Tech needs to pick your brain. - http://www.hvacmechanic.com/ Forums
Original message
| SvcGuy
 |  "Tech needs to pick your brain."
, posted Fri 17 Aug 19:45  
Ive got a system that continues to freeze up. This is a new construction install by another company that sat empty until the house was finally rented a month ago.
First call was a "freeze up". A differant tech found a leak at the outdoor cap tubes. Fixed leak, pulled 400 microns and charged but could not get suction pressure above 62-64. It froze up again, same tech went back.He couldnt get decent suction pressure and thought maybe moisture was freezing at the TXV causing partial restriction.
Distributor did not have a TXV so they gave him a coil with a piston. He kept the piston and chose not install a new TXV. (dont ask me why?) A week later it froze up again.
Enter me.....upon arrival system froze. Calculated CFM using strip heat method. CFM is 1170 on a 3-ton system.
Return temp is 85
Outdoor temp is 90
Subcooling is 24
Superheat is 40
Suction pressure is 60 with 240 head. Considering I have an 85 degree return temp that suction pressure is real low. I think that once the return temp gets to a normal temp the suction pressure is falling and making it freeze.
My subcooling is high too.
So Im thinking of changing the piston to a larger size even though a 065 appears to be the correct piston and that is what is installed in the coil.
Im kind of dumbfounded.
Outdoor model#upmd-036jaz
Indoor model#ubhc-17jo6nfh
Any thoughts? Am I missing something?
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Replies:
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| gigahurt
| "Re(1):Tech needs to pick your brain." , posted Sun 19 Aug 10:57
I would firts ask if the condenser has a cpper spun drier in it. If it does then it most likley came apart internally. I have seen it many times
HVACR You know like hvac with an r on it.
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| | SvcGuy
| "Re(2):Tech needs to pick your brain." , posted Sun 19 Aug 20:17
I checked the drier about thirty minutes into the run time and it didnt have any "temp drop" across it.
I called this guy tonight to let him know I was coming out tomorrow and he said it is frozen again.
Usually when I look for a restriction, I look for frost but If its partially restricted in the condensing unit should I just be looking for a temp drop across some part of the condensing refrigerant circuit?
Would a kink in the suction line cause high subcooling?
Or is it most likely on the Liquid side?
Thanks for all the good thoughts and Ideas.
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| Gregg Harris
| "Re(1):Tech needs to pick your brain." , posted Sat 18 Aug 10:06
In re-reading the post did you say that the EC had been changed from txv to a piston coil? If this is the case look for the restriction upstream from the coil, ad service T on liquid line this will give you instant answer for restriction in liquid line between condenser and coil.
"It takes less time to do something right the first time than it does to explain why you did it wrong."
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| Gregg Harris
| "Re(1):Tech needs to pick your brain." , posted Sat 18 Aug 09:38
I would be looking for some tipe of restriction, high subcooling low suction, refrigerant is backing up in the liquid line, suction pressure is dictated by the evaporator if the refrigerant is not entering the coil in a liquid state and having a change of state, and absorbing heat the suction pressure will be low. Distributor on coil could be cloged check for frosting.
"It takes less time to do something right the first time than it does to explain why you did it wrong."
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| bigglenn357
| "Re(1):Tech needs to pick your brain." , posted Fri 17 Aug 20:34
I ran into this 1 time on new construction.The line sets before being hooked up sat outside without being capped.So after install guys hooked up I had to go start unit and check out.Had same thing happen and seemed there was a restriction but couldnt see one,so finally I torched off the piston holder from liquid line and on the screen was a shitload of dirt.Cleaned out-sil-fosed back,vacummed system and ran like a champ after that.Just a thought if all else fails
Big Glenn
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| bubbad
| "Re(1):Tech needs to pick your brain." , posted Fri 17 Aug 19:59
Did you check the suction line for kinks?
bubbad
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| fitter597
| "Re(1):Tech needs to pick your brain." , posted Fri 17 Aug 19:59
Liquid line temp
suction line temp
discharge air temp
Lets get all the goods and try to figure it out
fitter597
Pipefitters Local 597
" We do it right the first time"
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| | SvcGuy
| "Re(2):Tech needs to pick your brain." , posted Fri 17 Aug 20:09:
Thanks for the reply`s.
The tech before me crawled the whole attic looking for kinks. Im trusting him that its not.
OK, 30 seconds after starting: 38/190 68*SL 74*LL
Two minutes into runtime: 50/195 77*SL 81*LL
Five Minutes into runtime: 55/210 77*SL 82*LL
Fifteen minutes: 57/225 73*SL 82*LL
Thirty Minutes: 60/240 72*SL 87*LL
Air temp is 84* at return plynum, 64* at supply plynum
Fan is on High speed.
Thanks Guys.
[this message was edited by SvcGuy on Fri 17 Aug 20:11] |
| | fitter597
| "Re(3):Tech needs to pick your brain." , posted Fri 17 Aug 20:38:
i vote for a internal plugged condenser, due to liquid line temp being lower than the outdoor temp after 15 mins, or you have a restriction in the condenser. are there any driers in this system, maybe in the condenser? you are stacking too much in the condenser has to be resricted
Pipefitters Local 597
" We do it right the first time"
[this message was edited by fitter597 on Fri 17 Aug 20:39] |
| | SvcGuy
| "Re(4):Tech needs to pick your brain." , posted Fri 17 Aug 21:47
Thanks for the reply`s
The condensor does have a drier(3rd one) and it has less then one degree temp draw across it.
The LL is basically at ambient....87*
Its crazy how this thing takes a half hour for the suction just to get to 60.
Im wondering if maybe the SL is kinked where it runs over the block and into the attic.......I doubt he checked that.
What do you guys think of upsizing the piston?
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| | fitter597
| "Re(5):Tech needs to pick your brain." , posted Fri 17 Aug 22:38
Bro, it's at ambient after 30 mins, should be above after 30 seconds, it's a restriction for sure, just where it is, is the question, i still think it's in the condenser, didn't someone make a repair on the "captube outside"? but could be in the line but the liquid line temp is scary. have you checked the drier temp difference after 15 mins of running? try that too, also the piston might help alittle but it's not the cure,and if your going to bust into the coil, put a txv on it
I like calls like this, your going to feel like the man when you figure it out, stick with it and always remember the basics, rules are simple in refrigeration, and never take another tech word on what he did, check those lines for yourself and keep us in the loop.
Fitter597
Pipefitters Local 597
" We do it right the first time"
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| | bubbad
| "Re(5):Tech needs to pick your brain." , posted Fri 17 Aug 21:56
I would check the suction line temp right at the indoor coil, and then at the outdoor service valve, and see if there is much of a difference.
bubbad
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