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Old 08-24-2019, 05:18 PM   #1
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How to properly check/charge rooftop ac?

Coleman 13,500 rooftop ac circa 1999. Getting 10 degree temperature differential between intake and exhaust. Pulls about 7 amps at 95 degree ambient temperature. Evaporator and condenser are both clean. Iíve read that these ac are charged to an amp draw at a certain temperature and not a low side/high side pressure range like automotive acís. Before I chunk this ac in the trash I would like to confirm that itís low (too low current draw?) and if so, possibly install one of those piercing ports on the low side and add a smidge of R22. Looking at this data plate, would the amp draw be the
Fan Motor FLA of 2.9 plus the
Compressor BCSC of 8.7 which would equal 11.6?

Or would it be the RLA of 7.6 plus the fan FLA of 2.9 equaling 10.5?

Or neither.

If so, at what temperature is that at? 90? And is it 1 amp change per 10 degrees of temperature rise/fall?

Thanks.
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Old 08-24-2019, 05:25 PM   #2
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too much mumbo jumbo..its old an worn out.. change it out. R22 is hard to find and would cost a fortune to put a Shrader valve on it and charge the unit.. It probably has a leak in the evaporator and not worth fixing.
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Old 08-24-2019, 05:40 PM   #3
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Originally Posted by tanman32225 View Post
too much mumbo jumbo..its old an worn out.. change it out. R22 is hard to find and would cost a fortune to put a Shrader valve on it and charge the unit.. It probably has a leak in the evaporator and not worth fixing.
Thank you for your insightful information.
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Old 08-24-2019, 05:59 PM   #4
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Quite possibly the compressor is worn out or you have a leak. You would have to install ports on the hi & low pressure sides to properly test it. Your looking at a few hundred just to find out what the problem is , then there is the cost to repair it, and you still have an old unit.
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Old 08-24-2019, 06:28 PM   #5
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20 years out of a rooftop AC unit is darn good. This puppy doesn't owe you anything and should be laid to rest. The gentlemen above hit this nail on its head. Easy for us to say "Go buy a new one" with your wallet but any money put into your unit will be money lost.
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Old 08-24-2019, 06:35 PM   #6
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LRA-----Locked Rotor Amps (max current to the motor when it is in a locked)

RLA-----Rated Load Amps (calculate the max overcurrent protection permitted)

FLA-----Full Load Amps ( motor's rated-current at rated-load and rated-voltage)


BCSC---Branch-Circuit Selection Current (determines ratings of motor branch-circuit conductors--always higher or at least equal to RLA)


Compressor RLA PLUS Fan Motor FLA-----7.6A +2.9A =====10.5A
Those figures give you an indication of how close unit is running to specs
BUT not good for figuring IF it is cooling properly


AS noted above.......
R22 plus shrader valve (which leak) plus time/labor IF you have the proper gauges might be 'fun experiment' but hardly worth it for that old of an RV a/c unit (20+ yrs old)
Got your monies worth !
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Old 08-24-2019, 07:05 PM   #7
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Originally Posted by Old-Biscuit View Post
LRA-----Locked Rotor Amps (max current to the motor when it is in a locked)

RLA-----Rated Load Amps (calculate the max overcurrent protection permitted)

FLA-----Full Load Amps ( motor's rated-current at rated-load and rated-voltage)


BCSC---Branch-Circuit Selection Current (determines ratings of motor branch-circuit conductors--always higher or at least equal to RLA)


Compressor RLA PLUS Fan Motor FLA-----7.6A +2.9A =====10.5A
Those figures give you an indication of how close unit is running to specs
BUT not good for figuring IF it is cooling properly


AS noted above.......
R22 plus shrader valve (which leak) plus time/labor IF you have the proper gauges might be 'fun experiment' but hardly worth it for that old of an RV a/c unit (20+ yrs old)
Got your monies worth !


Thank your for your information. I can check amperage for free, add a shrader valve for $8 and I already have the R22. Even if it doesnít work itís no big deal.
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Old 08-24-2019, 07:15 PM   #8
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First off the saddle clamp valve are prone to leaking. i do not use them except for a temporary fix. Next, the easiest way to check unit performance is to run the unit on high fan and check the temperature difference between inlet air and outlet air temperature. The outlet should be 20 degF (+/- 2 degF) lower than the inlet. Both readings should be taken as close to the unit as possible.

Use a real liquid filled or temperature sensor thermometer to get your readings. The infra red temp guns do not read actual air temperature/ They only read the temperature of the surrounding surface.

And a 20 year old A/C unit really is not worth repairing. And I charge by pressure reading at the compressor suction and discharge while watching amps. For the manufacturers, the charge is put in by weight.

Ken
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Old 08-24-2019, 08:36 PM   #9
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https://www.airxcel.com/docs/default...e.pdf?sfvrsn=5
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Old 08-24-2019, 09:15 PM   #10
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If you have the stuff and a set of gauges and have or learn the knowledge, go for it. Nothing lost in trying if the unit isn't putting out rated cold air.
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Old 09-08-2019, 06:59 PM   #11
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The previous thread indicates that our rooftop ac temperature differential was only 10 degrees and that the amp draw was below spec. According to the manufacture, at 100 degrees it is to be RLA + 1. Data tag states RLA should be 7.6 plus the 1 make 8.6. I was getting 6.6 amps.



I added a piercing tap the the low side line. Slowly added a few ounces of R22 and the amp draw increased to 8.6 and temperature differential increased to about 18-19 degrees. It seems to be working as designed. Hopefully the leak is really, really slow. Ha
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Old 09-09-2019, 06:17 AM   #12
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I added a piercing tap the the low side line. Slowly added a few ounces of R22 and the amp draw increased to 8.6 and temperature differential increased to about 18-19 degrees. It seems to be working as designed. Hopefully the leak is really, really slow. Ha
I always think it's funny that a do-it-yourself forum consistently condemns the A/C unit based on age. I've charged many including one currently on my roof and they all worked for years afterwards.

Good job!
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Old 09-09-2019, 11:59 AM   #13
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I have the same AC/s and because I have to modify everything, I added hi and low ports along with a TXV valve.



Hi side ran around 300 and the low side was 77. Compressor pulling 7.7 amps in 95 degrees.
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Old 09-09-2019, 05:45 PM   #14
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WOW! I wish I was brave enough to do something like this!
Watching...
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