Coleman Mach 46515-611 Heat Pump
This section is about the replacement heat pump I bought and installed May-June 2023 to replace the tired and suffering Coleman Mach heat pump installed in 2002 by Winnebago. Go here to see the original 2019 maintenance article: 2: Heat Pump
Based on the appearance of the inside of the heat pump when I opened it back in 2019, the previous owners hadn’t used the heat pump very much before I bought the rig in 2016. Fairly clean inside the case. There were some rust spots on the trailing edge where I suppose water lifted up by the rotating dual tires had eventually caused rust, and I used Eternabond tape to cover those big spots after treating them with rust preventative.
Anyway, back in 2019 I’d done a lot of maintenance work and was able to get it running quite well again. It did have an annoying clatter noise from the outside fan as it started up but I couldn’t find what it was and eventually just let it ride. And for 7 years after that major maintenance work (cost less then $300), I only had a couple issues easily taken care of that I wrote up here on the blog. I’d used it full timing in very hot weather too so the thing would sometimes run almost 24/7, like when I stayed in Tucson.
But then in late April of 2023, suddenly, the AC just quit. Searching around, I found that the outside motor (condenser motor) had frozen up. Wasn’t until May that I was able to work on it. During the down time, I researched and debated different ideas on how to replace the heat pump with a newer more modern system. Like a mini-split. I eventually just determined that the best route for my situation was to buy a new Coleman Mach basement air system just like my old one.
I had tried to find just a replacement motor and it was $500, had no substitutes due to it’s odd 875/865 RPM dual speed design. I had tried to test the compressors but couldn’t determine if they would last much longer or not, and because the thing is so old, made in 2001 and here it’s 2023 (22 years old!), I felt that it was time to replace the entire unit. When I checked prices, wow, they’d tacked on a 48% increase since I checked it in 2019 as it was now $4000 (best price) when back then it was $2700. The actual inflation rate between those years was a paltry 16%. Sigh. Well, Hebron RV Parts had the best price with free shipping so I went with them, even with the excessive price.
I had pulled the old unit out from the basement and opened up the case and found a lot of compacted and loose dirt inside the outside fan & condenser area. Hmm. I guess using it full time the last 7 years did that, I had used it on the road while driving to cool the interior before I arrived at an RV park in the heat. I felt that all that grime and road oils may have contributed to the failure of the outside fan, but I wasn’t about to open the new Coleman to try to modify the design to give it more protection, didn’t want to void the warranty. The factory warranty is 2 years, and I plan on buying the extension of another 3 years.
Anyway, that’s the background, and here’s a few pictures and commentary of the installation of the new Coleman. Hebron used Old Dominion as the shipper and it arrived in a semi like this. In good condition, no shipping damage. Had it’s own wooden platform resting on top of another pallet.
The driver could only drop it onto my grass as there wasn’t a wide enough path on the cement. After unstrapping and uncovering, a couple neighborhood young guys lifted and carried it’s 275 pounds over to the work bench I’d made and set up right outside of the basement compartment it lives in. They’d also helped me move the old one out of the way nearby.
And this is the ratsnest of wiring the factory didn’t bother to dress. Really pisses me off to see a mess like this. It’s dangerous to the life of a machine to have it that messy. Terrible quality control. Or rather total lack of quality control. I’ll dress that wiring up later.
First thing I did was wire it up to AC and plug in the thermostat. Flipped on the switches and it started right up when the thermostat called for it without any odd noises or anything. Let it run for a couple hours to make sure that it’s okay. See that cardboard on the left? That was on the evaporator to protect it during shipping and I didn’t notice it for a while. If you get a new Coleman, be sure to remove that before install. It sucks air there so the suction can hold it in place blocking air flow so be sure to remove it.
This is the only damage I found on the unit itself. A smooshed palmprint area on the condenser. I have a comb so I straightened most of it.
Here’s where the 2 lines of 120 Vac come in. You can see where the circuit #2 wires are a bit too short. So I just swapped the two sets of wires routing #1 to #2 and then swapped the hots up at the CBs so the nomenclature would match. Now there’s little to no stress on the wires.
