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Old 07-30-2018, 08:32 AM   #1
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AC Delta

What are you guys getting for your delta across your AC coils? And where/how are you measuring?

We have 2x11K units in our Greyhawk. DW thought the front unit wasn't working as well as the rear. So I measured. I let the ACs turn on and "warm up" for a while (maybe 5-10 minutes, they had been running already, this was not a "cold" start test) and measured the air going into the unit, then measured the air coming out of the dump vents on the side of the unit. I used an IR gun-type thermometer from Harbor Freight, so not terribly precise, but should be able to handle deltas easily.

I got around 10-12 degrees on the front unit and 12-15 degrees on the rear unit. This seems low to me? Our camper does cool off enough to be comfortable, even in full sun up into the mid-upper 90s. They'll run non-stop all day, but they will cycle at night.

I'm going to try again next time I have the unit home, and I'm going to be a bit more "scientific" about it, but I just wanted to see where everyone else is?

And then my next question will be whether there's anything that can be done about it? One thing I will likely do is change out my cowls up top from black ones to white ones, and I'll insulate the outside of the cold side of the roof unit. I've already checked out all of the registers, and I've worked on the inside of the units making sure it's all sealed up correctly, and it is. About the only other thing I can do there is actually tape the partition between the return and output sides, but it is currently sealed as designed on both units.
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Old 07-30-2018, 09:12 AM   #2
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A bit off topic: Did you also use that IR thermometer to find the sources of heat inside?
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Old 07-30-2018, 09:16 AM   #3
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There is a thread on here of a method of adding thermofoil insulation on the top and vents to insulate and seal any sources of heat loss. I did it last year and have not decided yet if it was worth it.

We will be out for a couple of weeks in August, I will do some checking with my Ir thermometer.
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Old 07-30-2018, 09:27 AM   #4
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Quote:
Originally Posted by oldmanAZ View Post
A bit off topic: Did you also use that IR thermometer to find the sources of heat inside?
I'll say that's on-topic overall.

No, I have not. Most of the major sources of heat I have, DW is not allowing me to do anything about. She DID allow me to put Reflectix in the skylight, and that made a pretty big difference. Other major sources of heat include basically all the windows, the cab, the door, etc. DW does not want me to put Reflectix in those openings because she thinks it looks "trashy". I do have quite a lot of tint left over from when we tinted the windows in our S&B house, and I intend to use that in the MH. The windows are already tinted, but this extra layer should block out more UV and heat. Most of the time we also put a "mask" over the cab of the MH, and that helps as well. If we do that, in addition to bulking up the "curtain" that divides the cab and the chassis, I'm betting we can block A LOT of heat.

Slide toppers are also on the short-list of mods, and that should help with the load from the tops of the slideouts, even though those are somewhat insulated with overhead cabinets.

Anyway, I'm also discovering I may have some heat sources under my bed as well. So next time I have it in the driveway (should be week after next) I will take an exploratory walk around with my temp gun and see what I can see.

Like I said, the rig DOES cool off, and the units WILL cycle, it just doesn't seem to be as efficient as it should be?
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Old 07-30-2018, 02:05 PM   #5
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Bob, our two 11k units work about the same as yours. The bedroom seems to work better but it’s misleading.

The window load is almost nonexistent in the back compared to the front.

What we do is set the thermostat for front and the thermostat for rear at about 5 degree different. Doing this seems to help equalize the temperature front to back in the coach. (Set thermostat 5 degrees lower in front)

I’m not sure you can check the delta on a RV unit like you can on a home or commercial one. I just measure the temperature coming out of the cover vents.
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Old 07-30-2018, 02:14 PM   #6
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I did remove Outside cover and covered all the surfaces with reflectix
Also sealed all small air leaks and made sure Airbox divider was sealed and in Place.
Overall the unit is much cooler,
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Old 07-30-2018, 02:38 PM   #7
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Quote:
Originally Posted by Camper_bob View Post
I'll say that's on-topic overall.

No, I have not. Most of the major sources of heat I have, DW is not allowing me to do anything about. She DID allow me to put Reflectix in the skylight, and that made a pretty big difference. Other major sources of heat include basically all the windows, the cab, the door, etc. DW does not want me to put Reflectix in those openings because she thinks it looks "trashy". I do have quite a lot of tint left over from when we tinted the windows in our S&B house, and I intend to use that in the MH. The windows are already tinted, but this extra layer should block out more UV and heat. Most of the time we also put a "mask" over the cab of the MH, and that helps as well. If we do that, in addition to bulking up the "curtain" that divides the cab and the chassis, I'm betting we can block A LOT of heat.

Slide toppers are also on the short-list of mods, and that should help with the load from the tops of the slideouts, even though those are somewhat insulated with overhead cabinets.

Anyway, I'm also discovering I may have some heat sources under my bed as well. So next time I have it in the driveway (should be week after next) I will take an exploratory walk around with my temp gun and see what I can see.

