rtaa 140

[milkyway]

hello guys and gals., i am working on a rtaa 140 that was built prior to 94.,
1991 actually, anyways i am doing a high side repair, has old ucp 1 controls., (the blue one), i have a set of gauges hooked up , looking at low side, doing service pumpdown, and the danger or the question that i have is why am i not supposed to drop below 20* and if i do what happens? also i know that if it does fall below 20* to pull 1f15, .,
am i going to need to recover the left over gas or is the evap going to hold 100%?

question 2

can i perform a pumpdown on 1 circuit and have the other run.,
i am not thinking so.,
can i get some inside info?

[Healey Nut]

why am i not supposed to drop below 20* and if i do what happens? also i know that if it does fall below 20* to pull 1f15, .,
If you run a screw compressor into a vacuum you can kiss the compressor good bye . no refrigerant to cool the rotors the rotors swell metal meets metal and its all over but the cryin'
Yes you need to transfer the rest of the gas to the low side unless you dont care about EPA regs and yes it can hold the whole charge just like the high side can .

[cperk]

You can't pump it down to do a highside repair. Think about it for a second, your going to have liquid line service valve closed, so where is the refrigerant going to be trapped? You can transfer the gas, with a recovery machine, to the evap.

[Healey Nut]

You can't pump it down to do a highside repair.

SSsssssshhhhhh dont tell him everything , sometimes it helps to learn on your own .

[cperk]

You can't pump it down to do a highside repair.

SSsssssshhhhhh dont tell him everything , sometimes it helps to learn on your own .

Sorry graham.:bsing:

[Healey Nut]

Sorry graham.


Forgiven ...NP

[ga1279]

Mlkwal1- Yeah, funny thing about screw compressors they just don't like getting pumped down too low, just like scroll and for the same reason. You may read 20# on your suction gauge on the suction line,but the pressure between those screws (male and female) is much less. You will end up damaging that sucker real bad if you let it get too low. You said it was a 140 ton unit yes you can pump down one circuit while the other one runs. I am not sure if the true menu pump down will let you. I haven't used menu 19 service PD in years as all it is amounts to time function only, no pressure shut down and you only get one shot (according to the manual). Don't bother trying to put a gauge on the liquid line service valve as I'm sure you already know there backwards, meaning you are reading upstream pressure not downstream at the 1/4" flare fitting. Lets just day you want to pump down circuit "A" With chiller running normally go into menu 1-item 1A circuit lock-out and enable circuit for "A". It will shut down momentarily. Go to the back of the bus and close the liquid line service valve for circuit A. Go back to menu 1-item 1A and disable the circuit lockout for "A" it will restart again soon. Before it starts install a very accurate gauge to the upstream shreader port on the suction service valve. Short a hose as possible were you can still read while standing by the control panel. Observe gauge pressure dropping. When it gets to 20#, not 15, not 17 and damn sure not 10#, put the chiller control in the stop reset mode. when machine stops, put compressor A in the circuit lockout mode (enabled) Also close your suction service valve. Don't know what your planning on doing, but this will clear the liquid out of the evaporator and suction line. You will still need to recover the remaining vapor with a recovery system, depending on which one you have it shouldn't take long. Good luck and Hey don't forget to VOTE tomorrow-GEO:playing:

[milkyway]

You can't pump it down to do a highside repair.

SSsssssshhhhhh dont tell him everything , sometimes it helps to learn on your own .

u guyz r silly as hell.,lol ., i know graham doesnt like to share all the tricks.,
i am repairing a leak on the condenser coil, one on each circuit
actually i was reading rtaa sb10 , page 7., high side repairs, and it does not say enable service pumpdown.,lol., anyways it does say to open eex 100% and pull plug to remain open so that gravity and diff pressure will flow liquid to evap., im thinking that after certin amout of time that the eev needs to be closed after the system equalize?? if not the high side will still be open?im i wrong?

[jayguy]

u guyz r silly as hell.,lol ., i know graham doesnt like to share all the tricks.,
i am repairing a leak on the condenser coil, one on each circuit
actually i was reading rtaa sb10 , page 7., high side repairs, and it does not say enable service pumpdown.,lol., anyways it does say to open eex 100% and pull plug to remain open so that gravity and diff pressure will flow liquid to evap., im thinking that after certin amout of time that the eev needs to be closed after the system equalize?? if not the high side will still be open?im i wrong?

running the other circuit will keep the evaporator fluid temperature down and that will help keep the evaporator circuit that you are working on low and help transfer the fluid. eventually, you will have to close the liquid line service valve (and make sure that it is tight!) and transfer the rest with your recoery machine.

