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Poodle Head Mikey
08-14-2016, 05:12 PM
Refrigerant: R-407C
Type of Metering Device: Alco TCLE
Ambient Temperature: 96
Head Pressure: 245 lbs. (107)
Condenser Air Out Temp: 106
Liquid Line Temperature: 91
Liquid Subcooling: 15
Suction Pressure: 54 lbs. (34)
Suction Line Temp: 65
Suction Superheat: 31
Return Air Temperature: 74
Evaporator Leaving Air Temp: 57
Evap air ∆T: 17

What is wrong with this system? What should I do to fix it?

Blake79
08-14-2016, 05:49 PM
Find the restriction

Saturatedpsi
08-14-2016, 05:49 PM
Since when do you need to ask how to diagnose refrigerant system issues?

:confused:

Trick question?

BNME8EZ
08-14-2016, 06:03 PM
Since when do you need to ask how to diagnose refrigerant system issues?

:confused:

Trick question?

That was my thought, maybe he's starting to get Oldtimers disease, you know when you forget to remember what you just forgot. lol Shouldn't laugh it's not funny. I'll walk into a room and forget what I went in for, it's terrible when it's the bathroom. Or go all the way out to the truck only to forget what you wanted, so ou grab some stuff and head back only to remember once you get back downstairs.

Sorry Mikey what do you want to fix?

Air flow?
WB?
What else do we ask DIYers or newbies for that he hasn't posted?

Poodle Head Mikey
08-14-2016, 06:03 PM
An interesting diagnosis - please tell me how you came to that conclusion.

PHM
------




Find the restriction

Poodle Head Mikey
08-14-2016, 06:14 PM
How it started:

About a week or so ago I woke up before dawn and thought: "there is something wrong". So I laid there and I listened and I could hear my two condensing units running outside.

One is a R-410 Goodman 018 condenser piped to an 024 Unico air handler.

The other is an early 1980's Coleman 5 ton condensing unit with the 15K BTU rotary compressor I salvaged out of an old window box grafted into it. Oil is a blend of mineral, POE, and Supco 88. Refrigerant is R-407C.

The upstairs unit cycled off - the 1st floor unit continued to run.

That happened several times over several nights and each time I concluded that it was the frankensteined Coleman which was twitching my mechanical intuition alarm.

I did nothing about fixing it but I did note that on 95+ days the 1st floor temp drifted from the 73 setpoint to 74, and sometimes even to 74 by late afternoon.

Today I only had two No-cooling!!!!! calls to do so this afternoon I set up my 8000 CFM work fan and set up the test gear on the old Coleman.

Then I posted the data so as to be able to discuss it all with you all.

It's not a trick question - just a question. <g>

PHM
-------



That was my thought, maybe he's starting to get Oldtimers disease, you know when you forget to remember what you just forgot. lol Shouldn't laugh it's not funny. I'll walk into a room and forget what I went in for, it's terrible when it's the bathroom. Or go all the way out to the truck only to forget what you wanted, so ou grab some stuff and head back only to remember once you get back downstairs.

Sorry Mikey what do you want to fix?

Air flow?
WB?
What else do we ask DIYers or newbies for that he hasn't posted?

billygoat22
08-14-2016, 06:32 PM
oversized evap?

Blake79
08-14-2016, 06:37 PM
LL cooler than ambient, low condensor split, low SP high SH

heatingman
08-14-2016, 06:51 PM
Refrigerant: R-407C
Type of Metering Device: Alco TCLE
Ambient Temperature: 96
Head Pressure: 245 lbs. (107)
Condenser Air Out Temp: 106
Liquid Line Temperature: 91
Liquid Subcooling: 15
Suction Pressure: 54 lbs. (34)
Suction Line Temp: 65
Suction Superheat: 31
Return Air Temperature: 74
Evaporator Leaving Air Temp: 57
Evap air ∆T: 17

What is wrong with this system? What should I do to fix it?

With the LL below ambient, you likely have a restriction in the condenser.

Find the liquid header in the condenser and check the feeds into it. The coldest one will be where the issue is coming from.


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knave
08-14-2016, 06:55 PM
Why is the condensed liquid cooler than outdoor ambient?

Head pressure seems a little low for the ambient.

Can you adjust the txv superheat?

knave
08-14-2016, 06:57 PM
Also condenser air out, is usually 1 or 2 warmer than condensing sat temp in my experience. Must be because of the discharge superheat.

heatingman
08-14-2016, 07:18 PM
Wait a minute - is this the set up that you have with an EPR valve at the evap?