Another shot of the control wiring. What a mess. Terrible workmanship. And the worst thing? That bundle of wires right above that silver capacitor on the right side is traveling right on and next to and near the bare terminals on that capacitor. On a road traveling vibrating machine! A disaster waiting to happen.
A wider angle shot of the control panel wiring for future reference.
Getting to the actual installation, this is how the duct work attaches to the heat pump. I have to add some aluminum brackets to the output air hole in the side of the pump that holds this right angle piece of duct work. I just positioned it here to get an idea of how much room I had to juggle things around to make them fit.

And here’s a shot with that 90 degree bent duct work removed for a better view. BTW, that piece is special molded plastic custom made and designed just for this project and it would be hard to replace if yours is damaged so be careful with it. This picture shows the raw end of the venting that comes down inside the endcap that that custom 90 degree bend attaches too. I’d just finished repairing and taping up the raw end of that tube and this is the result. I used clear packing tape and when I finished I realized that that was a dumb move because I have an entire roll of Venture tape that I should have used as it’s resistant to heat and cold. Well, it’s mostly covered anyway so I hope that using packing tape won’t make any difference.
And here I’m using the old heat pump as a template to transfer the drilled holes in the case where the aluminum brackets attach, to the new heat pump. It pays to not toss things to early. I didn’t realize I’d need this as a template for a while.
A piece of cardboard aligned to where the duct tube would mount…
a few marks aligned to the screw holes…
And pilot holes were drilled into the Coleman, followed by self tapping machine screws taken from the old heat pump. I did eventually turn off power and remove those two armored cables for more work space. The zip ties tell me which goes to the #2 & #1 compressor terminals. 
And here using the 90 degree bend to adjust the position of the upper bracket. Once that’s installed, I’m ready to slide the pump into the basement hole. For those that haven’t removed their own heat pump yet, note that those brackets and the screws that hold this elbow are really difficult to get to if you don’t remove the rear bumper. I gave up and call it impossible. I suspect that at the factory, that bumper isn’t there when they install the heat pump so removing it makes sense.
Those two sheets of insulating foam just inside the compartment shown here go on top of the heat pump as it’s installed but before it’s cinched up to the top of it’s travel when the tray is raised. It would be impossible to get them in there after the tray is in position so make sure you get them in before raising the pump on that tray/rack.
And then I spent 1-2 hours trying to get the new heat pump all the way into the basement compartment. It just didn’t want to slide back against the return air molded plastic form that entirely covers the heat pump’s evaporator grill when it’s pushed back. That form has insulating foam tape all around the perimeter of the return air box (which is still in good condition) that is pressed up against the smooth side of the heat pump, makes a seal, and prevents outside air leakage into the return air system. I was trying to avoid using a pry bar where it might damage the condenser coils and fins or the case or the area around the control circuits so I was being extra careful. And took many breaks.
Eventually, I got the far end just started and in the right position, raised the tray with the big bolt a little so it would stay there under the lip shown below and then used a 1″x4″x3′ wooden stick to lever this near end back the final 1/2″. While holding it in place with the lever, I then grabbed my impact drill with one hand and quickly spun the 1/2″ bolt to lift the tray the pump sits on up higher. See that lip the pump is behind now? The pump has to be back behind it as shown here. That’s what it was so hard to get past, it was 1/2″ of trouble. The tray the pump sits on is lifted by two 1/2″ bolts, one bolt on either end accessed from below. So not easy to do it alone.
After I was able to get the heat pump in the correct position, then installed the 90 degree duct elbow pipe. Here’s what I did the last time with that vent as far as insulation to make a good seal. Instead of the poor open cell foam insulation that Winnebago used, I used the vinyl foam weather strip shown here. It held up well when I put it on in 2019 but had some damage and degradation that happens when pushed into place or removed so this time I put all new tape and put a 2nd row of tape right next to the first one, so I now have two rows of insulating tape all around the perimeter of the mouth of the elbow.
