M2 Freightliner Ambulance Conversion Project. 2007 Crew Cab


Expedition Leader
These are usually rescue rigs. So they carry a lot more equipment than just the paramedic side. Fully kitted out they run between 16000 and 20000 lbs. This one for example has storage for 6 SCBA tanks in the module and 3 in the cab. Plus the extraction gear.

Ross's was a neonatal transport rig and was initially setup to have a lift for the incubators.

But we are seeing a lot more of the heavy van based units over here especially in the centers of the bigger cities.


Expedition Leader

I just found this thread and thanks for posting the link in the old thread.

It was good finally meeting you and your wife, and spending a little time turning wrenches, even if it was in a parking lot. The pictures I took didn't turn out very well and they're all very dark. I guess something was set wrong on my new camera and I missed it.

Your pictures however, cleared up several things I was trying to explain to Bob, like the gap between the cab and module, and the overall length. I was guessing at the measurements and everything looks different in the dark anyway.

Once you get that O2 Sensor Alarm figured out, please let me know how the little device that Bob designed and I built works...or doesn't work. :)

Anyway, I'm glad you guys made it back home safe and sound, and I'll be following to see the progress you make on this build.

Oh and for you readers, this is really why he bought this truck...


...it came with his very own Firefighter's helmet!
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Some measurements (so I don't lose them)

View attachment 376975
I have the same module dimensions - a 14 ft box with a 17" rear bumper, which gives me an overall vehicle length of 24'-8". It fits my garage (28'-6" inside), but the rear bumper will become a piece of 4x4 or 6x6 box tube to give me a few more inches of clearance - since I don't plan on backing into hospital loading areas, the rear dock bumpers will maybe also go away. My overall height is 9'-6" with the air ride up, so I can clear my 9'-11" garage door opening.


Expedition Leader
No troubles finding the cables for the cruise switches on this one. They even have labels on them.

And I managed to get rid of the air leak (well as far as my deaf ears can tell). Switch on the drivers air ride. I sometimes wonder if air ride is worth the hassles. We went away from them around 1990 and went with spring/rubber and damper type suspension seats due to the high number of failures taking machines out of service)


Expedition Leader
Just digging back through the maintenance history and noticed another little gem. This unit had been prepared to be a spare in July-August 2016. Including full service (fluids, filters, air dryer) but also amazingly it also included replacing the rooftop AC, all 4 batteries plus front and rear tires. From the looks of the nipples on the tires it never went back into service afterwards.

Bonus. :wings:

M2 service history.jpg
You really lucked out! The using department was large enough that they just didn't run the unit if and when needed, they maintained it to ready for full service condition! Every Medic Master medium ambulance I've run into uses 4 Group 31 batteries, and at about $100 per each, that alone is worth a smile - not to mention new tires!

If they had done all that to the unit, I wonder why none of the AC worked?

If you got all the maintenance records, did you also get the Medic Master manual?
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Expedition Leader
I think the AC is tied in through the V-Mux system and was getting load managed due to the low voltage alarm. Haven't had a chance to chase it down yet (and it actually too cool in Phoenix to test it). I think I will dig into the harness and bypass all the load manager and temp controls via the V Mux and bring it back to the dash controls. One of the problems is the thermostat is via the VMux and it is controlled from the display in the back.

Eventually I will probably remove the 2nd engine mounted AC system and replace it with a 110v mini split system.
That's a common item for the load management system - the AC is normally on a 60 amp circuit, and pulls about 45 amps when it's running (condenser and evaporator blower). Other things in the load management circuit often include an IV bag heater, and sometimes exterior flood lights.

One thing to remember is that the module (the ambulance portion) controls the entire heating/cooling system on a Medic Master, including the cab. If the module doesn't want heating or cooling, you will get very little from the Freightliner dash panels. About all the Freightliner panels will do is vary the cab blower speed, or adjust the cab temperature a little. The key is to set the module temperature fairly warm in cold weather (maybe 75F), and fairly cool in warm weather (maybe 65F). The cab can then do its own heating/cooling thing. I found this out when we brought mine back from PHL in May of 2014. We didn't have a lot of air conditioning, and no heating, because I didn't know that I needed to turn on the magic panel switch "Heat/Cool". When I found out how to use the system, I had it all -- heat, plus AC. If you have a walk through or a large window between the module & cab, leaving it open helps control the cab temperature a little.

Before you start chopping wires, maybe see why the battery voltage is low - it could be bad batteries, a poor connection, or a regulator problem. MNtal had alternator problems on his freightliner/Horton ambulance, but instead of spending many bucks on a new 270 amp alternator, he was able to get his rebuilt very reasonably. I'm guessing that you might have one bad diode in the rectifier portion - we ran into that a lot with M60 series tanks, and the maximum voltage we could get would be just over the 24 volt battery voltage instead of the 28 volts we wanted.

The second engine-mounted AC system is just for the module - if it goes away, the module can get hot while you're traveling, then the split system has to start with a high temperature. In my opinion, I'd keep it.


Expedition Leader
Battery voltage problem is sorted. Somehow it had multiple loose earth connections (batteries and VMUX modules). Tightened them and it was fine. The auxiliary engine driven AC is a twin unit with a single compressor (original cab system is separate from aux). It has condensers and evaporator for the module and in the back of the cab. If I remove it I will replace it with an inverter/generator powered mini split system. The mini split would also replace the rooftop unit. Obviously I would need a remote start generator or a separate alternator feeding the inverter for the mini split.

But that is a project way down the list. I will checkout using the rear controls to see if it helps with the front can AC compressor (after doing a system pressure check for LP)


Expedition Leader
This is what they have now instead of a manifold and a couple of pressure switches. All connects into the canbus. Replacement $120.



Expedition Leader
Ok I think these guys are trying to turn me into a conspiracy theorist. I went to change out the AMU today and found there was one airline from the AMU going nowhere. It looked like it went straight to the 2nd air tank which had a shiny new brass plug screwed into it. So I went to NAPA and bought a gold plated platinum fitting and hooked the pipe to the tank. Tada no more low air pressure alarm. Was this just a conincidence or was someone tampering with this rig to try and buy it on the cheap.

If you look at this photo you can see the green pipe near the new brass bung.

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