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Poodle Head Mikey
08-14-2016, 07:36 PM
And also: I had forgotten something -

The evap on this system is a 3 ton horizontal A. I forget the brand right now but they come is an bright dimple-finish 'aluminum' case. Galvalume maybe?

I originally set it up with an Alco take-apart TXV - a TCLE with a 2 ton cage assembly in it. But later I installed a 3 ton non-adjustable Sporlan TXV - I forget why now.

The condenser approach is essentially zero - so I can try easing the subcooling up and forcing more capacity out of the valve with losing too much to higher head pressure. Obviously I can't adjust the TXV at this point. <g> But the SSH is clearly too high so something has to be done.

I was just curious what you all suggested.

knave
08-14-2016, 07:56 PM
Cooler than ambient LL.....
measurement error, or restriction in od unit?

Poodle Head Mikey
08-14-2016, 08:08 PM
No: I scrapped the EPR valve when I downsized the compressor.

PHM
-------



Wait a minute - is this the set up that you have with an EPR valve at the evap?


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heatingman
08-14-2016, 08:08 PM
PHM,
Unless you have a subcooler, or a water cooled add on condenser , which neither would surprise me, you have a restriction in the condenser causing pre-flashing in the LL- so whatever subcooling you think you have - you dont have.


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Poodle Head Mikey
08-14-2016, 08:35 PM
Got a new set of numbers for you - with new (different) test gear.

15,000 BTU compressor in a 60,000 BTU (rated) condenser
36,000 BTU evap coil
Refrigerant: R-407C
Type of Metering Device: 3 ton TXV (non-adjustable)
Ambient Temp: 88
Head Pressure: 220 (99)
Cond. Air Out Temp: 95
Discharge line temp: 133
Discharge SH: 38
Liquid Line Temp: 88
Subcooling: 7
Suction pressure: 54 lbs. (34)
Suction Line Temp: 62
Suction superheat: 28
Return Air Temperature: 72
Evap. Leaving Air Temp: 55
Evap air ∆T: 17

So? How about now?

mythreeegirls
08-14-2016, 08:38 PM
Good, useful information. Thank you!

Snapperhead
08-14-2016, 08:46 PM
With your franken creation , id probly replace txv with adjustable type

I like the big ass condenser coil , Ive done that once on a freezer I converted from r12 to 404 and added a second cond coil in series with its own fan , runs friggin fabulous

knave
08-14-2016, 08:47 PM
What is the suction line size. If low velocity and high surrounding ambients, could be gaining 5 to 8 from evap to condenser. The indoor airflow is likely higher than 600 CFM which COULD explain the low 🔼t

knave
08-14-2016, 08:50 PM
You stated three different known oils. What are the chances of an oil logged evap?

Smaller compressor with larger evap and possible oversized suction line.

HellGato
08-14-2016, 08:51 PM
Mikey, what was that 3 ton TXV rated for? R22? since it is now R-407C inquiring minds want to know

garyed
08-14-2016, 09:21 PM
Since your compressor is so undersized for the coils, my guess is you're going to have to keep adding gas to see if you can fill up the evaporator & get the SH down. Whether the SC should be 0 or 25, you really have no idea with that system so i would do some charge experimenting first before assuming any type of the restriction. You might never get it any better but If adding gas doesn't help then you could check for possible restrictions. How many CFM are you moving over that 3 ton coil? You might want to get the return & supply humidity or WB & calculate the actual btu's you're getting with that system.

heatingman
08-14-2016, 09:32 PM
Got a new set of numbers for you - with new (different) test gear.

15,000 BTU compressor in a 60,000 BTU (rated) condenser
36,000 BTU evap coil
Refrigerant: R-407C
Type of Metering Device: 3 ton TXV (non-adjustable)
Ambient Temp: 88
Head Pressure: 220 (99)
Cond. Air Out Temp: 95
Discharge line temp: 133
Discharge SH: 38
Liquid Line Temp: 88
Subcooling: 7
Suction pressure: 54 lbs. (34)
Suction Line Temp: 62
Suction superheat: 28
Return Air Temperature: 72
Evap. Leaving Air Temp: 55
Evap air ∆T: 17

So? How about now?

Now - with those readings - :

-wash the condenser, and see what happens. With that much condenser, I would expect a lower head pressure.
The numbers look way better now.
Maybe that was the whole point.


