Rooftop AC Discharge Temp

[oldjohnt]

Anyone know what temperature the "cold" air being discharged out of a 2006 Duo Therm by Dometic "Brisk Air" non ducted AC should be ??? Mine doesnt "seem" cold enough so I placed a thermometer direct in front of it, yet (Yes the compressor is engaged and running full time) after 30 minutes its still around 61 degrees which I "think" isn't cold enough. NOTE this isn't any exact or perfect or scientific test, simply a thermometer one inch out of the discharge direct in its air flow, but of course the RV interior ambient conditions still cause an influence I'm sure. If I recall in automotive AC systems they discharge air in the 40+ degree range.

Thanks in advance

John T

[Ranger Smith]

I believe the difference is 20 degrees cooler than ambient outside temp. That is what I have been told but Im not an expert in AC. The 20 degrees is the difference between the supply and return. Not outside temp. My error. 

[Ronbo]

61 is great, unless it is 50 outside. Ranger is correct, 20degree difference is what is expected although I have always gotten more.

[D&J]

You should get a 15 to 20 degree drop across the evaporator, put a thermometer at the return and one at the discharge. If you are getting 60' at the discharge and 80' at the return it's working like it should and will just take time to cool the unit down.

Denny 

[oldjohnt]

THANKS GANG, Wellllllllllll its 90 outside and if my discharge air is 60 MAYBE IF IT AINT BROKE I WONT FIX IT !!!!

  John T

 

[Kirk W]

2 hours ago, oldjohnt said:

Anyone know what temperature the "cold" air being discharged out of a 2006 Duo Therm by Dometic "Brisk Air" non ducted AC should be ?

There is no designed discharge temperature as that is determined by the air supply temperature. Dometic service states that the ΔT (or differential temperature) as between 18 & 22°. To determine this you need to first measure the air temperature into the cooling coils, followed by measuring the air temperature out and subtract. Most a/c techs recommend using a good dial thermometer to do the measurement. 

If yours is greater than 22° there is a high probability of freeze up problems.

[TXiceman]

Also, do the temperature check with the fan on high, never on low.  DO NOT use and Infrared temp gun as it will not measure air temperature.  It only measures the temperature of a surface.

Ken

[hemsteadc]

My discharge is around 55° always. If it were just 20 below ambient it would take forever to cool the coach.

[oldjohnt]

4 hours ago, hemsteadc said:

My discharge is around 55° always. If it were just 20 below ambient it would take forever to cool the coach.

 I tested mine a long time yesterday and 61.2 was the lowest it ever got, 55 (if physically and mechanically possible)  would be better..............

Again THANKS to all

John T

[Bill w/bus]

Its all about dT, delta temperature.  A properly working unit is defined as a dT of 15-23 degrees F with fan on highest speed. 

 

Bill

[Kirk W]

On 6/19/2018 at 6:07 AM, oldjohnt said:

 I tested mine a long time yesterday and 61.2 was the lowest it ever got, 55 (if physically and mechanically possible)  would be better..............

Have you considered the possibility that your cooling coils (evaporator) may need to be cleaned? None of us mentioned it but as the coils become coated with dirt the efficiency of them will decrease and over time it can dramatically lower the ability of the a/c to cool the inside air. That same thing is true for the condenser coils if they should become plugged with foreign materials such as cottonwood seeds or most anything else. The inside tends to get bad first due to it normally being damp to wet, but outside can also be plugged with flying debris. 

[oldjohnt]

Yep, I considered all that and both coils are clean n free.

Thanks

John T

[Clay L]

One thing to note: Since most/all ( all that I have seen) RV ACs do not draw air from the outside but instead recirculate the inside air, the 20 to 25 degree difference is between air  being drawn into  the AC and the air coming out. 

[oldjohnt]

UPDATE   SUCCESS

 Welllllllllllll I bought a new rooftop AC. Sure, its the Delta T that matters, BUT THAT BEING SAID on a day with about the same outdoor temperature and humidity, and recall my old AC air discharge temp was 61.2 Degrees, the new AC discharges air at 53.7 Degrees YAYYYYYYYYYYYYY IM a Happy Camper !!!!!!!!!!!!!!!!

Thanks to all who responded

 

John T

[hemsteadc]

23 hours ago, oldjohnt said:

the new AC discharges air at 53.7 Degrees 

That sounds right.  Excellent.

[Kirk W]

If all you measure is the output temperature, that will be determined by the thermostat setting, once the inside temperature has stabilized. If you measure the discharge temperature soon after you start the a/c and the inside is still hot, you may be disappointed by what you read. It is just basic thermal dynamic principles in action. 

[nwtraveler]

If you feel like you're not getting cooled down, check the divider in the

plenum area, by removing the inside cover. If it is not securely in place

you A/C could be just recycling the cold air between the intake and output

instead of directing it out through your ducting. 

[oldjohnt]

Sooooooooooooooooo glad I got it fixed, its been in the nineties last couple days and UNLIKE the old unit, the new one is keeping the RV cool (regardless of reasons), pumping out MUCH COLDER air with tons of condensation running off the roof, so I'm still a COOL n happy camper. Problem solved.

Thanks again

 John T