Commisioning

[Leon_dawson2008]

Hi guys,

I am a level 3 qualified engineer on the isle of man that has only been in the trade for 5 years. My problem is that since I started I have been in a two man team me being the second man, and after I finished college I naively overruled a lot of what was taught to coincide with the advice of my supervisor.

He was what you would call an old school engineer, he has now retired and I am finding it extremely difficult as I now am on my own and look after anything from a supermarket pack to a VRF system or even bottle coolers and small ice machines, I have been on my own for two years and still do not get a lot of call backs although I know I am doing some aspects wrong

I am very happy with the electrical side of my work but am finding commissioning extremely difficult. I was taught by my boss at the time that to charge a system you use the evaporating temp that you require ie for a deck it would be 6 degrees c, then subtract ten and this will give you your evap temp and that is what to charge to on the gauge so about -4 which is about 3.2 bar off the top of my head.

Now I know people will be tutting when reading this and even when I read back myself I know it's wrong. I have just got a comparator but cannot remember how to use one I know that I need to take temp at the comp discharge Nd the temp from the evap entry but can't remember what to do next.

Do I subtract the two figures to get the superheat ? And how do they relate to the line on the comparator?

I do realise that this may shock people that I have lasted this long doing as I do but I am a decent engineer I can wire a controll circuit and strip a comp but this just seems to escape me and was just after a little guidance if possible

Thanks

[frank]

Leon, I think that you might get some good information by reading this thread - it's aimed at helping newbies to understand the basics.
http://www.refrigeration-engineer.com/forums/showthread.php?19701-Refrigeration-101

[Luke.G]

Hi Leon,
We all need help & guidance at times. Yes you are right in saying that roughly the evaporating temperature should be -10 below the set point temperature but i wouldn't use the diff to charge the unit....
If your charging a condensing unit with a sight glass, you could charge to a full sight glass ( knowing that your TEV is not under feeding or over feeding or any restrictions in the system) and then check the superheat.
As you should know you can only check superheat on systems with a TEV....
to do this you: take your suction pressure, lets says R134A 1 bar back pressure, relate that to your comparator which is -10
then take your suction temperature, using a independant thermometer; say your getting a temperature of -3
you then minus these temperatures to give you a Td of 7k your superheat should always be between 5-10k depending on glide.
also another method is subcooling which is roughly the same as superheat but you do it just after the condenser so liquid, but then your looking for between 2-5k for that

hope this helps mate

luke

[Santa Fridge]

Hi Leon,

Guess you need some further training.......... ring or email me and I will go through the procedure with you.

Regards

Andy at Grimsby Institute

[MICHAEL TSIVIS]

Hi Leon
You Need to measure your discharge temp leaving the compressor about 100mm from service valve and then subtract the saturated condensing temp which is your gauge pressure converted to temp Eg 55 Degrees celius minus 38 degees SCT gives you 17K superheat
Cheers

[hookster]

Hi Leon
I would like to just tell you how to do this but I do not think it will aid your learning. With a Level 3, I assume you mean NVQ. Not to knock you or your training establishment but this is where the Not Very Qualified jokes come from.

I would suggest that you join the Institute of Refrigeration (IOR) Service engineers section. This will be the best £30 a year you can spend. http://www.ior.org.uk/ior_filter_technical.php?r=34EM3M4NAE

The information then available to you is excellent and have a look at the Service Matters Technical information.

[river1710]

did u get the answer to your Q?

[mathias]

Leon,
Just don't give up - I am directly opposite to you I am retiring soon and will spend my time building training video's to help teach you young guys thru my experience! I have been a factory rep for 5 manufacturers so visit my web site and tell me what u need. hvactrainingcoach.com