LMTV Air Conditioner AC Main Unit Gen1 and Gen2 Details

Starting a new thread to have this info easily available. I will be updating this post with pictures and other information scattered throughout this forum. Some info and pics were gathered from others who are on the quest for a cooler cab. As I add pictures I will probably group these details in a more logical order so for now just listing what I know.



1. Gen1 and Gen2 AC units have different wiring and how they operate.

2. Gen1 and Gen2 units are also physically different sizes both height and depth however they both slide easily into the stock heater slot on the LMTV.

3. Gen1 units use similar cables to operate the vent, defrost, heat functions just like the stock heaters except they have rotary knobs instead of the pull knobs for the cables. So Gen1 uses just the stock heater 12v/24v power cable.

4. The best way to summarize the two is that Gen1 is mechanical like the stock heater and Gen2 is electronic.

5. Gen1 uses a mechanical fresh air vent door the same as the stock heater in front of the radiator behind the grill. Gen 2 has a door that is internal to the unit so the opening for the fresh air vent is covered by a mesh filter to prevent debris clogging up the door.

6. Gen2 units also use the stock heater power for fan and lights. The fan is 24v and the dash lights are 12v. The factory plug provides both 12 and 24v. MOD: I tapped the 12V dash light power wire on the Gen2 unit to provide dash light power to my aux switch box.

7. Gen2 requires an additional 24v power source to operate the various controls, vent, defrost, etc. They use electrical actuators and WILL NOT FUNCTION if you just have the stock power plugged in. You will only have fan and dash light control. The power plugs are standard SURE SEAL 2 contact connectors and are the same male end plugs that match the female end plugs to the aux 24v power wires under the power distro panel. You will need to either cut the ends off the connectors for the additional power or find those SURE SEAL ones to make an extension wire that goes from the power panel to the 2nd power plug on the Gen2. I am in the process of wiring this item up.

8. The additional power wire needed for Gen2 also sends power to the condenser fans and compressor.

9. Gen1 and Gen2 have the same wire harnesses for all the other components. They are condenser fans, compressor, high pressure switch, and radiator fan cut out signal. This last one is so that when you are fording and flip off the cooling fan using the main dash switch it disables the condenser fans as well.

10. The stock condenser that has the wire harness on it connects to ALL the appropriate connectors on both the Gen1 and Gen2 units (electrical).

11. I claim full credit for labeling the different AC units Gen1 and Gen2

12. There are some one-off variants of Gen1 and Gen2 out there specifically Gen2 units that to me look like prototypes or early production models that are difficult to install due to side assembly bolts that interfere with sliding the units down into the stock heater location. The ones I have seen like this are tan in color. I don't know if we would call these Gen3 units or more likely Gen2 prototypes.

13. Both Gen1 and Gen2 units require weep holes to be drilled into the cab floor for the evaporator condensation drain. Gen 1 units typically have hard plastic drains that stick out below the unit and Gen2 uses 4 duck bill rubber drains with two along side the fresh air door and two more in similar positions as Gen1.

14. Gen1 and Gen2 evap condensation drain ports are in different locations so if you install a Gen1 and then switch to a Gen2 you will more than likely have to drill two additional holes into the floor of your cab.

15. The holes you need to drill into your cab for evap drains are DIRECTLY above the Charge Air Cooler with about 2 inches of clearance. When you drill these holes you have your cab down and must be VERY careful using your hole saw.

16. Gen2 units have a different physical space and cover for your Park/Trailer valve. They require you to switch over to the single Haldex integrated Park/Trailer valve (see my write-up on how to do this). Due to the additional electrical actuators there is less room behind the valve than in stock or Gen1 units so the two valve stock setup would be difficult to retrofit. The cover hole for the valve and mounting screws are designed for the combined Haldex valve and have a perfect fit.

Pic of wire harness for Gen2. Gen1 is the same minus the 2pin round connector for the additional 24v power (actuators and fans). Gen1 takes all its power from the heater power for the stock connector.

17. Pin outs for the 4 pin connector from the main AC unit Gen2 to the condenser (not sure if Gen1 wires are the same colors but I will verify tomorrow) Evaporator side colors:
Black goes to fan ground
Yellow goes to high pressure switch
Green goes to compressor clutch
Purple condenser fan power

18. Stock Condenser Wiring:
Here is a pic of the wire harness ends showing the two, two wire connectors for low pressure and high pressure switches and the single plug for the compressor.

(Wire identification and operation: Keith_J - "The white two pin plug w black wires is the low pressure cutout switch. The red two pin plug with purple wires is the high pressure fan switch. How this works? Low pressure prevents operation if refrigerant charge is low or absent. This prevents oil starvation in comp. Also, it prevents evaporator icing since temp corresponds to pressure.
High pressure switch makes fans turn on only when needed. Ram air at 58 MPH is more than needed so fans freewheeling)."



