40ton Trane chiller...

[dking]

I have a 20yr old 40ton trane chiller.
superheat on lower txv is bouncing 10 deg. From 7deg. to 18deg
We just rebuilt txv, including powerhead.
Upper txv is holding 15deg. superheat.
any clues ?

[jimbob73]

Remote bulb location?

[clgman]

The refrigerant circuits are upper and lower, not side to side, interesting !
Is it possible for the lower circuit to have restricted water flow from years of sediment build up ? Measure the pressure drop across the chiller barrel and compare to require readings, and/or plot the pump performance on the pump curve to verify GPM. Is the temperature drop normal? If you cycle off the upper circuit, and run the lower circuit, does the superheat settle down. Is the external equalizer tube functioning o.k., and the bulb is upstream of the tube. As mentioned earlier oil logging could be a problem. Good luck !

[jimbob73]

Is this an old recip cold generator with one compressor and 2 evaps? I mentioned oil logging earlier, But then I took it back when I read your first post again.

[duke of earl]

Measure the liquid line temp entering the txv and see if the fluctuation is there also. Is the condensing temperature/pressure stable? If not then it will carry over to the txv.

[Tech Rob]

My first thoughts would be either:

A) insufficient and/or inconsistent load on the lower evap
B) condenser side issues

How quickly does the superheat fluctuate? Does it go from 7 to 18 in a matter of minutes or hours?

[lhatton]

Have you punched the econ and evap coil tubes lately? I am assuming you cant isolate the upper txv from the lower txv, meaning you have two 20 ton txv's to cover the 40 ton unit. If you have rebuilt the txv and power head, I would guess that your txv body may have a flaw in it? Good luck friend

[dking]

Yes, the tubes have been punched, and you are correct the txv's are 20ton
and am not able to issolate them. txv's rebuilt, and power heads replaced.

[dking]

Well, it may all be for not because today the stupid thing is running fine.
Super heat has stabalized @ 11-12 and the oil pressure is a net 30psig

Go figure.

[duke of earl]

Possible you had an oil logging problem. Maybe the oil has come back to the compressor from the evaporator. Just thinking out loud.

[refrige-nate]

Well, it may all be for not because today the stupid thing is running fine.
Super heat has stabalized @ 11-12 and the oil pressure is a net 30psig

Go figure.

maybe you have the same problem as me...impatient!:D when you rebuild and reinstall a txv it takes quite awile for it to reach equilibrium. hunting txv's drive me nuts!

[dking]

maybe you have the same problem as me...impatient!:D when you rebuild and reinstall a txv it takes quite awile for it to reach equilibrium. hunting txv's drive me nuts!

Yeah, its kinda drivin us nutz, its been 2wks and its still huntin. Today for instance, when I checked it in the morning...fine 10-12 deg S.H....So we call trane tell em don't bother commin out. Of course in the afternoon is was back to 5-7 :-(....I think we are going to just let it ride for a few more days and see what happens.

Thanks for the input.

(oh yeah, we also thought the oil was out in the evap, and it was but its back now). One thing I don't think I mentioned before was the loss of net oil pressure after we had it apart......

[emcoasthvacr]

Between the liquid header & TXV, there is a point "X" that moves back & forth as the load fluctuates to ensure there's enough of the evaporator to warm the gas to the superheat setting of the valve.

Point "X" is determined by the DIFFERENCE in temperature (superheat) between the evaporating temperature and the gas temperature at the sensing bulb --- this is important since regardless of evaporator or suction temperature variations, the amount of superheat remains almost constant to prevent liquid from entering the suction line.

[dking]

Thanks to all who replied. the one in question has been resolved.

BTW, I have 16 of these 40 ton tranes (and 2 25 toners). Keeps us busy.

[clgman]

Please bring us up to date on what was done to correct the problem !!!