[ga1279]

mlkwal1- Only got bits and pieces of your original post as my 19 year old IT person has tried to make my life simpler by adding a software program that pre-reads post and puts them in quick file with only the highlights coming forth. So until I filtered out his program I did not see all of your original post. There are things that can be done to move the refrigerant from the condenser to the evaporator and yes some do involve the opposite circuit compressor, but we're traveling down a road I'd rather not go. Anyone have any ideas as to how to get your personal 19 year old IT person out of your house and in the military so he can unload all his programs on them. Again, tomorrow, get out and VOTE if you haven't already-GEO:toetap:

[latchingfault]

Iv pumped an rtad into a vaccum... like said earlier I did a service pump down, where the comp will run for 1min (think)... well musta been bit short... replaced my part... turned it on... hasnt missed a beat.. think the lil comps are bit tougher (chhp comps???)

[Healey Nut]

i know graham doesnt like to share all the tricks.,


I dont mind sharing the odd trick or two . I just dont like to give everything away . If everyone on here just did everything by asking or reading how to do it in a book very little is learned . Sometimes you have to sit down study the problem yourself and come up with an approach on how to fix it . Then you have to have a go , if it works then bingo you learned, if not then try something else , get the grey matter engaged . Its too easy to ask someone else to show you or tell you . But at 2am when your on call and the pressure is on you have to think on your feet .
I would have to say that 80% of what I know has been learned this way . Im not a good book or instructions person . I prefer to get in there get dirty and try .
As long as no one gets hurt in the process then Im good with that . Ive been doing it this way for 30yrs now and it has served me well .
Have I made mistakes ....... Hell yes lots of them , but Ive learned more from those mistakes than any book could ever teach me .

[ga1279]

I think you put it quite eloquently, I also have 30++ years of commercial / Industrial HVAC experience. While I was employed at Trane I spent several years training apprentices from day one. Even in the early stages who could tell who was career minded and who were parasites. It is one thing to be able to tell how a system works on paper and quite another on Superbowl Sunday when 2 out of four main chillers aren't coming online the control guy has the chief engineer in his pocket, Because his EMS is definitely not causing this issue. The chief is doing a burn because they just called you out against the control organization wishes. They are saying that this so and so couldn't fix squat. Mean while you slowly walk up to his digital output section and do a little wire finagling and zoom there up and running. I kind of go in cycles here on this site. Right now I think I just want to sit back and read from the other more learned individuals.-GEO

[milkyway]

totally agree w you., this level of ac work is something special i think.,and if all it was was to just read and fix,. thats not really fair to someone who has been in the field fo 30 + years.,.,most mechanics have worked for the factory for some period of time and that helps the learining process a little easier., always have someone to call on for an answer or to bail them out., the real pressure comes when there is no one to call., only urself.,.,now that is scary., there is soo much literature on these machines, have to be fimualr w books, refrigeration cycle., oil system., controls., modules., sensors.,ect., holy cow., and that doesnt include summitt.,., me personally i dont have anyone to call on ., and if i cant fix it i have to call factory and there goes my lively hood., and this site is termendous,. not because it tells me exactly how to fix a problem but because the threads are full of info if one knows how to understand what is being explained., i am much appreciated for the info i receive from reading., without reading i would have nothing., but it still takes years and years of reading to b really good.,

The chief is doing a burn because they just called you out against the control organization wishes.
not sure what this means?

[ga1279]

As the great Paul Harvey used to say. The chief Engineer had listened to the assistant chief's advice and called me out rather then wait on the factory rep to come out on the following Monday. The control tech, from the same corporation, different division said that was something that was against the rules of their contract. While I was trying to get the big picture in mind, having never been to this huge site before. Like Oddball used to say in Kelley's Hero's "I'm feeling a lot of negative vibes here". So the Chief was just about to throw up his hands and send me and my friend (the assistant chief) down the road together. That's when I noticed neither chiller had an "enable signal" from the D/O module of the controller even though there was a command on the front end. A little re-wire and the assistant chief starts looking like the genius that she is. And now you know the rest of the story.:ghug:.... Thank You Paul Harvey and Good Day.-GEO