Try this first before you buy 2nd AC unit or bring your unit in for AC service.

[halfprice]

Hmmmm. Some new people here like to criticize others that have been a valuable member for a long time helping many members along the way.

Point is there are many opinions on how things work. Everyone has the right to their opinion and they shouldnt be criticized and/or insulted for expressing their opinion

I am done now.

Jerry

[Long & Winding road]

Originally Posted by Chance

A significant portion of the A/C’s rated capacity is used to remove moisture from the air. You’re correct that measuring temperatures alone doesn’t tell the entire story. When tested for certification, these A/Cs are operated under controlled conditions which includes relative humidity.

One thing that is a CERTAINTY is that when A/Cs are operated at lower evaporator pressure/temperature, they will require more power per amount of cooling; assuming everything else remains the same. The compressor has to elevate the refrigerant from a lower pressure up to the condensing pressure. That means lower A/C thermodynamic efficiency. You also lose overall cooling capacity.

Im sure your right.... my ac just pours out the water all the time. But is humid down in AR and that is on par with my home and cars.

How are we "loseing overall cooling Capacity" when its cooling the RV down better now than ever in my case? Or are saying that "over time" we are going to kill the AC unit because we are forcing it to work harder than it should?

Perhaps your right.

If the avg RV AC unit lasts 10 year but you only see 82 - 85 at best in the hot part of the summer but with the mods you can get 72 - 75 deg and it only last 5 or 6 years I would NOT be too upset. Now only two years of life.... that would suck.

If your happy with your AC cooling your RV in the summer time than great. This tread is not for you.

If your NOT happy with your AC cooling and you want to "try" a few tips and tricks BEFORE you spend money to either "fix" your AC unit OR BEFORE you add a 2nd AC unit than great.

It not like I'm trying to get the AC to put out 25 deg temp - if so im sure something would go wrong. All I want to do is have my AC cool down my rig like it should. All I expect is consistant temps in the mid 70's. Sure if its 115 outside it might be 80 inside and if its 75 degees outside It might be able to cool to 60 inside. But at 95 deg I want around 75 degree temp inside - and right now Im able to do that or even less.

I want everyone to go purchase a small RV temp gauge and test their output temps this weekend and post here. They only cost like 6 bucks.

That way we can see what the average is. But we need to note which brand AC, BTU's and the # of AC units we are running.

Cant wait to see the results.

[Long & Winding road]

Originally Posted by halfprice

Hmmmm. Some new people here like to criticize others that have been a valuable member for a long time helping many members along the way.

Point is there are many opinions on how things work. Everyone has the right to their opinion and they shouldnt be criticized and/or insulted for expressing their opinion

I am done now.

Jerry

Exactly, thanks for that. Im just trying to help folks that NEED the help. Not debate every little thing. If it works it works who cares why.

[halfprice]

Yep help is appreciated by everyone

[gmtech16450yz]

Originally Posted by halfprice

Yep help is appreciated by everyone

Help IS appreciated by everyone. My point was some people only like to shoot down theories and ideas. It was just bugging me when I try to encourage people to think outside the box and experiment to learn new things and somebody keeps jumping in basically saying we're all wasting our time.

For me it was simply a matter of conveying information in a way that leans more towards encouragement vs. discouragement. You can provide information or "help" in both ways. I just try to live in a positive place instead of the negative approach of telling people all the reasons why something shouldn't work.

Back on subject, the idea of an AC system "not lasting as long" because the temps are 10 degrees higher or lower is (IMHO) ridiculous. Believe me, DO NOT WORRY about taking years off the lifespan of your roof AC by doing something like moving your temp probe. How long IS the lifespan of a roof AC? Not trying to be a smart@ss, but the average lifespan of a roof AC is probably a lot longer than what most of us on this forum have left in US. There are way more things in life to worry about that are just a tad more important than how long your AC may or may not last.

I hate to go back to what I was trying to say about negative vs. positive help, but the comments about "reduced thermal efficiency" and "losing cooling capacity" are perfect examples of scaring people with "help". Are those statements fact? I honestly don't know or care. I do know that bringing up statements like that DO NOT encourage experimentation and innovation, they just instill fear and uncertainty in the people you're trying to help. A post like that is a Passive/Agressive way of saying "What you're trying to do is stupid and I'm going to come up with technical bs that makes you question what you're doing." Is that the kind of help you guys want?

