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bad suction valves or undersized unit?

You will need the following information:

Assure matched components.

Make sure the airflow is at 400 CFM/Ton

ID the metering device, if fixed; make sure the tonnage matches the piston size.

If TXV, make sure the bulb is tight and insulated as required.

If TXV measure and record the suction temperature at the evaporator outlet.

If fixed measure and record the suction temperature at the condenser.

Measure and record the liquid temperature at the condenser outlet and inlet.

RA wet bulb and dry bulb measured at the air handler of furnace.

RA wet bulb and dry bulb in the conditioned space.

SA wet bulb and dry bulb measured about 24” downstream of the evaporator coil.

Measure and record outdoor air temperature.

Measure and record the condenser air discharge temperature
Measure suction and discharge pressures. Make sure you ZERO your gauges.

Measure compressor amps and compair to full load amps

Jim Bergmann


  • ddenny
    ddenny Member Posts: 75
    bad suction valves or undersized unit?

    got a call for not enough cooling in an office space inside a warehouse. the unit was doing some cooling and was pulling down to 82 degrees on one of our recent very hot days. my first impression was there was nothing wrong other than unit being undersized. but when I took the pressure readings I got 325 on high side and 110 on suction side on an r-22 system. the amp reading was 17 on the common wire of the compressor. the condensing unit is 3 ton. I'm getting condesation off the evaporator and on suction line, did'nt take suction line temperature reading though. question is wil I get that high a pressure reading if nothing is wrong other than it being undersized. don't want to change the compressor and get same results. thankyou.
  • Empire_2
    Empire_2 Member Posts: 2,343
    First off,...

    What is the Outside temps? Is the coil clean, In and out?? Accurator I presume.... Your head pressure is hi even for a 90-95* day. Temps would be nice so we can plot er'''' on a T/E chart.....;-)

    Mike T.
  • Empire_2
    Empire_2 Member Posts: 2,343
    Jim is correct in asking for the above...

    But first, give us the basic temps that will dictate what the system is or is not doing. Do you have a surface probe to measure line temps? The more info we have the better. Let's see if it's an easy problem first. I hate when tech's go on a JOB and dive into step 12 before they check out 1-12!!!!!!!!!!!!!!! No Diss. intended..;-)

    Mike T.
  • don_182
    don_182 Member Posts: 69
    I know

    all the system I've been out on this week are undersize.

    Ok let me rephase that...we are 12 to 15 degree with the heat index above design we have reduce in capacity.

    Your thoughts?

    They're all saying my house will not go below 84and my stat
    is on sixty.LOL.
  • Techman
    Techman Member Posts: 2,144
    Valves or Unit

    Evening! I think the unit is undersized because of the hi suction and a hi head,with bad reeds the suction would be hi and the head should be lower, without an over charge of freon..??
  • subcooler
    subcooler Member Posts: 140
    What kinda TD ?

    Good valves are indicated by the 3 to 1 compression across the compressor. 325 head and 110 suction. If this unit has a bullet type restictor for the metering device the unit is probably a little overcharged. If you had 210 head and 70 suction the compressor would still be good. 95% of compressor that are changed out are caused by the system design not the compressor itself.
  • ddenny
    ddenny Member Posts: 75
    bad valves or undersized unit

    thanks guys
    I,m going to take those measurments jim suggested on this unit if I can get back there. the tenants of the space called me but the owner of the bldg is getting his guy to look at it so I may not get back there. however I printed out your replys and next time I need some help I'll have the info for plotting the pe chart.
    I found out the condensing unit is a 3 ton and the air handler is an old rheem cap tube 5 ton rectangular shaped evaporator. that mismatch may be my only problem. it's not a single cap tube. the liquid line goes into a manifold and multiple cap tubes branch out to different parts of the evaporator.
    is there a god rule of thumb for load sizing? like one ton per 400 square feet? the conditioned space is in side a warehouse that is not airconditioned. the only seperation between the warehouse and the airconditioned offices are sheetrocked walls and ceiling tiles. no insullation above the ceiling tiles or in the walls.
    I'm looking for an "electronic thermometer" so I don't have to use my 25 ft. tape measurer in a busy office area . thanks again for your help.
    dennis carroll
  • Empire_2
    Empire_2 Member Posts: 2,343

    5 ton evap with 3 ton condenser..No wonder it is not running correctly. I'll bet that the unit is overcharged cause nobody bothered to see if the evap and cond matched.

    My .02

    Mike T
  • Techman
    Techman Member Posts: 2,144

    Hi Mike T !Would the 5/3 system work as a big dehumidifier?
  • Empire_2
    Empire_2 Member Posts: 2,343

    I might. The current S/H will be sky hi.;-) I'll bet he's only effectively using 1/2 to 2/3 of that coil if that...

    Mike T.
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