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Old 08-11-2010, 11:29 AM   #1
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Dash Air

When we left on our present trip north from Arizona the outside temp was 100 so the dash air as well as the front air were on high. When we left Utah we turned off the front air and then noticed that the dash air was not so cold. I took a reading with the lazer gun and got a reading of 74. Could that be correct ? Do those guns measure air ? If the reading was correct where do I look to fix the temp of the air? Do these units have a charge of coolant like home units ?
Wow, that was four questions in a row. Any or all answers will be most appreciated.
Presently we are at the FMCA rally in Redmond and don't anticiapate the need for the air for the next month but would like to solve this issue before it's needed. Is this problem worth standing in line for an hour to see a technician at the rally and does anyone know if they even address this issue ?
Thank you
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Old 08-11-2010, 02:59 PM   #2
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Lots of good reading about dash AC issues--problems and causes [fan controllers, wax valves, stopped in traffic vs down the road, etc]--on the forum...just use the search feature. I think the differential air temp for auto A/C is about 25 degrees [so an 80 degree day gives you 55 degree max A/C air] but dont quote me. Fact is, your dash air is going to have a hard time cooling your entire coach [huge heat sink] with 100+ outside temps [your car's interior-- perhaps/ your entire coach-- no].

PS--front genset slide design of Alpines seems to inhibit air flow thur dash fan at hi-way speed--IMO. So keep A/C on "Max" setting to improve air flow for both heating and cooling--believe it or not.
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Old 08-11-2010, 07:28 PM   #3
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Just like automotive air, in fact any auto-air repair outfit worth their salt can recharge you. I believe the recharge nipples are visible w/the gen slide open.
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Old 08-11-2010, 09:48 PM   #4
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You can also recharge the air conditioner with a DIY kit from Walmart, Pep Boys, etc. The fittings were where E-Mike says they are, easy to get to. Pretty cheap, and if it works even temporarily, it will save a bunch in repair costs. If not, not too much spent to try compared with what the mechanical repair will be.

But like Old Scout said, there are a number of issues with the dash air. Recharging is only one of them.
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Old 08-12-2010, 08:39 AM   #5
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I'm thinking the "max" setting should work similar to cars, recirculating cooler inside air, making the system's temperature drop more effective than cooling outside air.

The typical infrared temp guns don't measure air temps. They measure the temperature of material (e.g. air vent). The laser dot is a pointing aid. As the distance from the material and the temp gun gets wider, the area of the material being measured gets wider (e.g. you'd start to measure the air vent and the surrounding dash).
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Old 08-12-2010, 09:29 AM   #6
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Regarding the "max" setting, the idea of using "max" for cooling was intuitive to me--same as your car. However, I was shocked to find on cool/cold days that the hot air circulating thru the dash at hi-way speeds seem to be restricted [eg, at hi-way speeds, I had the fan on a higher setting to get heat, then when we slowed to go thru a town, we got cooked].

I started leaving the setting on "max" and most of my spousal unit's "issues" with the dash heater went away. Not sure what operating the dash heat on "max" setting means for the overall system in cool/cold weather--dont think the A/C compressor is running if the system is not calling for cooling. Thoughts?

PS--Ive tried both the Wal-mart re-charge can and even tried the full-blown solution with borrowed guages, vac pumps and reams of internet instructions. Ive managed to replace a leaking hose and a compressor but always walked away questioning things like freon pressure Vs ambient air temps vs inside cabin air temps???.

Perhaps I am making it too hard but I find that regular automotive A/C "experts" are often confussed by MH configurations [fan controllers and wax valves] and RV A/C "specialists" dont always seem to the "sharpest tool" in the shop.

Note: most/all Camping Worlds wont even work on the dash (auto) A/C. So what do they know that we dont?
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Old 08-12-2010, 10:31 AM   #7
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Max setting is as described- it resets the dampers to draw make-up air for cooling from the cabin only. I usually default AC to Max in the moho. I figger there is an effectively unlimited air supply in the cabin, so no need to sweat whether the recirculation will get stale as in a small passenger vehicle.
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Old 08-12-2010, 07:40 PM   #8
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Chris Cross - 74 degrees is not a good temp out of the A/C registers. When aiming the IR gun at them you should be reading the register temp if it has been running for awhile and has stabalized, which would also be the air temp just before leaving the registers. The guns I have used are very accurate. The air temp leaving the registers should be about 45 - 50 degrees.
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Old 08-12-2010, 10:32 PM   #9
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So ambient air temp doesnt affect A/C air temps--hum?
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Old 08-13-2010, 08:38 AM   #10
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I just added a can of Freon. The AC had not been used for a while and the pressure was so low that the compressor would not run. I added a small amount of Freon and the compressor switched on. The side fan motor does not run when the engine is cool, so I sprayed water on the condensor coil to test the cooling. I will measure the pressure again to see if it has leaked.
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Old 08-13-2010, 08:57 AM   #11
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In addition to ambient temps, freon volume and pressure, and fan controllers; did I mention PAG oil volume. If you start from scratch [presume this means having "flushed" the system], 2 oz of PAG is recommended. If you are topping off freon after a suspected leak, you really dont know how much PAG is left in the system--too little and you fry the compressor; too much and you coat the evap coil and compromise heat exchange. Then there is the evap/drier tank--when do you replace it and where to you get one? Can you tell this is one of my favorite subjects--my dash system is currently working "OK" so I ain't messing with it!!!!
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Old 08-15-2010, 12:46 AM   #12
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All - First the difference between the incoming air and outgoing cooler air is called the Delta T Split. The best I have ever seen on a dash air or even a roof unit is 23 Degrees, and that was a carrier unit. This differences it always around that figure, some better by a little, some worse by a little. Residential units might be a tad better, but not by much, as you can only do so much to air to cool it. Mostly you are removing the water in the air.