[halfprice]

I get your point and agree with most of what you say. But for the most part everyone in this forum get along very well and it just bugs me when I see the insults coming out. Especially when the person is trying to help. Theres just no need for the insults.


Have I agreed with every comment made, no. Are there some people that I ignore yes. I just like to read the posts without the bs.


So lets get back to the mods. Ill be insulating the acs on the roof, and the copper pipes, plus ill remove the inside panels to look for leaks. Not sure if ill move the probe yet.

I have the coleman mach 3 15000 and 13500 The last time I checked temps inside was 78ish and both were pushing out 53* Temps are a lot hotter here now so Ill post new temps when I check Maybe tomorrow.

Plus Ill check temps after the insulation is installed.


Jerry

[carlgorski]

Originally Posted by gmtech16450yz

Ok so I did a little testing for you... haha.

With an infrared heat gun it does show that the temps at the top of the evaporator are colder. It's not super accurate because I was shooting the thermometer at an angle since it wouldn't fit all the way inside. I didn't take the unit apart to verify which end the high and low side lines come in though. That would tell you exactly what areas of the evaporator will be colder. I've had AC evaporators freeze up, if I remember right they mostly freeze from the center and the edges are last to freeze. I've had aftermarket AC's stop all airflow and turn into a giant ice cube inside. No big deal, you just turn it off until it melts.

The edges of the core showed warmer, which makes perfect sense. Putting the probe at the absolute edges of the core could be a good idea.

I've ran mine for about 2 hours straight with no compressor cycling and it didn't freeze up. About a 90 degree day, entire coach in direct sun, inside coach temp was down to 67 degrees, (!!! It was pretty d@mn cold!) and outlet temps were in the very low 40's.

Your question about running it "all day- 10-12 hours" is my (and yours too) point in all this. If you have to run your AC non-stop all day long with no cycling to maintain a decent temp, something is wrong. It seems to me that Coleman is pretty conservative on their evaporator icing prevention strategies. I think they're cycling the compressor at temps that are way too high. Someone in this thread quoted Coleman's inlet and outlet temp specs, it's pretty weak actually as AC systems go. Automotive systems are much stronger of course, but getting ~40 degree outlet temps on a 100 degree day usually isn't a big deal. The "testing" specs on these RV units says something like a 20 degree temp drop is "normal"? F that. That's pretty weak.

My point is that you should NOT have to run the AC non-stop for 10 or 12 hours to maintain a decent inside coach temp. And if it's that hot and your (not "your" specifically, I mean everyone's in general terms) RV has that much heat loss, that means the AC's input temps are going to be way too hot to get the evaporator to freeze up even if you pulled the temp probe completely out of the core.

And yes, I have my temp probe (thermistor) hanging in the airflow in front of the evaporator, up inside the AC unit. I basically just wound it around the harness coming from the control module inside the inlet area.

For you other guys reading this, TRY IT. It's a totally reversible mod that takes about 2 minutes to do. There are tons of people on here complaining about AC performance. You've got nothing to lose trying this and it might just fix your issues.

I just put a link to this thread in the other AC thread talking about adding a vent. For those that try moving or removing the temp probe, remember that MORE airflow is better. Open ALL the outlets. Lack of airflow is what makes evaporator temps get too low.

Coils on roof?

[Long & Winding road]

Originally Posted by carlgorski

Coils on roof?

NO, inside RV. Take plastic cover off (like 6 screws - 4 on the main cover and 2 on the air diverter cover) and you will see coils on the front side of the RV and them temp probe is the single wire (mine is white) that goes into the coils.

[Long & Winding road]

Remember the whole point of this post was "Try this before you buy a 2nd AC unit or bring your unit in for AC service". My AC was Terrible before but now Im very happy with it.

I already had my RV an appt (a few weeks out) at CW when the guy behind the parts desk said "Did you try moving the probe" so I asked him a few question. That led me to do research on this subject and I found that many folks had air leaks in the box. Then I thought Why not insulate the top part after I felt the heat with my hand on the black AC cover on the roof.

Afterward I saw the results of my mods I cancelled my CW appt.

These mods may work for you - may not - but for the little time they take and very little money for the insulation I felt they were worth the shot.

