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Thread: discharge temp

  1. #1
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    discharge temp



    After a compressor change on a R22 system what sort of discharge temp can I expect, measured directly on the pipe at present it,s over 100C with the pressure at 210 psi, the pipe from the condenser is at 40C with the low side pulling to almost zero, I know this indicates low charge and I am in the process of charging this system but as far as I can work out the HS should be 200psi with the LS at 60 psi, I am recharging with gas that was previously removed there is about 10 Kilo still to go in and topping up with reclaimed R22,
    the previous compressor lost it's oil and seized, leaks etc have all been cured and tested to 250 pis any help will be great
    DM



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    Re: discharge temp

    what system is it? did u change the drier,does the pressure equalise when u isolate the condenser?u say youve repaired leaks,what did u vac to and any backdrop?condenser coil clear?-normally 58-60 and 240 on a basic ye olde air con

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    Re: discharge temp

    High suction superheat due to a low charge will cause a high discharge superheat once the suction gas has been through the compressor, what goes in comes out. Same as if there is liquid in the suction theres not much heat in the discharge.

    Jon
    Mostly found in Oxfordshire, UK :)

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    Re: discharge temp

    with 200psi head and almost zero on the low side surely indicates a restriction or blockage,or choked condenser!

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    Re: discharge temp

    This a Airedale condenser and dx unit the guy from Airedale came out and reckons it is all ok just needs gas and oil he did comment that the suction line was way to big in diameter cant remember what the size was 2 5/8 I think any way it was bigger than my pipe gauge would go round, coils have been steam cleaned, and with a K probe on the discharge at its outlet from the compresso I read 100c liquid line is 46c on both guages I have 110 psig on strat uup the high side will stop at 220psig and the low side eventually cuts out, however if I slowly keep the gas going in and the gauge around 50 psi it will run longer but it will still stop, I have new L/S & H/S pressure switches to fit but they sent two wire switches and the originals have three ?? I do not think I have a restriction as the suction line is getting very cold, the other thing is the sight glass is not within veiwing distance so I cant see what the hells going on
    DM

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    Re: discharge temp

    so at 46deg ur liq line should be warm!can u increase the flow through the expansion valve?

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    Re: discharge temp

    Yes it's warm ok bordering on hot I would do but again it;s three storeys up in an attic if I could just get SC with target and the dammned thing to run long enough for me to get to the dx unit I could start on the SH, But keep the input coming
    Devlin

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    Re: discharge temp

    looks like u need a wingman,someone to tweek valve whilst u moniter gauges and temps at the condenser-any oil traps on the system?

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    Re: discharge temp

    have u checked the td accross the filter drier?

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    Re: discharge temp

    High suction super heat equals high discharge temps., all the comp manufacturers say 15"c or below.. discharge pipe temp should be well below 100'C . So the oil temp will be also high and disappears into system probable cause of initial comp failure. Clean condenser and then check evaporator superheat, could be something simple as a stuffed TXV. Does compressor have head and oil cooler fan fitted. Aim for +35'C/ 13.5 bar g on R22 condensing, with sub cooling liquid leaving condenser in range of +28 > 30 'C.

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    Re: discharge temp

    Hi all and ta I have'vt checked the td at the filter, good point.
    there is no trap a fact that suprised the Airedale Tech
    No fans other than condenser fans which seem a bit slow I might have look in side the fan speed comtroller box
    Maggo can you explain a bit more your figures as I understand it is it HS 13.5 bg, with subcooled liquid at 28 bg
    Maguire

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    Re: discharge temp

    test the fan speed controller by open circiut of the sensor for minimum (tick over)speed for low ambients,and short the sensor for full speed-to proove the fans arent siezing.lower the set temp adjustable pot,check the sensor is correctly mounted,and u need to check the resistance of the sensor isnt cooked.

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    Re: discharge temp

    Cheers for that (your up early kids is it) I am going to the unit today to get all the info of the plate I am going to phone Airedale to get as mich spec as possible for this and, I will give the fan speed cont a try,
    Dev

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    Re: discharge temp

    I would expect the saturated condensing temperature (SCT) to be about 15-20K above the ambient temp. On a 20C day, the SCT should be about 35-40C, which corresponds to about 182-210psi. On a 25C day. the SCT should be about 40-45C, or about 210-235psi. Your pressures may not be high at all.

    It takes extra subcooling to push liquid up three stories... and you don't have any subcooling at all. Keep charging until the subcooling is about 8.5K... and you may need to take it even higher.

  15. #15
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    Re: discharge temp

    Thanks guys and you may well be right Gary today was a tad on the cold side with 8c outside air temp sct dropped a lot with a pressure hovering under 200psi definatly needs more gas however it now has an elctrical fault with the controlls off in the ahu, soelnoid closed, compressor will start with main islator on, the staff have been told to switch off at the ahu this results in the comp switching off on high side control all bloody day long hence the comp failure this and a oil leak some twat has re-wired this at some point to bypass a relay, now all I need is wiring schematic I hope Airedale will come through
    Thanks a lot guys you all have helped me out big time Devlin

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    Re: discharge temp

    The oil problems may also be due to the height of the evaporator above the condensing unit. On the off cycle, refrigerant migrates to the coldest spot which is usually the evaporator. The evaporator fills with liquid which then falls down the suction pipe to the compressor inlet, flooding the compressor on startup and flushing out the oil. The best solution is pumpdown with a solenoid at the TEV inlet. Next best would be to simply close that solenoid when the compressor is off.

  17. #17
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    Re: discharge temp

    Getting somewhere at last, , I had a look at SH today which was LS 20 psi gauge and 9c not understanding this I stopped the unit and had a look at the TEX 12 Yes I know, but as it happens it was screwed out less than a 1/4 turn so I closed it completly and took it out 2 1/2 turns, this has dropped the HS to 190 psi and the LS came up a bit, not much, but a improvement, However I still have concerns over discharge line temp @100c the gauges, reads 195 psi thats less than 40c condensing (from memory) I have left my notes in the car, any thoughts? never got back to check the SH as I had customers moaning because I had the heating off
    Devlin
    Last edited by devlin maguire; 24-05-2011 at 05:50 PM. Reason: updated info

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