Live long and prosper (Spock)

OD

ahhhhhh... a Treky is among us.

Quick update... I wired up the additional 24v power source for the Gen2 AC. I didn't want to purchase a $300 crimp tool for the military grade power connectors so I just ordered waterproof 2 wire connectors from Amazon and soldered it on. Tapped power from the PDS. The aux power is used to power the vent controls on the Gen2 and sends power to the condenser fans. Actuators on Gen2 are pretty slick and very quiet as they move.... I will get pics of the wire harnesses for Gen1 and Gen2 shortly. I finally got my LMTV back together so I drove around for a bit on Sunday so didn't update this write up yet.

Stock condenser install will be next but may take a while since I HAVE to fix my no brake lights issue first. I keep putting that off because its not as much fun as mods.

OD

FYI when I wired the additional power source for the condenser during my install FMTV Air Conditioner Hybrid Completed Installation I used a 15 AMP fuse, based on the 15 AMP breaker on the side of the AC unit. One breaker is for the blower motor and the other is for the condenser fans and for other accessories, those are just the large power consumers. Any way when I started to test everything out prior to getting the AC 134a charged (with the compressor unplug so not to come on during testing) the condenser fan fuse blew and guessing something was wired incorrectly and something shorted it out, I spent many hours and went through all the wiring checking and re checking because I could not find the source of the short. So I put a new 15 amp fuse in and again it blew. Frustrated I decided to just put a 20 amp fuse in and see where the smoke comes from LOL!!! Surprise it ran for about five minutes then blew the 20 amp fuse. Next a 25 amp fuse and it all works great now. Whats surprising is that the power supply goes through that 15 amp breaker and it has never popped. So two things the fans pull more amps than expected and why hasn't the breaker popped!

That's interesting... hmmm. Good note on the power usage. That 5 minute run on 20 amp fuse then blowing... Did you touch the wiring and see if it was hot? I am not an electrical engineer but I wonder if the combo of the fuse at one end and the breaker at the unit would cause the first fuse blowout. With that aux power going to the unit at 24v is there any difference between a 15amp fuse for 12v vs. 24v? I know the relays have to be 12v or 24v specific.


One of those brakers goes to the 12/24v coming in from the stock truck heater plug with the 2nd for the additional power source.

Great info!

Also, I added a pic of the wiring connectors to my original post.

OD

No hot wires. As far as the fuse goes simply put amps are amps. The fuse doesn't blow because of what voltage it is it blows when it exceeds the amps rating on the fuse.
Also the 12 volt is strictly for the panel lights in the AC unit and is fused somewhere else before it gets to th AC unit. Not through the breaker.

ok, just wondering on fuses... Yep, on the panel lights only 12v use, I had that in #6 on my list. I tapped that line for my aux switch panel lights.

Well, I am thinking there is a difference in 12v vs 24v fuses.. would be a neat test to try a 15a 24v fuse in there. watts = volts x amps right? sure seems like a 15A fuse rated for 12v cannot handle 15A at 24v, with twice the volts... that means at 12v the 15a fuse can handle 180 watts vs 360 watts at 24v. Again, I could be wack.


Updated the formula


OD

It would explain you blowing the 15A 12v fuse then the 20A. At 25A and 12v it can handle 300 watts. Using volts times amps a 30A 12v fuse would be the equivalent of a 15A 24v fuse... 360 watts. And why the Gen2 15A 24v breaker didn't trip on the unit.

What are the wire colors? Doing the install on MKCs 1078 and the receiver pressure switch don't mate with any of the harness plugs. The pressure switch has three pins and is round. So probably wrong drier. This was part of the compressor kit so it could be wrong.

OK, the heat must be getting to me I think I understand now what you want...


Pin outs for the 4 pin connector from the main AC unit Gen2 (not sure if Gen1 wires are the same colors) Evaporator side colors:
Black goes to fan ground
Yellow goes to high pressure switch ( I think this is what you need)
Green goes to compressor clutch
Purple condenser fan power

Hope this helps. I will add this to my first post.

The giant 3 fan MRAP condensers I have that come with the dryer only have two wires going to them. Will take pics of that dryer tomorrow. I have three types of condensers I will be playing with: Stock LMTV condenser that mounts behind the front skid plate and bumper, giant 3 fan MRAP condensers with attached dryer that may go somewhere under the bed, and a 2 fan MRAP condenser that I have secret plans for. First plan is to mount up the stock condenser then play with options.

OD

Thanks OD for the prompt clarification. Yes, green to clutch is std in auto AC market. But the plug with the yellow wire doesn't mate to the switch on the dryer.