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Poodle Head Mikey
08-14-2016, 09:52 PM
I love you guys - that's excellent. But I started to have a suspicion about the test gear I used so I re-did all the number just now. Of course it's cooler outside now but the various relationships should be the same.

I did go out just now and poke my head inside the unit and peek around. The condenser feed is a 3/4" copper discharge header feeding the condenser. Out of that comes a 3/4" liquid header which then drains into a 3/8" liquid line.

PHM
------



PHM,
Unless you have a subcooler, or a water cooled add on condenser , which neither would surprise me, you have a restriction in the condenser causing pre-flashing in the LL- so whatever subcooling you think you have - you dont have.


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Saturatedpsi
08-14-2016, 09:54 PM
What kind of numbers did it run (head, suction, SH & SC) before it malfunctioned?

jtrammel
08-14-2016, 10:06 PM
With that big of a condenser I'd expect a lower head pressure/temp at 88 ambient than what you have. You Got a LL drier in there somewhere?

Poodle Head Mikey
08-14-2016, 10:12 PM
I can't remember. I'm sure I must have posted them here but it's been Years ago now since I built the SOB. <g>

I can recall that I started it originally with the lowest possible SC - looking to keep the head pressure and compression ratio as low as possible.

PHM
----------




What kind of numbers did it run (head, suction, SH & SC) before it malfunctioned?

BNME8EZ
08-14-2016, 10:25 PM
Have you tried calling the manufacturer and talking to tech support.

Do you have a electronic sightglass to see how many bubbles you have before the TXV. I suppose a stethoscope might work. Considering you started with minimal SC and now you have normal to high SC if I didn't not bubbles before the TXV I would be looking at the TXV.

HVAC_Marc
08-14-2016, 11:10 PM
please tell me what's wrong -
it's busted, you need a new frankenstein unit with some other uncommon refrigerant :D

Saturatedpsi
08-14-2016, 11:21 PM
What kind of numbers did it run (head, suction, SH & SC) before it malfunctioned?


I can't remember...recall that I started it originally with the lowest possible SC - looking to keep the head pressure and compression ratio as low as possible.

PHM
----------


Considering you started with minimal SC and now you have normal to high SC if I didn't not bubbles before the TXV I would be looking at the TXV.


Since you don't remember Day 1 numbers, let's "assume" 40˚ish SST, 10˚-15˚ SH, 5˚ SC, some unknown "OD + X˚" value for the condensing temp and some unknown "approach" value.

If the metering device glitches, and underfeeds mildly, the evaporator would starve, subcooling would increase and head pressure possibly decrease a little.

Subcooling can go low with severe LL restrictions, resulting in near pump down conditions. But when I first read the OP numbers, I saw classic symptoms of some kind of mild restriction...either the TXV device or something upstream of the TXV. :.02:

heatingman
08-14-2016, 11:52 PM
Have you tried calling the manufacturer and talking to tech support.

Do you have a electronic sightglass to see how many bubbles you have before the TXV. I suppose a stethoscope might work. Considering you started with minimal SC and now you have normal to high SC if I didn't not bubbles before the TXV I would be looking at the TXV.

I thought that electronic sight glass comment was a joke, but turns out there is such a thing.

https://m.youtube.com/watch?v=xr4XYpLEMcM#


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jtrammel
08-14-2016, 11:54 PM
I thought that electronic sight glass comment was a joke, but turns out there is such a thing.

https://m.youtube.com/watch?v=xr4XYpLEMcM#


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Yea, it works pretty good too.

BNME8EZ
08-15-2016, 08:12 AM
I thought that electronic sight glass comment was a joke, but turns out there is such a thing.

https://m.youtube.com/watch?v=xr4XYpLEMcM#


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I actually even used one once, years ago, the FSR that was helping me threw one on the machine. Thought it was kinda cool but couldn't see enough need to buy one.

Poodle Head Mikey
08-15-2016, 09:54 AM
1 1/8" suction line - about 20' run - although all horizontal. And through well conditioned space.

PHM
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What is the suction line size. If low velocity and high surrounding ambients, could be gaining 5 to 8 from evap to condenser. The indoor airflow is likely higher than 600 CFM which COULD explain the low ��t

knave
08-15-2016, 05:05 PM
How can we rule out poor oil return?

