Noob Tech.. noob mistake??!!

[jurtaman]

First, a little background on me and my project.. I skipped out on the schooling and got my 609/608 universal certs qith a quick course. Now learning from older experimental (for me) units and this website. I understand all the basics (or at least i think I do) but have a few questions and an issue with my project..

First about the project.. I'd say about a 10x15 refrig. cooler for a family owned restaurant. I'm taking over our current refrigeration guys job (I work for the company they wanted an internal refrig. guy) He has 2 evap/condenser systems cooling the box. One had burned out end of last summer and with temps rising I thought it would be a good fix. We had another used condensing unit of I believe similar characteristics (240/1 3/4HP R12) sitting in our barn so I tried to see what would happen If I replaced the burned out one with it.. and so begins my journey..
I used the best practices I could here is what I did..
1.) Disconnect TXV and flush out lines and the evap. with that r11 replacement flush stuff.. about 1/2 can using dry nitrogen as a flush gas..

2.) Change oil in hermetic compressor (through rotolock hole) since the tech who pulled it didn't close the valves and it was stored in a damp dirt-floor barn basement for like a year or two! Used AB oil since it's experimental and POE was more $$.. 24oz added used measuring cup (through rotolock hole)

3.) Sealed up system pressurized up to 150 nitrogen (per low side tag) and bubble checked (got a h10-pm on the way.. hope u guys are right!) Appeared to be no leaks.. Oh yeah new LL drier and SL drier.. Large ones just in case..

4.) Pulled 500 micron vac (no hold) added n2 to above atm, pulled another vac (no hold) added n2 to above atm, then pulled it down again to like 400. Never got it to hold under 500 and was too impatient to see how high it would rise.. explaination in other thread called "new tech, new equipment, new problems!" and time.. Did this while enjoying a meal in the restaurant (checking on setup every now and then).. Also.. didn't wait the 1hr each time for to the nitro to "absorb" the water. Does this _really_ happen i thought it was to help sweep the moisture out while you vac all the molecules again.

5.) added 4lbs liquid 409a (basically until sight glass is full) and fired it up. Tweaked my controls to get it to work. Kicks ass the other unit in the box is shut off now cause it was pretty much usless (box temp getting over 55 overnight) ok so it's working great but not right.. here are my issues.

High head pressure .. 250PSI not happy with it 409a I want to see ~150psi.. max on unit says 235! RLA at 7 I'm running 8. Discharge temp cooks cookies!
Other than that unit does it's job well.. evap temps go down to like 15 when the box stays closed overnight. Coil doesn't brick cause the other guy stuffed the thermostat bulb in the coil fins so when it starts to brick airflow reduces and it gets cold enough to shut off compressor.. defrosts through like 15 degrees diff (until coil is clear) and starts back up. Box temps 32-40 and dry. works great on my 1 unit alone!

Sounds like air what do u all think? should i lose the airbound 409 and charge virgin again? is air my problem? green eye in sight glass.. Let's hear some opinions.. Also why are HVAC units mostly rates with tons/BTUs but refrig. stuff seems to just go by HP?? (again.. to me at least)

Be easy on me.. -Noob

[hvac69]

Superheat and subcooling readings?

[jurtaman]

barely any superheating (via TXV) to try and keep the compressor cool and I'll have to get back at you for SC honestly never checked.. that high side is HOOOOTT!! I'll get 2 you on monday..

[jpsmith1cm]

GO TO SCHOOL.

This isn't a trade for dabblers and learn-as-you go guys.

You MUST have a SOLID understanding of the basics of the refrigeration cycle before you are going to be able to properly diagnose problems with it.

Let me put it in another context for you.

If you build a house, what happens if you don't have a good, solid foundation? The house crumbles.

The same goes for your education and career in HVAC/R.

Build a solid foundation through education and understanding, not through experimentation and tomfoolery.

[jurtaman]

Obviously that would be the best choice but don't have the time. Experience is what i need anyways.. have plenty of units to dabble with in the 'ol barn can't break something that's already broken! But if you fix it and it lasts there is something to be said

[jpsmith1cm]

Obviously that would be the best choice but don't have the time. Experience is what i need anyways.. have plenty of units to dabble with in the 'ol barn can't break something that's already broken! But if you fix it and it lasts there is something to be said

[jurtaman]

and u never told me if u thought it might be air. I bet the condenser is full if it... After i fix the useless 2nd unit (If i can) I'm going to leak check when i get my h10, re-vac the system, for a while...., and try again with fresh stuff. But comments are welcome as I have a week before i get the h10

[jpsmith1cm]

and u never told me if u thought it might be air. I bet the condenser is full if it... After i fix the useless 2nd unit (If i can) I'm going to leak check when i get my h10, re-vac the system, for a while...., and try again with fresh stuff. But comments are welcome as I have a week before i get the h10

Theoretically possible, but without a subcooling reading, it is impossible to tell what the cause of your high head pressure is.

Since you made at least a perfunctory attempt to evacuate the system, I'm *assuming* that the amount of air in the system is minimal and won't affect system operation in any real, measurable way.

[Makinhole]

I have been fishing my entire life. I grew up living right on a river. I catch fish where ever I go, some say I could catch fish in a mud puddle. However, when I go to a new river for the first time, I hire a guide. I pay him my money and I go along for the ride. Maybe you need to hire a guide?...good luck...

[timebuilder]

Obviously that would be the best choice but don't have the time. Experience is what i need anyways.. have plenty of units to dabble with in the 'ol barn can't break something that's already broken! But if you fix it and it lasts there is something to be said

Yes. That something is:

"a broken clock is right twice a day."

[Control Man]

"a broken clock is right twice a day." If your still around to watch it

[jurtaman]

It would be nice to hire a guide but my boss wants to stop paying the guide and pay me, and the guide was never too informative anyways.. he never listened to what i had to say because he always assumed i didn't have the capacity to understand his "complicated" trade. I think he never answered my questions because he himself did not know...
OK... Simply put it's a system moving heat... but you could complicate it down to the atomic level it's all how deep in theory you want to go.. I'd say i understand microns/vac, pressure/atmosphere, PT Charts(even split), latent heat (evap) vs. sensible (superheat), la tee da could go on better off saying I am unfamiliar with (and looking into currently) Electrical consumption (Watts) vs. cooling capacity (btu) and the adjustments to maximize efficiency, effects of lets say big coil/lowCFM or small coil/high CFM, humidity in the box, the diff enthalpys of diff regrigerants and why they are used in their respective applications, and maybe oil circulation and other oil related concerns too. Those are my areas of current study. This place is great to learn, the old units in our barn are great to experiment/frankenstein on for cause and effect, but it's difficult if a "guide" answers with something less related to the question or the general concensus is unclear in a forum, unlike the _clear_ opinions of the H10-PM on here Still tooling up!!!

[jpsmith1cm]

Tool talk in open forums is one thing, detailed tech talk is another entirely.