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good candidate for a p/e chart evaluation?

I just wrote a letter to the wall but lost it in cyberspace so here goes the same letter again.
have a problem with two 5 ton rheem condensing units at a strip mall in a hair salon. they can run for hours or days but eventually I keep getting call backs for tripped breakers especially on one of them. the electical panel is a 3 phase 208. it's not one of those wye panels that has a high leg to ground. every leg ground is the same.
the panel is 3 phase but the condensing units are single phase 208 / 230 volt. the breakers are 40 amps and most of the time are running about 0ne amp higher than full load amps. however I have seen both of them creep up to 40 amps plus. the circuit breakers are warm to the touch especially when the amperage is high. the supply voltage is a little low but not enough to make a difference I think. about 202 or 204 but I've seen it drop to 194 or 196 volts. I pulled both breakers out to inspect the back but found no sign of burning. changed them anyway to no avail
here are some measurements I took on the unit that trips the most.
air into condenser 85
air leaving condenser 123 (seems high but the condenser doesn'nt look dirty)
suction pressure 76#
suction line temperature 52
head pressure 285#
liquid line temperature 98
return air into evap 73
supply air to conditioned area ......I forgot to write it down but remember it was low I think 47.
I took professor silberstein's class but am only halfway reading through the material so I don't know how to plot a p/e chart.
I don't have a wet bulb thermometer or a way of checking the airflow. would appreciate your help thankyou
dennis carroll


  • Charles G.
    Charles G. Member Posts: 113
    Voltage drop

    Yes, you're voltage drop IS enough to make a difference. Allowance is +/-10%. You're already seeing 40+ amps--system should run @ 80% of breaker rating. Check wire size and max. allowable breaker size for units. Beauty shop and hot weather--guaranteed voltage problems esp in older shop/building.
    You may also consider a time delay-on-break relay. If the unit(s) drop out, they won't try to come back on too soon. But you need to address the electric problem...
  • Empire_2
    Empire_2 Member Posts: 2,343
    Power problem

    Also don't forget that the hair salon has most of it's gadgets running at all times of the day. I have seen problems with service to buildings, but the Electric company in your area can verify this. We also have to take onto consideration the TOTAL load on the panel when everything is running......

    A line monitoring device called "Line Backer" can be used to accurately tell you what tripped the breaker. Very expensive, but worth the price. Leave it on the system if you purchase it.

    Mike T.
  • Techman
    Techman Member Posts: 2,144
    Voltage Drop!

    Evening. A voltage drop equals an amperage increase with inductive loads - compressors and fan motors.Hows your low voltage? 19-15v will chatter any contactor, tripping the breaker.
  • RadPro
    RadPro Member Posts: 90
    Dirty condenser


    You should wash out that condenser even if it looks clean! I was told once that the only clean condenser is the one you just washed out yourself!! You might look "foolish" once in a while, but most of the time you will be vindicated when the black and brown water flows and the crud starts pouring out from the fins.

    From your readings you have too much subcooling! Is it txv or fixed orfice? Check the charge also.

    Don in Mo
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