Poodle Head Mikey
08-15-2016, 06:39 PM
"rule it out" ? Probably not. But I do offer up the evidence that:

1. the piping was originally sized by conservative refrigerant standards for velocity. Now granted; that was for 35,000 BTU's of R-22.

2. the suction line exit from the present evaporator is 12" lower than the horizontal suction line itself. But that 13" riser is 3/4" and has a reversed trap at the top of it - so oil cannot drain back into the cool during off cycles.

3. The 1 1/8" dead level horizontal portion of the suction line extends out to a 1/18" by 78" 90 to make the horizontal turn into the service valve. From the service valve to the compressor is 3/4" copper.

4. It is a rotary compressor which holds very little oil and would not tolerate a loss of oil for very long at all.

5. The 1 1/8" portion of the suction line has been there working effectively since the 1980's. <g>

PHM
--------





How can we rule out poor oil return?

Poodle Head Mikey
08-15-2016, 06:45 PM
Yes; it's a 3 ton R-22 TXV. I was originally going to change it to a 2 ton but Sporlan engineering told me it would turn down to about 45% - which is about 17,000 BTU's. And with the huge condenser and large evaporator that is close to what I guesstimate I get out of the system.

In case this is your question: all R-22 TXV's will control well flowing R-407C. Assuming proper application of course. <g>

PHM
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Mikey, what was that 3 ton TXV rated for? R22? since it is now R-407C inquiring minds want to know

Poodle Head Mikey
08-15-2016, 06:52 PM
I have one waiting: it's a 5 ton R-410 Carrier.

If I install a 3 ton R-410 compressor and charge the system with R-134 it will make about 17 or 18K BTU's while running very low condenser approach.

But I hate to just toss this faithful old fun system - just for some minor little misbehaving.

I haven't had any real chance to work on it - but I did do what any hackosaurus worth the license plates zip-tied onto his Sanford & Son pickup would do: I added enough refrigerant to get the head pressure to over 300, and the SSH to 18 <g> I didn't weigh it but I would guess 8-10 lbs. added.

PHM
-------



[/h]
it's busted, you need a new frankenstein unit with some other uncommon refrigerant :D

jim147
08-15-2016, 07:39 PM
I have one waiting: it's a 5 ton R-410 Carrier.

If I install a 3 ton R-410 compressor and charge the system with R-134 it will make about 17 or 18K BTU's while running very low condenser approach.

But I hate to just toss this faithful old fun system - just for some minor little misbehaving.

I haven't had any real chance to work on it - but I did do what any hackosaurus worth the license plates zip-tied onto his Sanford & Son pickup would do: I added enough refrigerant to get the head pressure to over 300, and the SSH to 18 <g> I didn't weigh it but I would guess 8-10 lbs. added.

PHM
-------

I was about to ask what 8 ounces would do but 8-10 pounds just killed my line of thought. Do you have a 30 pound receiver in that thing?

knave
08-15-2016, 07:50 PM
Why would a three ton txv need higher than 15 subcooling to maintain <15 superheat?

Poodle Head Mikey
08-15-2016, 08:03 PM
No receiver other than the condenser tubing - which is pretty big. I carried a cylinder to it which was about half full I would guess. And then I was Really surprised to find the cylinder almost empty when I put it back in the truck.

That last time I remember weighing that cylinder it was about 18 lbs. Figure maybe a 6 lb. tare and that would be about 12 lbs. of actual R-407C. And it's pretty darned light now. <g>

It doesn't matter as I have to put all the refrigerant into a reclaim cylinder in order to work on the system anyway. My thought was that maybe 350 lbs of head pressure would push more refrigerant past a possible restriction until I get to that. <g>

PHM
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I was about to ask what 8 ounces would do but 8-10 pounds just killed my line of thought. Do you have a 30 pound receiver in that thing?

Poodle Head Mikey
08-15-2016, 08:19 PM
Because it's defective? <g>

The condenser tubing is big with bigger headers. The idea that it's restricted seems unlikely to me. That leaves the LL drier (and the LL sightglass does have a tiny wiggling bubble which never quite goes away <g>) or the TXV.

I had wanted to pull the refrigerant and replace the drier before dark but I didn't make that. Now I'm thinking to do it early tomorrow.

But I have a new 1.5 to 2 TXV and a new 2 1/2 to 3 TXV sitting here in their boxes too. Justin Case. <g>

Which reminds me:

In some other recent thread we were all talking about the 'need' for LL driers. Someone stated that a clean system installed by a meticulous mechanic using the vest best methods didn't need a LL drier. Because proper evacuation would remove any moisture and obviously there would be no dirt or debris in the system.

