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plugged drier/expansion valve or stuck compressor valve or ???

Just grasping, Tim


  • archibald tuttle
    archibald tuttle Member Posts: 1,085
    plugged drier/expansion valve or stuck compressor valve or ???

    Frequent the heat side here regularly and thought I'd give Dr. Silberman a visit. Got this over at refrigeration-engineer.com also.

    Need Divine Intervention - plugged drier or expansion valve?

    It's not really all that bad having all the tenants glare at me while the mercury soars. I just wanted to have a catchy title and "Need Help "seems to be a little overused, with no disrespect to those who really need it.

    got an early 90s trane R-22 hydronic chiller (CGAC157HBN) two 7.5 ton circuits, drier/expansion valve design.

    One compressor blew at the close of last season. Had it on the list for replacement next week, but we got our first heat wave a week early (why didn't we do it in the off season you ask, too busy keeping the heat going) and no 'tween season. We were heating through Friday and on Saturday they want air-con, so no set-up for test running water through without shutting off the heating and shunting the water through the chiller. We could have picked a day and done it and then gone back to heat, but we usually count on having a couple down weeks. So much for the excuses.

    Anyhow, because of heat wave we decide to start the remaining circuit that was running fine last year. Unit is big enough that one circuit can just about handle the load anyway.

    Murphy strikes.

    Cleaned condensor. fill and bleed water circuit and insure flow through evaporator. Start unit, compressor kicks in fine, get brief, i.e. 5 second, flash of heat off high side right at the compressor and then nothing. Compressor running to beat band ultimately kicks off, I'm assuming one of the pressure actuated safeties after maybe a futile minute more of running. I didn't have any meters on it at the time and this is pre digital so I'm not getting any fault readouts, but the compressor is cool as a cucumber so I'm not betting on the thermal overload.

    I go for the gauges and get back an hour later and it is still showing 7 inches of vaccum on the return and almost a buck-50 on the high side.

    So, I'm assuming I have been graced with a plugged drier or expansion valve, but that doesn't make as much sense to me because it was working fine when we turned it off last fall.

    So after another couple of hours the vaccum in the return drops maybe halfway down to 3 or 4 inches and I brave a restart to see if I get any different information from actually running it. Vacuum pops right up over 10 inches on the suction but the high side needle doesn't even budge. Now I'm thinking maybe I got a stuck valve in the compressor or???

    This might be the most obvious symptom in the world, but I've never encountered it before and haven't managed to get Brian-UK to forward me (Brian-US) his troubleshooting guide so I'm going to the boards here, just like the Celtics later today, but I digress, for any thoughts on whats up or what else to test.

    Also printing the 300 plus page manual on compressor selection from the book section, but open to any recommendations for replacement of the bad compressor (and maybe the 'good' compressor as well). These are Trane "model H" hermetic 7.5 ton reciprocals as far as I know. The counter that I use is recommending scroll replacements as low as 5 ton since I have almost double capacity for the load (I didn't do the load calcs, but this is my emperical experience from running this unit and its predecessor for 35 years) and energy savings is more important consideration now than redundant capacity. (esp. unless somebody can point me to a better staging contoller and water temp management controller. On the heat side we use a TACO-PC 702 -- sorry don't have privileges to post a link to the specs for this control,it's a relabeled Tekmar proportional reset and two stage boiler controller -- but I have been unable to find an analogous device for cooling control)

    I assume that between the expansion valve adjustment and the fact that these would be undersized for the evaporator I wouldn't have a problem with liquid return and would get reasonable performance, but I concede immodestly here to being a whiz on the electric side while modestly to being just a straight OEM guy on the frig side to date.

    So I have no fear whatsoever of reworking the harness, for instance added thermal overloads for the condensor fans that drop out individual fans generally before a bad motor takes down the entire unit, but I have not had as much creativity in approaching the frig circuit.

    Given parts life, should I replace the expansion valves while changing the driers at this point or am I opening a can of worms. I have yet to remove the insulation to see how the capillary signal from the evaporator is installed. On the one hand, if I can test and confirm proper operation of these units in any way, it might be simpler to leave 'em alone, but given the price of a charge, if I'm going to end up doing it all over next season anyway, i might bite the bullet at this point.


    [I'm] Brian [and so's me wife]
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