Then there is the other plug, also with two wires, which is unknown. Sorry, I'm a bit shelled from the heat as lunch was resampled around 1530 and have been feeling quite miserable.

Ok. Will look at my condenser harness in the morning. There should be the 4 pin to the condenser harness from the main unit, then a 2 pin to the dryer, and a second 2 pin that goes to the compressor. We may have a situation where there are two unknown pigtails that complete the connections to the dryer and compressor.

If this is true I will use a couple of waterproof 2 wire generic connectors to complete the connections.

Nice. Looks like there is a problem with the dryer switch type as it is a binary with three pins. This keeps compressor from running if charge is low or temperature to low.

Which means there are two switches in the system. As we have no hose kit yet, I didn't know.

The compressor has one service port but no high pressure service port.

Unfortunately all the pieces were sourced seperately so no telling if the condenser is a Gen1 or Gen2. The drier came with the compressor so no telling what it is either other than it has a 3 pin round connection. So the setup, other than the evaporator is not simply a "plug-and-play" combo.

Let me clarify my last post... When referring to Gen1 and Gen2 I am talking about the cab main unit with the controls. I have not seen the different versions of the condenser so I don't want to call them Gen1/Gen2. Although, why not start calling them Gen2 Condensers (with the L brackets) and give mkcoen ALL the cred Based on previous posts in other threads there does seem to be a versioning of the condenser based on what we have seen with different mounting brackets. The condensers I have for the LMTV all have the little L brackets to mount them.

The Dryer:
Here is a pic of the dryer that comes attached to the MRAP 3 fan condensers I have. I am not suggesting that this is the proper dryer for the LMTV AC setup but it does show a 2 wire connector for the high pressure switch.


Now here is the secret info (being humorous here): Here is a pic of the dryer that is claimed to be the LMTV dryer on eBay. It does not come with the high pressure switch but you can see the port for it. I may snag one of these and steal the high pressure switch from the MRAP dryer I have or just use the MRAP dryer. This is my 2nd option since the dryer on the MRAP setup is a LOT smaller than the suggested "real" LMTV dryer.

I did a little research on Red Dot dryers and I believe this may be the correct dryer for the LMTV.


Stock Condenser Wiring:
Here is a pic of the wire harness ends showing the two, two wire connectors for low pressure and high pressure switches and the single plug for the compressor.

(Wire identification & operation: Keith_J - "The white two pin plug w black wires is the low pressure cutout switch. The red two pin plug with purple wires is the high pressure fan switch. How this works? Low pressure prevents operation if refrigerant charge is low or absent. This prevents oil starvation in comp. Also, it prevents evaporator icing since temp corresponds to pressure.
High pressure switch makes fans turn on only when needed. Ram air at 58 MPH is more than needed so fans freewheeling)."




OD

Isn't the single green the compressor wire?

Yes MKC, the single plug green wire is the comp clutch. The whitebtwo pin plug w black wires is the low pressure cutout switch. The red two pin plug with purple wires is the high pressure fan switch of which I don't know location.

How this works? Low pressure prevents operation if refrigerant charge is low or absent. This prevents oil starvation in comp. Also, it prevents evaporator icing since temp corresponds to pressure.

High pressure switch makes fans turn on only when needed. Ram air at 58 MPH is more than needed so fans freewheeling.

It took 24+ hours to extinguish my helmet fire and make sense of the wiring.

The fan over ride is handled in the main evaporator unit. I doubt the binary pressure switch could be used so we have to source the correct pressure switches. I'm not familiar with the Delphi brand sealed connectors used. Hopefully someone at the auto ac shop knows.

ok great info I corrected my last post as well as the big list and cited credit to Keith_J with a quote from your post as well.

Do you have the hoses for your set? Any electrical connections on it? Could there be an intermediate wiring harness that would plug in between evaporator and condenser loom?

mkcoen,
You guys are out in front of me on the install. I have what I believe is the main return line from the evaporator to the compressor (big fat long hose). I have been playing around with how that hose routes down from the main unit to the compressor so let me know how you routed it. I have a couple of different hoses flagged and am watching on eBay but I wanted to see someone actually use them. Obviously we don't want to route those hoses anywhere near the cab tilt mechanism.

Here is what I am assuming, and please correct me on hoses. Big hose from the red, large port on the main cab unit to the compressor then smaller line, high pressure to the condenser, then dryer then into the smaller blue port on the main cab unit.

Where are you installing your dryer?

On the harnesses, it is my belief that the main unit harness plugs into the condenser harness we have been talking about then it "looks like" there are a couple of pigtails that go to the high and low pressure switches. They don't seem long enough at least for the compressor close switch. The wiring diagram for Gen2 shows it plugging directly into the condenser harness with the 4 pin plug.