[gmtech16450yz]

Originally Posted by Long & Winding road

Remember the whole point of this post was

The whole point of your post was awesome! It's why I come to forums. You learned something and shared what you learned with us all. I LOVE IT! I'm all about learning and sharing, it's my favorite thing to do in life. I spent my entire career being a mentor to hundreds of techs, they were always grateful to learn what I knew, but they didn't always realize I learned a ton from them in the process. And a lot of the time what we were both learning had absolutely nothing to do with our job.

I think I spent more time as a therapist than an auto mechanics mentor actually! I once asked a guy I worked with what he'd do if his son came home and told him he was gay. The guy immediately replied to me... "I'd kill him!". He wasn't kidding. Many, many hours of discussions on that particular
subject over many years of working with him changed how he'd answer that question today. I learned more about human nature (one of my favorite subjects) and he learned to be more understanding and compassionate about things people have no control over.

Anyway, thanks for sharing. I'm sorry I derailed the thread a little bit. As you can see, I'm pretty passionate about encouraging learning and new discoveries that often come from thinking outside the box. I'm probably a little too sensitive when I feel new discoveries or learning is possibly being threatened by anything negative. I'll try to be better!

Sooooooo, I'm actually going to do what you've been begging people to do! (Actually others have been asking for the same data, the actual delta between inlet and outlet temps.) I'm going to put a digital thermometer in the inlet side, and another one in the outlet side. We're going to the lake this weekend, I'll have plenty of opportunity to run the AC in hot weather. I'll try to test it both ways, with the probe in the original/stock location and with it hanging free. Hopefully I'll have some data for you and others here.

BTW, you don't have to take out a single screw to move or remove the probe. Simply take the vent cover and filter out of one side, reach up there and the probe is right there. Moving or removing the probe can literally be done in less than a minute with no tools.

Like your title said, this is an issue that effects many RV owners to the point of thinking about buying a second AC unit. I also believe that ANY help you can give these AC units by trying a few mods would be beneficial and worthwhile. The design of these units are decades old. Honestly, Coleman doesn't really care or would want to invest any money into re-designing these units to work better. There's no reason for them to. So I absolutely believe there is room for improvement on the design and efficiency. I thought that 25 years ago actually, and learned something super cool (ugh) in the process. Let me post this and I'll blather in another post...

[halfprice]

Remember guys when you use temp probes dont let the probe tip hit or rest on the inside of the ac unit. If it rest on something you might only get the temp of the metal or plastics its on and not the ait flow going in or coming out.

I only have bbq temp, Themopen, but they are very accurate. I have to hold the temp probe in front of the vent to get a proper reading.


Jerry

[gmtech16450yz]

This is the discovery I made about 25 years ago on improving the efficiency of these RV roof air conditioners...

We had a 19' Tioga Class C. We absolutely LOVED that thing, it was amazing. We logged over 150 separate trips in it, the Dodge powertrain had over 200k miles on it when we sold it. It didn't come with a generator or roof air. It was built in '73, most RV's didn't have either of those things stock. It didn't have room for anything like an Onan, I actually had to take the propane bottles out of a compartment and install a single propane tank underneath to have room for even a tiny portable generator.

I took a portable Yamaha generator, a 600 watt max unit, and built it into the compartment. Everyone that saw or heard what I was doing said I was crazy. 1- You can't permanently mount a portable generator in an enclosed cabinet. 2- It's WAY too small to run the Coleman roof air I had just put in it. 3- You'll never be able to run a portable generator while driving down the road. 4- The roof air is going to burn up from improper voltage/ amperage. 5- The generator is going to burn up from lack of airflow. 6- The motorhome is going to burn up from having a gas tank inside a closed compartment.

So yeah, I ignored all that and did it! Ducted air into and out of the compartment, ran fuel line from the motorhome gas tank, built a super quiet but more efficient exhaust system for the generator that exited outside the compartment, and wired up a transfer circuit into the coach. It all worked awesome but as I expected, the amperage output of the generator was right on the cusp of tripping it's circuit breaker when the roof AC was used.

So I worked on increasing the power of the generator and reducing the power draw of the roof air. My mods made the whole system work great, except for in extreme conditions at times. Fast forward a few years and we're on a trip through the Utah salt flats in the middle of a super hot summer. I had noticed that the AC and generator would work fine when stopped, but when we started driving it would trip the breaker because the amp draw of the AC was too high. I had my wife drive while I watched my ammeter I had wired into the generator output. The amperage was fine when stopped, but kept rising once we started moving. We pulled over at a rest stop in the middle of the Bonneville salt flats and I literally climbed up on the roof and took the cover off the AC!

