How to troubleshoot a txvs on a 2 circuit walking cooler

[elgue]

Hey How u doing?

I just started working for this company that does refrigeration (most of my experience has been on Hvac residential and light commercial units) and they had me to install this condensing unit for a walkincooler with 2 evaporators (txv).

Now this is the third compressor going in in less than 8 years (2 compressors and now an Cond. Unit).

Having two coils with one TXv each,, how can I determine if one of the TXvs not working properly and letting some liquid go back to compressor?

I dont have any reading since I was just giving a hand to an old tech that just charged by sight glass and since this is my first week I dont wanna start in this company by contradicting to the knowall.

Basically He just gassed the thing by sight glass and we left. Now correct me if Im wrong 3 compressors in 8 years should be telling someone that something else is f..ed up.

But anyway, After cheking my subcooling, How can I check the superheat in each indoor coil If I dont have a service ports just after the evaporators? Or how can I see if each txv is reacting to load if there is not a service port after each evaporators?

I know that I dont have any readings but It would help me a lot if you kind a tell me what approach you would take.

Thanks

By the way, Didnt see any control other than a common solenoid valve on the liquid line and Txvs on each evaporator.

[elgue]

Im sorry Im new to the forum and I can not find the edit option. This wasnt a 2 circuit system. It was a one circuit 2 evaporators.

[mad fridgie]

This is a very common system.
Firstly you should know your suction pressure at the compressor. This is the lowest possible pressure.
You have to make a bit of a judgement call on the suction pressure drop ( how long is the run, does it have many bends, are there any valves in it etc)
When the rooms is around its normal temp, check the temp at the TXV bulb(s)
For example, comp SST is -20C, presume suction pressure drop 2C
(presumed SST at TXV bulb is -18C)
Actual temp at bulb -13C, therefore superheat is 5C.
Why the compressor is failing could be down to many things, we need more info (as much as possible)

[bernier74]

It sounds as if the majority of your experience is on the HVAC side which is a little different than refrigeration, I recomend becoming as comfortable as you can with refrigeration work, reading textbooks, and asking some of your older more experienced co-workers for advice.

Your new and you should not be too concerned about the way your employer chooses to do their work, get acustomed to this side of the bussiness and try to learn as much as you can. Ounce you are proficient enough then begin criticizing.

[elgue]

Bernier74

Hey Dude,
Are you asking me to learn without being a Critic?
That is a little bit difficult.

[elgue]

Mad fridge, so that means that I can would use the suction pressure at the compressor?
For some reason I had the idea that since we have 2 coils and 2 txv, each coil would have a diferent pressure drop.

[mad fridgie]

Mad fridge, so that means that I can would use the suction pressure at the compressor?
For some reason I had the idea that since we have 2 coils and 2 txv, each coil would have a diferent pressure drop.

Yes use the suction at the compressor as a starting point, the pressure at the position of the TXV bulb will be actually slightly higher (no one would expect you to calculate the actual pressure drop on site) with a bit of experience you get a bit of a feeling for these things.
If you have no valves in the suction (EPR, CPR) you can class the pressure at the outlet of each evap as the same.
IF the TXV are external equalised, then you can set superheat at this common point. (evap pressure drop not so important) If internally equalised and evaps are different, then you need to measure temp at TXV outlet and bulb position to give superheat.
Your other tech used the sightglass, this pretty standard but must NOT be used as the only method, a slightglass is an Aid, most of the time it is right, but not always.