coleman Mach - Temperature Differential model 8333e856

[jodeb720]

Afternoon all,

As I sit here in the campground, sweating (as it's in the mid 90's), My trailer AC unit doesn't seem to be keeping up with the expected cooling temperature delta.

I've been told (or read maybe onhere) that the delta between intake and exhaust should be 40 degrees.

I removed the cover for the intake (it's both ceiling vented and has vents that open on the output side, held my thermometer in the air blowing down and it was about 62 degrees. I then put the thermometer down on the counter while I resealed all the cracks and crevasses with aluminum tape - I figure every little bit helps, right?

Anyway, the temperature in the trailer is 82 degrees.

I checked the air filter - and I cleaned it the last time I was out - and yes, it's still clean.

I expected a temp delta of 40 degrees and I'm only seeing 20.
Model 8333e856
Coleman Mach

I'm assuming it's a 13,500 btu unit -

So - my questions:
1. Is a 20 degree delta acceptable or am I expecting too much?
2. Am I missing anything?


Thanks in advance!
Josh

[j-d]

I quickly read this thread and if a couple items were addressed, I missed them:

1. How OLD is this system and have the COILS, particularly the Evaporator Coil, at the front of the unit, under a sheet metal shroud, been Cleaned?

2. It's ducted, so is the ducting OK? I don't have a ducted, but I understand there can be problems right at the unit where flow is reduced.

3. On the roof, is there baffling (foam blocks) along the vertical edges of the Condenser Coil, so air being exhausted out the sides, isn't being sucked around the corners of the Condenser?

Remember, a 20* "Split" doesn't mean the coach won't get below 80* if it's 100* outside. Once it cools the interior to 95* then split means the cool air can now be 75*. If it cools the interior to 80* then you could (at least theoretically) drive it down into the 60's. But, as mentioned, if the A/C lacks the capacity to bring interior temperature down at all, then this can't happen.

[CJW8]

There is a guy on here that claims 40 delta T. The only way that is possible is because he is getting recirculation but he doesn't believe it.

[jodeb720]

After returning and talking to my BIL's (both of them went with me) neither of them had issues cooling their TT's. One had the dump out of the AC unit (but in a 20' trailer) and the other has a 27' with ducted venting.

I'm thinking the Jdubya is correct. If I open the grates on the output of the AC unit - it'll put 90% of the cooling in an area - but not in the bedroom; However, if I think about the size of the ducts - I'm guessing that it's unable to move the air through the AC unit effectively to reduce the air temp.

As to the 40 degree delta, I'm not sure where I got it - but I thought I read it on here.

Ironically, the input temp on the AC unit was about 85 degrees, the output temp in the duct was 55 degrees - but I suspect it's a volume issue - moving enough of the air through the AC unit to remove the heat effectively.

I had the blinds drawn and the vents closed - but didn't have foam in the vents or the shower skylight.

Thanks!

josh

[CA_Traveler]

Have you covered the windows, roof vents, etc to help lower the temperature?

[jdubya]

I agree with dougrainer that you need a larger A/C unit, he is also right about the differential. But I am pretty sure that you don't believe that the A/C unit was designed to run slow air speed, rather that something is causing slow air speed. That something should be causing the evaporator to freeze up. I have never seen a Coleman A/C freeze up when the ducts run slow - the ducts air will run slowly because they are trying to push a large amount of air through a small hole into the large duct to quiet things down. The air passing over the evaporator coils will be just as great either way. To prove it, measure the size of the hole that the air goes through to enter the duct work - I expect it is something like 4" X 6" and then the ducts are 3" x 10" that means the air passing through the 24 sq in will speed up to get to the larger volume 30 sq in x 20 ft or more. And those ducts are both directions so they are times two compared to that little hole the air is forced to enter the fan through.

[dougrainer]

1. Your model is a 13.5 btu
2. IF you have a slide out and you are at 25 foot, the 13.5 will be marginal to cool that RV in hot temps above 90 degrees. Even if ducted
3. Curious, WHERE did you get the idea that the Delta was 40 degrees?????? It has always been 18 to 23 degrees.
4. "If the air moves across the coils, slower, it'll cool more than if the air moves faster. I can't believe they designed the evaporator to move the air across it slower though. That makes no sense."
The slower the air moves thru the evaporator the MORE cold the air can absorb. That is why running on LO COOL can cause a freeze up. The air moves slow and does not remove the acumillated cold on the Evaporator. Your model has just 1 fan motor and has 2 selections for Fan--HI and LOW.
5. The simple answer is your AC is not large enough to do the job. You need a 15k. Doug

[pnichols]

I suspect that the differential of your A/C is not the problem.

More likely, it's the BTU capacity of your A/C that's the problem - versus the size of your RV's interior volume versus how well insulated the RV is versus how hot the outside temperature is.

[ScottG]

Nothing short of a commercial chiller is going to do 40 degrees differential.
Twenty is great but you need more capacity. Time for another AC unit.

Doesn't your ceiling unit have a dump feature? LIke a grate you open so all the air comes out the bottom and not through the ducting?

[jodeb720]

Just a quick footnote.

The temp of the air coming out of the ducts is about 50 degrees - which makes sense if there is a lot of back pressure from the fan pushing the air out of the ducts.

If the air moves across the coils, slower, it'll cool more than if the air moves faster. I can't believe they designed the evaporator to move the air across it slower though. That makes no sense.

of course the follow up question is this:

If there is that much resistance in the ceiling vents, should it be that way?

Just a thought.

again, thanks!

josh

[jodeb720]

I always thought 40 degrees is the delta for AC Units...

Oh well. It's not keeping up with the heat here. I think it's the ceiling ducts are full of restrictions and the volume of air coming out is relatively low - and yes, I have the manual controls for air flow on the output closed up tight.

That fan puts out tons of air, but I think the ducting in the ceiling is too restrictive and it's not allowing a good flow of air.

Thanks everybody!

Josh

[the2sharps]

The Coleman-Mach website says "output temperature range of 16-22 degrees lower than the temperature taken in at the filter."

[Chris_Bryant]

20 is fine- better than most.

[newman_fulltime]

most ac units will only get a 15 degree diff from intake to outake