RTU tripping breaker and Super boost

[smertz]

A month ago I was called to look at an RTU (carrier MN48TJD007521) that was intermittantly tripping the circuit breaker. Unit had a bad condensor fan, which I presumed led to the melted wires on the compressor terminals. I replaced compressor fan, melted wires, and installed a terminal rebuild kit on the compressor terminals. Unit seemed to run fine. This week manager calls me back up and kindly explains that the unit has tripped the breaker again. I go back, and look unit over, tighten all electrical connections and start unit up again. It runs fine but I have lost confidence in it.

Pressures are 80 and 370 psi with 13 degree sh and 36 degree subcooling (piston metering) Identical unit sitting on roof next to it has same pressures and runs with no problems. Air off condensor is 132 degrees with 97 degree outdoor ambient.

Would a super boost capacitor help this 3 phase unit. I have one (SPP8E)that i ordered for this, but when I recieved it, carton says it is good for single phase, will it work since it is only using one phase for the start winding?

Amps are 23, 24, 23 again identical to unit next to it.

[Senior Tech]

Head pressure is high...way high on both units, find out why and you may solve the problem with out the super boost.
Sub-cooling is also high...sounds like overcharge.

[smertz]

My first thought was that the unit was overcharged as well. Hi subcooling and head pressure, however it is right on with the manufacturer's charging chart for this unit which related outdoor db, suction pressure, and sh. Could taking some refrigerant out lower head pressure without throwing the charging chart variables out of balance?

Thanks for the reply.

[freonrick]

you dont use any capacitors on 3 phase at all. unless it is a power factor capacitor. if amps is ok then look at connections at breaker or weak breaker. breaker tripps by heat. it doesnt care if the heat is caused by high amps or loose connections. i would wash the condenser coil. if it is double row then split it and clean.

[Senior Tech]

Originally posted by freonrick
you dont use any capacitors on 3 phase at all. unless it is a power factor capacitor. if amps is ok then look at connections at breaker or weak breaker. breaker tripps by heat. it doesnt care if the heat is caused by high amps or loose connections. i would wash the condenser coil. if it is double row then split it and clean.
My bag...your are correct, I hate it when I make a mistake...with a witness...no, I uh, was uh, testing you, yah thats it, this was a test and congratulations you passed!

[Senior Tech]

As FreonRick so graciously reminded us, you need to make sure the condenser coil is clean, all the way thru, also make sure your condenser fans are turning the right direction, etc...once you have checked all this come back and keep us posted as to the results. (I routinely find units overcharged to compensate for other problems...trick is to find the other problem)

[cynic]

anyone want to bet the condensor coil looks like this or worse ? :)

http://webpages.charter.net/conflused/workpics/spcond.jpg

[absrbrtek]

Im with youy on this one. 370# of head, no way is the condenser clean.
Originally posted by cynic
anyone want to bet the condensor coil looks like this or worse ? :)





[Edited by absrbrtek on 07-11-2004 at 12:10 PM]

[hsc tech 1]

Hey Cynic, thats looks like Trane.

[sonc]

If the liquid line is as hot as the discharge line, Better clean the coil lol

[smertz]

Dirty condensor, yes, makes perfect sense. Wish I had remembered that at the get go. Hot sun must have fried some brain cell. I will clean and let you know the pressure drop.

Thanks

[smertz]

Condensor clean, fins straintened , pressures are 75 and 280. Outdoor Ambient is 90. I was thinking a little lower head pressure still? Amps dropped from 23 to 21. Thanks for the ideas.

[sonc]

280 head at 90 degs?.. stick a fork in it, man
that job is done.

[psycho-metric]

Ive got several 48tj's under contract. The overload "breaker" is sized pretty tight on full load. Ive always found the problem to be a dirty coil. You shouldn't have any more problems.

[chs]

thoughts on charging...1. fixed metering device look at superheat. TXV look at subcooling. Package units you can weigh a charge.

[R12rules]

Originally posted by chs
thoughts on charging...1. fixed metering device look at superheat. TXV look at subcooling. Package units you can weigh a charge.

I liked this one.



One more thing. When I get a triped breaker, I look for hi meg ohm on the compressor.

[service guy]

You Know sometimes I wonder about these carrier Engineers I once found a 20 amp breaker (breaker factory installed) on a Evap motor Rated for 19.0 FLA ??????? gee wonder what happens when the fan starts???