travels with it.
How much of a riser will you have?
Bohica gives a super description of how the oil travels here:
https://autoacforum.com/viewtopic.php?t=14862

[Mogman]

Just a guess at this point but somewhere between 3-4 feet.