Like I said, the rig DOES cool off, and the units WILL cycle, it just doesn't seem to be as efficient as it should be?
when they replaced our house air conditioner he stated disconnect the "energy saver switch" it shuts of and turns on the air whenever the power company feels like it.. which causes the compressor to shut down hard.. then start back up over and over ... then I said how about a bigger unit 3 ton instead of 2.5 ton.. he said you want it to run all the time.. it draws out the humidity so you don't have the cold and clammy air... the 3 ton would cool faster but wouldn't draw out the humidity.. made sense and I can say I am very happy with the current performance.. My guess is the air conditioners are the same for the campers... they will run all the time and as long as they can hold the temp you should be good to go and you won't have that cold clammy feeling... or it was all just mumbo jumbo...
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Old 07-30-2018, 04:37 PM   #8
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Quote:
Originally Posted by cabinetmaker View Post
Bob, our two 11k units work about the same as yours. The bedroom seems to work better but itís misleading.

The window load is almost nonexistent in the back compared to the front.

What we do is set the thermostat for front and the thermostat for rear at about 5 degree different. Doing this seems to help equalize the temperature front to back in the coach. (Set thermostat 5 degrees lower in front)

Iím not sure you can check the delta on a RV unit like you can on a home or commercial one. I just measure the temperature coming out of the cover vents.
Yeah, between the window, door, cab load up front, and comparably minuscule heat load in the bedroom it does create a "feeling" of not working as well. Between that and the large difference in cubic feet being serviced, those are some significant differences between those environments. That's what I told DW from the beginning. I've already been tinkering with the settings and how I balance the vents. Since they're both ducted together, the rear unit can actually help the front unit. As an aside, I wonder if 30A could service a 13.5K unit in the front with an 11K in the rear; that would make more sense.

That's how I measured it too. I hit the temp on the intake at the cover, and took another reading on the output at the cover.

Quote:
Originally Posted by katiedog View Post
I did remove Outside cover and covered all the surfaces with reflectix
Also sealed all small air leaks and made sure Airbox divider was sealed and in Place.
Overall the unit is much cooler,
I did that on my trailer. We had a 30 ft trailer with a super slide being serviced by one 15K unit (2nd AC Prep, and I was going to install if we kept the trailer). Anyway, I went around finding any and every small improvement I could find, and over all of those tiny improvements, the unit performed better overall.

I guess it makes sense to attempt those same improvements in the MH. Like I said, I've already dug into the ducting and the sealing inside the unit; it all looks pretty good. Now I'm going to get up on the roof and check that out.

I think I'm going to use something other than reflectix on the outside unit this time though. And I just can't see how black covers on these AC units makes ANY sense at all. If it were me, I would avoid putting ANYTHING dark in color ANYWHERE on the unit, especially those areas that have to do with keeping the motorhome cool!

I'll post a writeup in a new thread and add it to my continuing "new unit" thread as well whenever I get a chance to attack this project. As it is, I think my suspension and hydraulic jack issues need to take priority since my AC units will keep the MH at a comfortable temperature.
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Old 07-31-2018, 05:04 AM   #9
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Quote:
Originally Posted by Camper_bob View Post
I'll say that's on-topic overall.

No, I have not. Most of the major sources of heat I have, DW is not allowing me to do anything about. She DID allow me to put Reflectix in the skylight, and that made a pretty big difference. Other major sources of heat include basically all the windows, the cab, the door, etc. DW does not want me to put Reflectix in those openings because she thinks it looks "trashy". I do have quite a lot of tint left over from when we tinted the windows in our S&B house, and I intend to use that in the MH. The windows are already tinted, but this extra layer should block out more UV and heat. Most of the time we also put a "mask" over the cab of the MH, and that helps as well. If we do that, in addition to bulking up the "curtain" that divides the cab and the chassis, I'm betting we can block A LOT of heat.

Slide toppers are also on the short-list of mods, and that should help with the load from the tops of the slideouts, even though those are somewhat insulated with overhead cabinets.

Anyway, I'm also discovering I may have some heat sources under my bed as well. So next time I have it in the driveway (should be week after next) I will take an exploratory walk around with my temp gun and see what I can see.

Like I said, the rig DOES cool off, and the units WILL cycle, it just doesn't seem to be as efficient as it should be?
Bob, when you get a chance look at my post on the 2016 Greyhawk bed platform. Iíve done a mod under there after taking heat readings. The electric box would get up to about 156 degrees before the fan would kick in to cool it down so I installed some vents. Iím also in the process of rebuilding the mattress platform. Iím taking pictures and will post when itís completed. Our new mattress is 10Ē thick and Iím making an insulated platform. Iíll post when finished. Jimmyd
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Old 07-31-2018, 05:23 AM   #10
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Onr suggestion if you have a ducted system is to minimize the output air that comes out of the roof units. The output and intake are so close together that there is no way a lot of the output is pulled right back into the return. No matter how well they are seperated.

Getting the supply air down the duct work and farther away from the return has to help the units efficiency.

I think measuring it with the IR thermometer that way would be more accurate.
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