But, IF this LL drier is clogged, it will be a case of the above kind of installation, functioning well for years, but then Still ending up with a restricted LL drier. Which was pretty much my point in that thread about why I always install a LL drier. Sometimes poop just happens. <g>

PHM
------



Why would a three ton txv need higher than 15 subcooling to maintain <15 superheat?

Cimerian
08-15-2016, 10:41 PM
I'd like to know more about how you built this system. But from what I've read I can't quite call restriction yet. I would almost say the low liquid temp is due to to much condenser airflow and the high superheat being from to large of a txv. Interesting set up you have. The restriction in the drier could be possible as poe will clean a system and put the gunk in the drier. Do you have any data as to how it was running before any issues to see what has changed?

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Snapperhead
08-15-2016, 10:49 PM
I have one waiting: it's a 5 ton R-410 Carrier.

If I install a 3 ton R-410 compressor and charge the system with R-134 it will make about 17 or 18K BTU's while running very low condenser approach.


PHM
------- So, using 134 in a 410 system loses half the Btus ....

knave
08-16-2016, 12:02 AM
I'd like to know more about how you built this system. But from what I've read I can't quite call restriction yet. I would almost say the low liquid temp is due to to much condenser airflow and the high superheat being from to large of a txv. Interesting set up you have. The restriction in the drier could be possible as poe will clean a system and put the gunk in the drier. Do you have any data as to how it was running before any issues to see what has changed?

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Hmmmm

Poodle Head Mikey
08-16-2016, 10:35 AM
Yes.

PHM
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So, using 134 in a 410 system loses half the Btus ....

Poodle Head Mikey
08-16-2016, 04:56 PM
Well; no; not exactly. "Yes" is not a complete enough answer.

The truly correct answer is that a R-410 compressor pumps half as many BTU's when it is pumping R-134. An R-410 piston will be the same size but if it's a TXV it has to have an R-134 powerhead installed on it. Each of the R-410 coils will be physically twice as large as required. But the head pressure can float down without much of an issue and so long as the evaporator airflow matches the new system's capacity - it will all play pretty nice together.

So far I have corrected two hack-job installs with that method. One was a five - now a 2.5 ton. And the other was a four - now a 2.0 ton. In a condo which really needs an 18K but I just trimmed the indoor airflow as low as I could and called it close enough.

PHM
------




So, using 134 in a 410 system loses half the Btus ....

Poodle Head Mikey
08-16-2016, 05:49 PM
OK. I finally pulled out the R-407C. The WC on the reclaim tank said 47.5 and the tank weighed exactly 47.5 after I got it all out.

I had to mildly alter the internal piping to accommodate a 163 drier (the last one was an 083) and remount the drier elsewhere as well. Two Coronas (double lime) for the evac. and then I charged it to a full sightglass.

Refrigerant: R-407C
Type of Metering Device: Fixed TXV
Ambient Temperature: 94.4
Head Pressure: 220 lbs. (99*condensing)
Condenser Air Out Temperature: 100
Liquid Line Temperature: 95.6
Liquid Subcooling: 4.4
Suction Pressure: 70 lbs. (49 evaporating)
Suction Line Temp: 67
Suction Superheat: 18
Return Air Temperature: 75
Evaporator Leaving Air Temp: 57

The reclaim tank now weighs: 36.2

I think the tare on those tanks is about 27 so the removed charge amount was about 20 lbs. I just put back about 11 lbs. I guess I could tweak the SC up to 10*to see what happens to the SSH - maybe the valve will feed more if it gets the right SC. But the original goal was to make it run as inexpensively as possible and adding SC will likely increase the head pressure and compression ratio.

And 18 at the compressor is about right - that's where I like to run Copelands.

Oh: I used all new gauges for this adventure and the thermocouples checked right on-the-money in ice water.

BTW: I checked the compressor number and found that this little LG rotary is an 18K - not a 15K as I think I wrote before.

So now what would you do?

shellkamp
08-16-2016, 06:59 PM
OK. I finally pulled out the R-407C. The WC on the reclaim tank said 47.5 and the tank weighed exactly 47.5 after I got it all out.

I had to mildly alter the internal piping to accommodate a 163 drier (the last one was an 083) and remount the drier elsewhere as well. Two Coronas (double lime) for the evac. and then I charged it to a full sightglass.

