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Old 07-07-2018, 11:24 PM   #1
Long & Winding road
Senior Member
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Brand: Thor Motor Coach
Model: 2017 Axis 25.4
State: Arkansas
Posts: 2,446
THOR #12231
Try this first before you buy 2nd AC unit or bring your unit in for AC service.

I been wanting to share this for 4 weeks so I finally joined the forum today so I can share some of my success stories. This is my most satisfying (and cheapest) so far.

This might be a bit long winded for my first post but I wanted to tell the entire problem and my solution so please read along. I have read about this same exact problem 20 times + on this forum so I hope it helps others. It might save you $800 - $1000 over installing a 2nd AC unit so might be worth a try - you decide.

I will "try" and keep my other posts about my other mods more brief. (I said "try" LOL). And before you ask I will try and post some pictures later.

When I purchased my 2017 Axis brand new the 15000 BTU AC was not cold enough and was driving me crazy. The best it would do was around 85 - 87 deg inside temp after being on all day in the hot sun (95 deg + outside) while driving or parked at the “trail head” (Mtn biker here). At first I thought it was not the AC's fault and I fitted all of my windows with bubble wrap like I read on this forum (thanks to Jerry' Hurricane Mods and many others), added the extra AC cold air vent on cover, then inserted roof vent foam inserts to block all the heat that I could. That helped some (Maybe 82 deg at best) but not enough and took forever to get down to this temp once the RV heated up.

So right before I had a few things done on my punch list this spring (but after I fixed 20 + items myself first) one of the Camping World employees at service desk gave me a useful tip (imagine that- LOL) that I have NOT read on ANY forum or in any of my many searches on this subject.

He said to move the temp probe ("Thermistor probe") up a little to see if that would help but not too much so the unit don’t frost up. So after researching on that topic for a few weeks I thought I would try a few things myself before I have CW tear into it.

At first I decided insulated the AC box (on roof) really well with left over Dynomat and Frost King duct insulation (I did the entire aluminum ductwork under the plastic cover on roof). Then I used the foam rubber pipe insulation on the exposed AC copper pipes to prevent frosting up. Left it like this for a week or so - This helped some but I was really doing this to help with the 2nd mod I was planning. So I took out my automotive AC thermometer and stuck it directly in the cold air path inside RV at AC cover - it was reading about 65 deg. Small improvement (but im not sure by how much since I didn’t take a before temp – sorry).

For 2nd part of this job I removed the inside cover and used aluminum duct tape to seal up leaky ductwork and added some half inch soft foam to insulate between cover to the duct work (many small leaks - im sure this helped a lot - check yours now!).

3rd part of AC mod - I moved temp probe up about two inches or so. Make sure it contacts the coil inside fins by slide it in and then down slowly until it stops at coil. You can see this probe on the cold air return side (this is inside the RV looking up for a single white wire with metal probe stuck in the aluminum fins about one inch from the bottom - which by the way is the location the manufacture recommends - I checked. So this might void your warrantee (move it back before AC service?)).

Now tested the cold air duct again and it was down to 55 deg! I tried it out for a day and I was able to get the inside of the RV down to like 76 deg or so. Big improvement. But the next day I thought "we can do better" and "My car AC show 35 deg at the vents why only 55 deg on the rv?" so I moved the probe up another 1.5 inches (about 4 inches total – which was about the max you should go according to my research – make sure you do your own research.) and then I checked with my temp probe - It was 45 DEG NOW!! Wow. I thought that was great and I better leave it alone - don’t want to frost up the coils or screw something else up.

Final results = 75 temp in inside of RV now on 90 - 95 deg days sitting in full sun!!!! And that’s WITHOUT BUBBLE WRAP on windows!! (70 -72 in shade).

And 70 – 73 degrees in full sun with my new “ceramic window tint” (that will be a later post – highly recommend).


I been testing it for a few weeks now before I posted this so I knew it worked well and has NOT frosted up on me. I even went on the roof to check coils/pipes after two hours full blast and not one sign of frosting up, then I check again at 4 hours - looks normal. I also removed inside cover and looked around - no frost – even on hot humid days.

We did several day trips (and one weekend) with AC unit on for 2 - 5 hours at a time and it worked perfectly. And on the 4th of July it was on for 10 hours straight and worked perfectly the entire time.

So now when turn on the AC and the RV is hot inside (90 - 100 deg!) in 45 minutes its down to 82 - 84 deg next to kitchen sink (were I keep a digtal gauge) and 72 - 74 deg in 1.5 - 2 hours! The thermostate is in the bedroom and it will show about 2 - 3 degrees warmer temp then the kitchen. Eventally it will equalize temp with all roof ducts open. It has not problem maintaining 73 - 75 deg at any given time with door opening up some and windows not covered or shade pulled down (after my window tint) or driving down the road on a sunny days. Its been realativly cool this year (90 -92) so if its 100 outside Im sure my readings will differ some.

My 4th AC mod was installing he Coleman Mach digital thermostat (I highly recommend). Really make the system work well.

I hope this helps a few of you guys either suffering with inadequate AC units or thinking of adding a 2nd AC unit.

I hope I didn’t bore you on my first post - I thought I should explain it fully so you can decide if you want to modify yours. Im not telling you how to do it – just telling you how I did mine and you take full responsibility if something goes Wrong.

Happy trails
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