I looked at the way the system was designed and was a little shocked. It's backwards!!! The condenser is at the back of the unit, the fan pulls air from outside the rear of the unit, through the condenser and then out the sides. So while at a rest stop in the middle of Utah, I pulled the roof air off, rotated the entire unit 180 degrees, and bolted it back down. (Yeah, I'm just a little crazy.) My wife gets behind the wheel and starts driving while I'm in back watching my ammeter. OMG my theory was right, the amperage started DROPPING as the RV got going faster!

From that day, our AC unit on that old Tioga was mounted backwards. (Backwards according to how Coleman said to mount it and how 99.9% of roof air conditioners to this day are mounted.) It was always more efficient when driving, and the efficiency when stopped didn't change a bit. We used the cr@p out of that generator and AC system until we sold that RV a couple decades later.

So sorry for the rambling post, but it's VERY relevant to this thread and it's good info for anyone that has issues with AC performance while driving. To this day, RV roof AC units are still built in this inefficient way. Why? Like I said, they're selling plenty of them, why would they bother spending money re-designing something that sells? Lots of people don't even believe you're supposed to use the roof air and generator while driving! It's just a perfect example of thinking outside the box. Sometimes something that sounds crazy ends up being not so crazy.

Here's a pic of our old Tioga. If you notice the roof AC, it has extra vent holes cut into the front of the cover. I originally just turned the entire unit and cover around. Later I modified the cover so it looked like it was mounted properly, but the inside unit was still mounted backwards, condenser in front so it could suck in all that fresh air. Actual, factual data from before and after amp readings and years of verification proved that the crazy idea I had at a rest stop in Utah was valid. Don't EVER let anyone discourage you from pursuing crazy ideas!

[Long & Winding road]

Thanks GM Tech and half price for your input and stories.

I love this forum.

This AC mod I did worked so well it compelled me to sign up to this forum and tell everyone about it. I felt it was too good not to share since I never saw any postings about AC mods before.

I been reading only on this forum for about TWO years now (A year before I purchased my 17 Axis and the year after). I have learned so much and have completed numerous mods and upgrades that my fellow forum members have wrote about. Thanks again.

[halfprice]

First temp reading with no mod. Coleman mach 3 15000. 91* intake but quickly dropped to 89* output 59* so 30* drop.

Now im going to remove the inside panels tape any areas that i think need it and maybe move the probe.

Ill be vack

Jerry

[halfprice]

Moved the probe up 1-1/2" now tge coldest it get is 61* thats going in tge opposite direction

[Long & Winding road]

Originally Posted by halfprice

First temp reading with no mod. Coleman mach 3 15000. 91* intake but quickly dropped to 89* output 59* so 30* drop.

Now im going to remove the inside panels tape any areas that i think need it and maybe move the probe.

Ill be vack

JerryAttachment 11587

Wow, thats not bad. But I bet you can make some improvments. Let us know your outcome.

[halfprice]

Originally Posted by Long & Winding road

Wow, thats not bad. But I bet you can make some improvments. Let us know your outcome.

I agree but i thought 40*+ was easy to get.

[Long & Winding road]

so your saying your getting 59 to 61 on your output temp? Try some of the other mods and let us know. I started out around 65 deg but my probe was 1 inch from the bottom. Did you move your probe up already? or is this picture the "Before" Pic?

[gmtech16450yz]

Originally Posted by halfprice

Moved the probe up 1-1/2" now tge coldest it get is 61* thats going in tge opposite directionAttachment 11588

Pull it out and put it in a glass of ice water.

lol. That's what she said.

Seriously. Try putting the probe in a glass of ice water, and then in a glass of hot water. I really think the first step is to understand how exactly the probe is working. If you can determine the exact water temp the probe reacts to as far as compressor cycling, then we're onto something. And compressor cycling might be (is) totally separate from thermostat cycling you know. If you don't have any way of monitoring amperage draw, you might be able to hear a change in compressor noise or vibration when it's running.

As far as moving it an inch and a half and getting a change from 59 to 61, I'd almost call that within sample variation and not really conclusive. (NOT being snotty, just trying to help.)

[Long & Winding road]

Make sure the probe is touching the coil under the allumimum fins. Insert between fins then slide down until it stops.