subcooling

[azhogdog]

Ok I have a question, on large commercial systems with lets say, 2 or more compressors and cond. fans on one circuit. Will your sub cooling always stay the same. Lets say one compressor is on and 2 fans, subcooling is 15. second compressor kicks in and all fans,will it stay at 15. Heat load will determine how many compressors will need to be on. But on testing a unit,what is the best method of testing a system that has more than one compressor or cond. fans? Will this also apply to superheat?

[techrider]

I have alwats been informed that the only proper way to check for a units subcooling and superheat was at full load. If it has two compressors, both running fully loaded, if unloaders are on system. And you need to try to maintain desired saturated condensing pressure and temp for your refrigerant and system application.

[azhogdog]

So if there is not enough heatload or low ambients, to be calling for all compressors you could bring on the compressors disable a fan to get your head pressure up,let say r-22 to about 250lbs. ?

[techrider]

Low ambient makes checking a system you have not worked on before a little more interesting. Others may disagree but I try to maintain as constant a liquid line temp as possible to the txv pending manufacturer specs. Most R22 systems with 40 degree coil run around 100 degrees where refrigeration systems running -20 coils shoot for closer to 90 degrees. Fan cycling as possible.

If system SH is in question then allow return temps to raise enough to allow for system to call for full load for long enough period for system to stabilize.

I've seen quite a few techs that like to adjust txv's but from what I've seen I personally don't think its usually a good idea. If you start adjusting better plan on not having anything else to do that day and my thoughts are why did it require adjusting. Either someone has messed with it or something has gone wrong. Without fail every valve I have had to adjust where noone had been there first has continued to degrade in the same direction as before. I will try to adjust once but not twice.

[springer ray]

Blocking the coil works good for me