There is a tag on the a/c system someplace, which tells you how much oil versus Freon (or chemical used as coolant medium) is in the system. Any a/C mech worth his salt will check this tag, prior to doing any addition of oil or Freon to a system. Speaking of Freon, several different types were and are used in different types of a/c systems; the tag will have the type you need to use if replacement of it is necessary. Don’t substitute one for another, it will break the system, and it won’t be repairable.

Next and BIG issue, all outside air has moisture in it; this moisture is VERY bad for an a/c system. SO, when you charge the system, the best way, is to empty the system first, then pull a vacuum on the system for at least 4 hours to ensure that you get all that moisture out of the system. You need a very sophisticated vacuum pump to do this work. Harbor freight sells several; buy the best one if you plan on taking up this line of work. The alternative method, is to use a gauge set (comes as a two and three set-use a 3 gauge set even though you won’t use the center gauge unless you are taking a vacuum) and add Freon to the system in a measured amount, but as mentioned, you won’t know if any of the oil has gone out of the system, so you might not add some when needed, and you might add some when not. Both will again screw up the system, and it again might not be fixable.

Now back to not doing the above and all that moisture, will create a very corrosive mixture in the very fine diameter tubing which makes up the a/c system. This will cause the tubing to either clog up, or corrode through, which is another VERY bad thing.

Now, the internet is a wonderful thing, lots of information out there, but, if you are going to work on a system on your MH, and don't know how it works, or have never worked on it before make sure you get several sources of information before you do the work. You can call any residential a/c shop and they might give you an overview on what you need to look out for. Or you can try to find a “CERTIFIED” RV specialist to do the work. Since less than 5% of all RV repair techs are classroom trained with the associated hands on to go with it, and certified, you will find that hard to do. Next, lots of RV places say there techs are “RVIA certified”, and all that means is the person took a test consisting of 150 questions, after buying the text books online for 400 dollars studied them, and passed the test. It also could mean, the tech attended RVTC, and as part of the final exam choose to take the RVIA exam as well. Just having the RVIA “certified” does not mean that person has any training other than learning from someone else who learned by someone else who might have hands on by someone else who may not have known the proper and safe way RV repair should be completed. It does not mean he/she has been trained in any system on an RV. Some community colleges provided an 18 month to two year training session, many folks who took some of that training never finished, or gave up when also having to take English 101. In this economy there are only two places currently teaching and certifying RV graduates. RVTC in Largo, FL and RVSA also in Florida. Camping world closed their RV College 18-24 months ago when the company was purchased by another outfit, and sent the students home, then almost got sued, and at least completed that class. I cannot speak for those students’ capabilities. I can speak for the RVTC Students since that is where I attended. I carried about an 90 average and passed the final as a master tech. So I sort of know some of the issues contained in RV a/c units. Car a/c units are some different, which is what the front dash unit in alpines and many other MH are made from. However, even that is different, because of the distances involved from the back of the coach to the front of the coach, etc. Since I am a certified RV Specialist, and have had classroom and on hands training in a/c's I am well aware of the pitfalls in someone doing a/c work, who don't know what the heck they are doing. You also have fallen into the pit, common to many folks whose neighbor, who is an expert at everything, tells you!!!!

Hey bud, it just needs a little shot of Freon to get it working, and this same fellow is also the fellow who burned his coach down the next week, because he got his 120V electric mixed up with his 12V.

Now many on this forum have engineering training, and other types of background which lends itself to repairing RV’s and working on AC units. My comments above are not meant to disparage that knowledge. But, my strong caution is, if you don’t know what you are doing, don’t touch anything unless you are prepared to possibly replace all the parts and pieces because you did something wrong. And trust me, the piping from the back of the coach to the front is long and complicated, and some of it you cannot get too. Know what you are doing or find someone who does to fix it.

And I am really trying to save you bucks, because I am currently charging 50-95 dollars an hour, and people are paying me to work on their RV’s. Sorry to be so long winded, but I am really trying to save you more trouble down the road.
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