Refrigerant: R-407C
Type of Metering Device: Fixed TXV
Ambient Temperature: 94.4
Head Pressure: 220 lbs. (99*condensing)
Condenser Air Out Temperature: 100
Liquid Line Temperature: 95.6
Liquid Subcooling: 4.4
Suction Pressure: 70 lbs. (49 evaporating)
Suction Line Temp: 67
Suction Superheat: 18
Return Air Temperature: 75
Evaporator Leaving Air Temp: 57

The reclaim tank now weighs: 36.2

I think the tare on those tanks is about 27 so the removed charge amount was about 20 lbs. I just put back about 11 lbs. I guess I could tweak the SC up to 10*to see what happens to the SSH - maybe the valve will feed more if it gets the right SC. But the original goal was to make it run as inexpensively as possible and adding SC will likely increase the head pressure and compression ratio.

And 18 at the compressor is about right - that's where I like to run Copelands.

Oh: I used all new gauges for this adventure and the thermocouples checked right on-the-money in ice water.

BTW: I checked the compressor number and found that this little LG rotary is an 18K - not a 15K as I think I wrote before.

So now what would you do?
To keep the head pressure as low as possible without threatening the solid column of liquid refrigerant to the valve; you'd want to add a receiver.

Then, to achieve, as my basketball fan brother would say, "baller status" you would pipe the recieve upstream of the condenser coil's subcooling loop.

But that's an awful lot of work for almost zero gain, so if it were me I'd charge to maybe 8 degrees subcooling to give it some "cushion" when operating in lower ambient temperatures than your dealing with today.

So was your drier confirmed to be the source of your restriction?

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Poodle Head Mikey
08-16-2016, 08:47 PM
Well; the drier was the only functional part I changed today to get those readings.

The TXV holds the SSH stable at 18 so it's hard to fault it at this point.

I have been pondering just now whether to go crank the subcooling up to 10 - just to see if the SSH comes down.

BTW: I washed out the condenser and now the SC is about 8. <g>

But back to something you say here: "To keep the head pressure as low as possible without threatening the solid column of liquid refrigerant to the valve . . . . to give it some "cushion" when operating in lower ambient temperatures than your dealing with today."

Speaking of that - how about if we think of it this way: under high ambient conditions the SC is sufficient to control the SSH at a reasonable level. But if we lost the SC, and so the SSH, under low-load conditions: who cares if the unit doesn't run great then? There's less work to do then anyway. <g>

BTW: Right now it is dark, although still pretty hot outside, and the system as it is drops the temperature of the house one degree in about an hour and a half.

I would really like to reduce the air flow and get the suction pressure lower but my ducts are all way too big as it is. <g>

PHM
------



To keep the head pressure as low as possible without threatening the solid column of liquid refrigerant to the valve; you'd want to add a receiver.

Then, to achieve, as my basketball fan brother would say, "baller status" you would pipe the recieve upstream of the condenser coil's subcooling loop.

But that's an awful lot of work for almost zero gain, so if it were me I'd charge to maybe 8 degrees subcooling to give it some "cushion" when operating in lower ambient temperatures than your dealing with today.

So was your drier confirmed to be the source of your restriction?

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shellkamp
08-16-2016, 09:09 PM
Well; the drier was the only functional part I changed today to get those readings.

The TXV holds the SSH stable at 18 so it's hard to fault it at this point.

I have been pondering just now whether to go crank the subcooling up to 10 - just to see if the SSH comes down.

BTW: I washed out the condenser and now the SC is about 8.

But back to something you say here: "To keep the head pressure as low as possible without threatening the solid column of liquid refrigerant to the valve . . . . to give it some "cushion" when operating in lower ambient temperatures than your dealing with today."

Speaking of that - how about if we think of it this way: under high ambient conditions the SC is sufficient to control the SSH at a reasonable level. But if we lost the SC, and so the SSH, under low-load conditions: who cares if the unit doesn't run great then? There's less work to do then anyway.

BTW: Right now it is dark, although still pretty hot outside, and the system as it is drops the temperature of the house one degree in about an hour and a half.

I would really like to reduce the air flow and get the suction pressure lower but my ducts are all way too big as it is.

PHM
------
Well; in a "normal" system that's not throwing a hotdogs-worth of BTU's down a hallway's-worth of piping, the concern would be that a loss of subcooling, or in reality the loss of the solid column of liquid to the TXV, would cause the TXV to lose tight control of superheat and feed the evaporator unevenly.

