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Old 05-28-2011, 02:32 PM   #1
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AC - How Cold Should It Blow?

AC question: How cold should the air be blowing out of the 13,500 btu unit on a 100 degree day?

Temp taken with infrared thermometer is around 43 degrees after washing off the coils....was 55 degrees prior to the wash off.

What should the temp be on a serviced unit?


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Old 05-28-2011, 03:27 PM   #2
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I have always been told an ac unit should be able to provide at least a 20 degree difference in temp.

Test cooling by placing a thermometer where the air is going into the filter, and one where the air is coming out. There should be at least a 20 degree difference with the compressor running.

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Old 05-28-2011, 03:47 PM   #3
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Agreed, the AC unit should lower the inside temp by at least 20 degrees from the outside temp...
In order to provide a 20 degree temp difference to the inside temp of the trailer, how cold would the AC have to blow?
Obviously, if the AC is blowing 80 degree air on a 100 degree day, the inside temp will never approach 80 it must blow cold?
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Old 05-28-2011, 04:10 PM   #4
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I found this by goggling the very question you asked. It is on a RV repair shop's web site:

A: The air coming out of the air conditioner will blow 18 to 20 degrees cooler that it draws in. If it is 90 degrees in your camper, it will blow out 70 degree air and will keep reducing the temperature as it sucks in cooler air.

The air temp blowing out of the air condition will be dependant on the inside air temperature of the camper, not the outside air temperature. The outside air temperature comes into play by raising the camper's inside temperature. You are absolutely correct that it may never reach a 20 degree difference between inside and outside. That will be dependent on the quality of insulation and other things such as humidity, etc.

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Old 05-28-2011, 07:06 PM   #5
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Had a auto AC tech tell me that temp at the output had to be less than 56deg and above 36 deg after about 15 min in 90 deg outside temp. All windows closed.

Based on that I would say your 43 deg sounds good but I have also read about the 20 deg difference between the IN and OUT air at the unit.
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Old 05-28-2011, 07:49 PM   #6
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The written specifications on both Dometic and RVP (Coleman) clearly state that a properly functioning RV air conditioning unit should display a 'delta T' (commonly known as the temperature differential between the cooled air measured at the duct or air outlet and the return air measured at the return air grill) should be 18*F-22*F.

This measurement is NOT dependent on the outside ambient air temperature. There are no absolute temperatures to measure. The 18*F to 22*F temperature differential is strictly related to the temperature of the air going into the evaporator and the cooled air coming out of the evaporator.

As you unit runs for any length of time, the inside temperature should be dropping as the air is cooling during this process, depending of course on your insulation factors, the outside ambient temperatures, the amount of solar heating the aluminum skin will receive from exposure to the sun and the size and capacity of your A/C unit.

Lew Farber...RVIA Certified Master Tech...ABYC Certified Master Marine Electrician
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