AC outlet temp

Keystoned · 05-02-2020, 03:48 PM

My unit has a Mach 15 and I'm wondering what the outlet temp should be with the fan on high. Just got a 30A outlet wired up for the 5W and running it for the first time since we got it in January. I want to verify it is operating correctly.

**chuckster57** · 05-02-2020, 04:52 PM

A 15-20 degree drop from ambient is the norm.

Keystoned · 05-03-2020, 06:23 AM

Is that at the outlet of the AC or the interior of the of the trailer? For car and truck ACs, performance is measured at the AC vent...

**chuckster57** · 05-03-2020, 06:34 AM

We measure at the AC grill. Those units with the "whisper quiet" require a different approach.

**JRTJH** · 05-03-2020, 06:50 AM

The way that I check it (not that it's the only way or even "the factory way") is to turn the A/C on, let it stabilize for about 1-2 minutes, measure the temperature of the air flowing into the air return (filter opening) and measure the air temperature flowing out of the outlets. I try to find an outlet that's about "half the distance of the furthest ceiling outlet"...

The "ambient air" is the air flowing into the filtered return air inlet and the "chilled air" is the air flowing through the ducting system, to the ceiling vents. It usually occurs, that the further you go from the A/C unit, through the "hot ducts that are being heated by sunlight on the roof" the warmer the chilled air will become. That's why I try to find a ceiling vent about "halfway between the unit and the end of the run"....

Normal difference in temps is around 15-20F. As the interior of the trailer cools down, the temperature of the air flowing into the A/C will cool and so will the temp of the air flowing out of the vents... It "should" maintain around that 15-20F differential.

Keystoned · 05-03-2020, 07:54 AM

Well guys, here is what I measured yesterday. Turned on AC at mid day after 30A install and ran a few hours before recording the following.
Outside temp = 90F with full sun
Inside temp = 82F, remote sensor on the kitchen island
AC outlet temp = 52F, main sensor in airstream for several minutes as the sensor only updates about once a minute.

Mine is not whisper quiet at all, lol
Pretty sure the 5W was heat soaked and starting earlier would show lower inside temps. The dark brown front cap does not help at all, nor the tannish color of the roof and siding.

**chuckster57** · 05-03-2020, 07:56 AM

Looks to me like your AC is doing its job.

**flybouy** · 05-03-2020, 07:58 AM

The change in temp is referred to as "across the coil" so technically the measurement should be on either side of the coil to eliminate induction heating (and cooling) of the air ducting. The reasoning is that the design, and construction of the air ducting can vary widely and greatly influence the measurements.

If your unit was poorly constructed (that never happens right?) then the distribution could be leaking a vast amount of air into the space between the ceiling and the roof. The result could be a perfectly functioning ac unit that doesn't cool properly. If you can't get to the coil my suggestion would be to take a temp reading at several or all in most RV's at the outlets and take the average of that number. If the delta T is too shallow (below 15 deg but not greatly below then it probably warrants checking at the coil. On most units it's just a matter od removing the return air grill to access it.

travelin texans · 05-03-2020, 10:50 AM

Quote:

Originally Posted by Keystoned

Well guys, here is what I measured yesterday. Turned on AC at mid day after 30A install and ran a few hours before recording the following.
Outside temp = 90F with full sun
Inside temp = 82F, remote sensor on the kitchen island
AC outlet temp = 52F, main sensor in airstream for several minutes as the sensor only updates about once a minute.

Mine is not whisper quiet at all, lol
Pretty sure the 5W was heat soaked and starting earlier would show lower inside temps. The dark brown front cap does not help at all, nor the tannish color of the roof and siding.

If you have a way to inspect inside the front cap you'd most find a layer of reflex type foil & if there's any insulation it's probably vibrated down into a pile with nothing on the top portion.
Mine had a shoe shelve in the front & the above is what I found in mine. I stuffed as much insulation as possible in both sides of the shelve & sprayed adhesive behind the shelve to front cap to hold up what thickness I could there. Made a huge difference in the bedroom temperatures.

xrated · 05-03-2020, 01:07 PM

Quote:

Originally Posted by JRTJH

The way that I check it (not that it's the only way or even "the factory way") is to turn the A/C on, let it stabilize for about 1-2 minutes, measure the temperature of the air flowing into the air return (filter opening) and measure the air temperature flowing out of the outlets. I try to find an outlet that's about "half the distance of the furthest ceiling outlet"...

The "ambient air" is the air flowing into the filtered return air inlet and the "chilled air" is the air flowing through the ducting system, to the ceiling vents. It usually occurs, that the further you go from the A/C unit, through the "hot ducts that are being heated by sunlight on the roof" the warmer the chilled air will become. That's why I try to find a ceiling vent about "halfway between the unit and the end of the run"....

Normal difference in temps is around 15-20F. As the interior of the trailer cools down, the temperature of the air flowing into the A/C will cool and so will the temp of the air flowing out of the vents... It "should" maintain around that 15-20F differential.

John, you exactly nailed it with that answer.

xrated · 05-03-2020, 01:09 PM

Quote:

Originally Posted by flybouy

The change in temp is referred to as "across the coil" so technically the measurement should be on either side of the coil to eliminate induction heating (and cooling) of the air ducting. The reasoning is that the design, and construction of the air ducting can vary widely and greatly influence the measurements.

If your unit was poorly constructed (that never happens right?) then the distribution could be leaking a vast amount of air into the space between the ceiling and the roof. The result could be a perfectly functioning ac unit that doesn't cool properly. If you can't get to the coil my suggestion would be to take a temp reading at several or all in most RV's at the outlets and take the average of that number. If the delta T is too shallow (below 15 deg but not greatly below then it probably warrants checking at the coil. On most units it's just a matter od removing the return air grill to access it.

Actually, most folks call it differential temperature.....the air entering the evaporator intake vs. the outlet air from the evaporator. Either way though, the thought is the same.

Keystoned · 05-03-2020, 01:17 PM

Thanks for all the tips that I will keep in mind for a future adventure or two.

ajlight · 05-03-2020, 04:37 PM

I would defiantly check the duct after the last vent each direction and at every vent. Most every trailer we have had needed work.

Keystoned · 05-04-2020, 05:00 AM

Good news everyone...ran it yesterday beginning at 75F and same conditions later. It went up to 77 but the bedroom area was warmer. While shutting it down I closed another vent slide at the unit and a bunch more flow was felt from the bedroom vent, so there is hope.
Outside temp = 90F with full sun
Inside temp = 77F, remote sensor on the kitchen island
AC outlet temp = 52F assumed, not measured today

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