Will you check my data please?

[Windseeker]

I was re-reading the 101 fundamentals on Subcooling and Superheat and decided to take some readings. This is in an older Carrier Split HP 3 ton R-22. It's going to bre really hot this week. Thought I would double check the system. Your expertise is appreciated.

I'm thinking this system is undercharged because of the high Superheat (40 Deg). Also, the vent temp seems high to me. Does it make any sense that the condensing Hi line temperature is higher than the saturation temp? Perhaps there is a problem with the gauges?

Any input is greatly appreciated. Thanks.

[The Viking]

OK,
To determine if your system got the correct charge the best value is the sub cooling. Unfortunately for you imperial guys sub cooling is measured in Kelvin (K), as it happens the "stepping" of Kelvin and Celsius (C) is the same i.e. 10K-5K=10C-5C. NOTE: 10K does not equal 10C.


But first a question, by "Condensor Low temp", are you referring to the temp of the liquid line leaving the condensor?
If so the saturated temperature of R22 @ 135 psi is 25ºC and your liquid line temperature translates to 27.2ºC, giving a sub cooling of -2.2ºK (the refrigerant leaving the condensor is therefore superheated and not sub cooled, there is in other words no liquid)

Therefore your system is short of refrigerant.
(Assuming your measurements and my assumptions are all correct)



.

[Windseeker]

Thank you very much for the review. The system was charged and doing much better. I did not know you could make it "Rain" inside your evaporator unit with low refigerant. I always wondered why there was water in the drip pan. I just thought the trap was clogged.

Just when I think I understand this, I get humbled. I have to ask about the Sub-cooling measurement. I thought you were supposed to add refrigerant just to the point where liquid is not returning to the compressor by measuring the Superheat. An undercharged system would have High Superheat and Low Sub-cooling right? Are you not suppose to add refrigerant until you have a Superheat of 15-20 Deg F? If I was adjusting the Sub-cooling, how would I prevent an overcharge or liquid return? Also, where do I stick my temperature probes on the lines? If measuring Sub-cooling, would it be the exit of the condenser, or the entrance to the evaporator?

[The Viking]

The superheat is controlled by the expansion device and are therefore not reliable to use for charging purposes.

Yes, for subcooling you measure the refrigerant leaving the condensor.

[Windseeker]

So, If my sub-cooling specs calls for 20 Deg F and the refrigerant is adjusted for that, then the proper charge is in?

Is it a problem if the temp probe is tied to the outside vs. inserted into the stream? It's an indirect measurement.

I guess I wish I understood why you would measure at the condenser exit and not the evaporator inlet since this is where the action is happening and the total heat loss has occurred. Does not make sense at the moment,

[Brian_UK]

There is a training video from Sporlan if you want to brush-up the skill set...

http://www.sporlanonline.com/sporlanpt320.wmv

[Windseeker]

WOW! This is great! Thanks! What else do you have up your sleeve?