VAV616
07-09-2009, 01:34 AM
Disclaimer: I am only trying to get my 15 posts in so that i may
qualify for a pro membership. I am a graduate of an Electrical Mechanic
program at a local trade school. and I have two years HVAC at local community college. 2 years as an electrical apprentice, 2 years fixing split systems at an apartment complex. and now 2 years as an entry lvl tech in UA lu 533. I work for a refrigeration contractor who used to be big in the world of Pro Stock drag racing, maybe some of you know who. 8)
I kinda got stuck in a loophole that has allowed them to use me without bringing me into the real apprenticeship. But that will happen this year and i will begin their five year school.
anyway...
Med temp walk in cooler. Not cooling , aprox 50* when i arrive.
looking at the Bohn Let721a evap i see ele defrost elements.
so i ask him, 'Is this supposed to be a cooler or a Freezer?'
He says 'Yes, sometimes it is a cooler, sometimes a freezer.' /facepalm
Upon examining the rooftop condenser i find it packed with cottonwood
and grease. So i turn it off using the disconnect which is the
"manual wirenut" style, and give it several applications of some newbright
until it is sparkly clean.
Now with a clean condenser i start it up and begin taking readings.
this is a 404a system. 90* ambient
33# 50*sh 330# about 14amps
now, the sg is not just flashing, but actually splashing, so i need to add 404 until i have a solid line of liquid going to the tev before i can really get the tev to respond properly. from here i adjust the tev to about 12* sh. now im reading about 30# 12*sh but the head is still 325# +. 404a at 120* should be about 310 at best, right?
from here i call my local refer encyclopedia at the parts house, he confirms that both the evap and the condenser/compressor are LOW Temp, to be run at -15. but this system has been used as a med temp at 30-40*.
At this point i can get the cooler to pull down to 30* quite easily and the only mystery is why the head pressure is so high, maybe non condensables?
but the next day i come back to finish up, and the cooler is off, the breaker has tripped. i find the compressor overheated and out on internal OL.
icing it down and giving it time, i come back and the comp ohms out about normal, .8 C-R, 3 C-S, 3.8 S-R. but when i hook it back up it just makes a few jerks without actualy starting, pulling about 100a. and the other wirenut in my 'disconnect' catches fire. D8
so, it appears to me that i have a locked rotor condition.
my man at the parts house lets me know the best way , rather than
just replace compressor, is to replace the whole cond rtu with a proper
med temp system. That running the low temp system at 30* causes higher comp ratios and is hard on the system. and , of course, another $12 for a disconnect. 8D
IDK if i really have any questions, but feel free to comment
qualify for a pro membership. I am a graduate of an Electrical Mechanic
program at a local trade school. and I have two years HVAC at local community college. 2 years as an electrical apprentice, 2 years fixing split systems at an apartment complex. and now 2 years as an entry lvl tech in UA lu 533. I work for a refrigeration contractor who used to be big in the world of Pro Stock drag racing, maybe some of you know who. 8)
I kinda got stuck in a loophole that has allowed them to use me without bringing me into the real apprenticeship. But that will happen this year and i will begin their five year school.
anyway...
Med temp walk in cooler. Not cooling , aprox 50* when i arrive.
looking at the Bohn Let721a evap i see ele defrost elements.
so i ask him, 'Is this supposed to be a cooler or a Freezer?'
He says 'Yes, sometimes it is a cooler, sometimes a freezer.' /facepalm
Upon examining the rooftop condenser i find it packed with cottonwood
and grease. So i turn it off using the disconnect which is the
"manual wirenut" style, and give it several applications of some newbright
until it is sparkly clean.
Now with a clean condenser i start it up and begin taking readings.
this is a 404a system. 90* ambient
33# 50*sh 330# about 14amps
now, the sg is not just flashing, but actually splashing, so i need to add 404 until i have a solid line of liquid going to the tev before i can really get the tev to respond properly. from here i adjust the tev to about 12* sh. now im reading about 30# 12*sh but the head is still 325# +. 404a at 120* should be about 310 at best, right?
from here i call my local refer encyclopedia at the parts house, he confirms that both the evap and the condenser/compressor are LOW Temp, to be run at -15. but this system has been used as a med temp at 30-40*.
At this point i can get the cooler to pull down to 30* quite easily and the only mystery is why the head pressure is so high, maybe non condensables?
but the next day i come back to finish up, and the cooler is off, the breaker has tripped. i find the compressor overheated and out on internal OL.
icing it down and giving it time, i come back and the comp ohms out about normal, .8 C-R, 3 C-S, 3.8 S-R. but when i hook it back up it just makes a few jerks without actualy starting, pulling about 100a. and the other wirenut in my 'disconnect' catches fire. D8
so, it appears to me that i have a locked rotor condition.
my man at the parts house lets me know the best way , rather than
just replace compressor, is to replace the whole cond rtu with a proper
med temp system. That running the low temp system at 30* causes higher comp ratios and is hard on the system. and , of course, another $12 for a disconnect. 8D
IDK if i really have any questions, but feel free to comment