And here is the multiple rows of Venture tape I installed on the junction of the 90 degree duct with the duct work coming from the ceiling of the RV. I’d found a leak after my first install right at this junction and added a couple more layers to completely stop any air leakage. The leak didn’t show up for a couple days of operation so make sure you leave the back bumper off for several days to check if you do this replacement. So far the multiple wraps of Venture tape weather strip are working well as I don’t feel any leakage around that junction. I learned back in 2019 that the Venture tape does age out so that was one of my yearly checks…for any leaks in this outside section of duct work. I’m pretty sure that complaints about the Coleman not cooling or heating the RV enough is due to leaks here.
Here’s how it looks from under the RV looking up at the duct to pump junction. You can see the foam weatherstripping just peeking out of the seam. Making a good seal around the periphery.
And after it worked for a few days, it was time to dress this wiring. Of course, power was shut off and the thermostat control cable unplugged to remove 12 volt from the circuit board. What I did was find the best route for each wire and one at a time, unplug them, re-route them, then plug them back in. Preventing any issues from mis-wiring. This is the before picture.
This is just inexcusable for a $4,000 machine. Bad workmanship.
Here’s where all those wires contact the sharp edges of the terminals of the capacitor. A few months, perhaps years and there’s going to be a dead short there. Fire, smoke, flames perhaps. And a dead heat pump.
This was about as well as I could do with the dressing of the wiring. I’d have to open the case to do a better job. All the engineers would need to do to help matters is to move those two holes that pass wires into the condenser compartment on the right just above the caps up 1″! Then TRAIN the technicians to route the wiring better. And teach them that they can shorten wires that are too long so they need appropriate tools and supplies as well. The AFTER picture.
The loose blue and orange wires, in the lower space in the above picture, I disconnected from the old Coleman relays and I’ll use them to wire up those pigtails mentioned above. Right now they’re just hangin’, called flying leads.
Edit: Found the Winnebago wiring diagrams for the flying leads…
According to the correct drawing there for my Journey 36GD, the WHT/blk and ORN/blk wires downstairs inside the control section of the heat pump come from the load shedding circuit relay contacts and are wired in series with the power wire for the Compressor #2 relay coil.
So if the load shedding circuit senses that there isn’t enough power to run both compressors, it won’t allow the #2 compressor to run. In my RVs hallway is a control panel that has the thermostat, the tank level indicators, the genset hour meter and off/on start switch, and several other control switches. AND the load shedding device…Power Line EMS. That’s the device that controls #2 compressor relay. If I am plugged into a 50 amp 120V/120V power source, it just shows a green LED on for Comp#2, if I move to a 30 amp park, then that LED is off.
Here’s what a friend sent me about those flying leads in the thermostat cable:
“The Airxcel techs reply was:
“Rewire from old to new: Remove the compressor 2 blue wire from the PCB at the top, connect to the orange/black wire, then connect the white/black wire to the spot on the PCB that you removed the blue wire. The orange wire on the relay can be discarded.” ”
Continuing to dress the wiring better, I loosened the plumbers tape clamp on the caps and turned the far right capacitor CW a bit, re-dressed the wiring somewhat and that should work to prevent any of the wires going into the outside fan compartment from scraping on and shorting out to the cap terminals as none of those current carrying wires are touching the terminals like before.
And for reference, this is a shot of the wiring diagram from the backside of the control panel cover.
So that was the gist of it. The new heat pump is now installed, working correctly, and is working well. I still have some work to do with putting the bumper back on and buttoning up the basement compartment but that’s only an hours work. Right now I’m enjoying the cool air.
I will have to study the wiring diagrams for the heat pump and the thermostat to get the two pigtail wires connected but I’ll do that soon… done, see above. Pretty sure those wires are used when the RV is parked at a 20-30 amp only shore power situation. I’m at a park with 50 amp so it’s okay for now. Like they keep the 2nd compressor from operating without 50 amp but allow it to run otherwise. Controlled by the load center.