It would probably be hard to create any real floodback to the compressor in your case. :grin:

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Poodle Head Mikey
08-16-2016, 10:07 PM
I am kind of proud of that little rotary compressor. It backspins and chatters like a SOB every time it stops and it still never misses a beat running. Other than the weird windowbox-y sound it makes it seems to be a real nice little workhorse.

Oh! and speaking of potential flood back: it has that little built-in accumulator on the side of it too. <g>

PHM
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Well; in a "normal" system that's not throwing a hotdogs-worth of BTU's down a hallway's-worth of piping, the concern would be that a loss of subcooling, or in reality the loss of the solid column of liquid to the TXV, would cause the TXV to lose tight control of superheat and feed the evaporator unevenly.

It would probably be hard to create any real floodback to the compressor in your case. :grin:

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knave
08-16-2016, 10:26 PM
I think the system is running like a top now.
I would leave it as is, maybe take the indoor blower down one speed.... it would raise your subcooling a bit. And lower the sst...

knave
08-16-2016, 11:35 PM
On second thought, you're after that low compression ratio why not just leave it....

mrkelly
08-18-2016, 06:57 PM
Your not getting enough 'head.
Read IT 'how you like.
Condenser is a lazy biotch and needs 'drug off the couch'.

shellkamp
08-19-2016, 06:32 AM
Your not getting enough 'head.

For him to be outside working on his own unit, I'd have to agree.

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Poodle Head Mikey
08-19-2016, 11:31 AM
My early evenings are often free as the little woman is at the hospital until eleven.

Someone mentioned reducing the airflow more - and he is right and that is something that I would like to do.

The problem has become that the original duct system was was designed for 1200 CFM and I am moving maybe 750. So I have a distribution issue. And the duct split off the unit has the tee in 'wrong'. It really should be side-in and it's end-in. This was fine and intentional to some extent when there was substantial air flow. But now with the small capacity and air flow it tends to starve the side-outlet end of the house.

Another issue is that the second floor system drops cold air down the stairs and into the living room. Where the thermostat for the first floor system is located. So the center of the house is cooler and the ends trend about two degrees warmer.

Fan on continuous doesn't resolve it and I dislike taking the humidity hit too.

PHM
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For him to be outside working on his own unit, I'd have to agree.

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shellkamp
08-19-2016, 11:56 AM
My early evenings are often free as the little woman is at the hospital until eleven.

Someone mentioned reducing the airflow more - and he is right and that is something that I would like to do.

The problem has become that the original duct system was was designed for 1200 CFM and I am moving maybe 750. So I have a distribution issue. And the duct split off the unit has the tee in 'wrong'. It really should be side-in and it's end-in. This was fine and intentional to some extent when there was substantial air flow. But now with the small capacity and air flow it tends to starve the side-outlet end of the house.

Another issue is that the second floor system drops cold air down the stairs and into the living room. Where the thermostat for the first floor system is located. So the center of the house is cooler and the ends trend about two degrees warmer.

Fan on continuous doesn't resolve it and I dislike taking the humidity hit too.

PHM
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Since your ducts are oversized, you can add manual dampers to balance the airflow and push more air into the starved areas. You could also change out the registers to increase the register throw and not just "dump" the air into the room.

I'd be cracking open the hart and cooley catalog to start with. Maybe just get some Opposed blade damper registers so you can balance the airflow comfortably within the conditioned space. :grin:

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Poodle Head Mikey
08-19-2016, 02:17 PM
To some extent it's like a leaking roof - when it's leaking I can't get up there to work on it and when the roof dries out enough to work on it the damned thing doesn't leak. <g>

I did close off all the 1st floor living room registers to spare the stat's reaction. But I doubt I can get the kid(s) to keep the door at the top of the stairs shut - so the 2nd floor system will always be during cold air down the stairs.

This morning I was doing something mindless and mused about the thought of maybe adding zone dampers to close off one end of the house from the other. At the main supply's first tee. But then I thought: oh yeah; I really don't give a sh!t that much right now. <g>

PHM
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Since your ducts are oversized, you can add manual dampers to balance the airflow and push more air into the starved areas. You could also change out the registers to increase the register throw and not just "dump" the air into the room.

I'd be cracking open the hart and cooley catalog to start with. Maybe just get some Opposed blade damper registers so you can balance the airflow comfortably within the conditioned space. :grin:

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