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Old 08-24-2011, 08:04 AM   #1
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Hello,

Yesterday we closed on the house with the missing HVAC. Went out there in the afternoon. First task was to rekey the locks ( another little hobby of mine ). Somehow, that took the whole afternoon, and then we went home.

Going out there again today to install a garage door opener. While I'm at it, I'll take out the needed tools for the HVAC job. Don't have quite everything yet, but thinking in lists I'll take out:

* Tubing bender
* tubing cutter
* O/A torch, flint starter, gas welding goggles
* Sil-Foss brazing rod
* swaging tool
* core remover tool
* charging manifold
* DMM with type K thermocouple
* Clip leads
* Fieldpiece micron gauge head
* Vacuum pump ( Robinair 15600 )
* new vacuum pump oil
* bubble level ( to mark the sheetrock for access to the linesets )
* sheetrock cutting saw ( Dremel multi-max )
* stud sensor ( to figure out where to cut the sheetrock )
* refrigerant scale ( TIF 9010, a flea market buy some years ago )
and coming from MR UPS in a few days...
* a Nitrogen purging setup.

Don't quite have the bucks at the moment to order the big equipment, but I can get ready for it. This week I figure I can:

* Open up the wall, find the linesets, cut them back to good copper
* Metalwork new copper so it terminates outside the house where the new condensers will sit. Braze it up to the old copper.
* temporarily install schrader stubs on the ends of the new copper
* flush, vacuum, leak check the linesets and the existing upstairs evaporator.
* Identify and label the thermostat wires and test the upstairs furnace with clip leads.

I'd like to install suction line filters in both systems. To have a neat installation outside the house, I figure I'll install them inside the wall with one of those little plastic access panels.

- JerryK

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Old 08-24-2011, 06:04 PM   #2
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Suction filters should be removed after 72 hours of compressor run time. So why put them inside the wall.

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Old 08-24-2011, 06:42 PM   #3
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You don't want to braze in the wall either or have the drier sweating inside a wall. Both can become bad news real fast.
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Old 08-24-2011, 07:52 PM   #4
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Quote:
Originally Posted by Marty S. View Post
You don't want to braze in the wall either or have the drier sweating inside a wall. Both can become bad news real fast.
*** I have to braze inside the wall regardless. Sweating - that's a real issue. Outside it is....
72 hours??? That's not much. That's not even one cooling season. So the filter is just a temporary stopgap to catch the crud left in the system? Once it catches the crud, why can't it just sit there? It's not like it will catch more crud - because it already caught all the crud. I don't understand...

- JerryK
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Old 08-24-2011, 07:57 PM   #5
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OK,

The 72 hours is for an activated alumina filter, which is meant to catch crud resulting from a compressor burnout. Is that the only kind there is? I'm envisioning a mere mechanical filter, to catch any bits of yuck that resulted from the system being open for a few months. There was no compressor burnout.

- JerryK
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Old 08-24-2011, 11:00 PM   #6
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I suction line drier, regardless of why it is installed, make, brand or whathaveyou, is only meant to catch any possible debri in the lineset, stopping it from making it into the compressor. Regardless of burnout or not they are meant to be removed. The high pressure line drier aka liquid line drier is permanent.

Now if you are installing a heat pump than you have to still remove the suction line drier after ONLY running it in cool (so the refrigerant flows only one way in vapor form back to the compressor, normal cooling flow, thus catching all possible debri in the suction line drier) but you must install a bi-directional liquid line drier as a bi-directional will not blow back any trash once the refrigerant reverses flow, for heating.

Not uncommon to see suction line driers left on systems without any trash in them for a decade, it's just not how they're meant to be left.
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Old 08-25-2011, 05:13 AM   #7
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A suction filter reduces system capacity when it has a 3 PSIG pressure drop across it. And it does take long for that to happen.

While I've seen more then one suction filter that has been on a system more then 5 years not restrict. I've seen plenty that restricted in 1 day.

72 hours of compressor run time is lot of refrigerant circulation. Roughly 180 pounds of refrigerant an hour per ton. So a 3 ton system will have moved roughly 38,880 pounds of refrigerant through the filter drier in 72 hours of compressor run time.
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Old 08-25-2011, 05:46 AM   #8
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I am not familiar with the suction line filters. I assume you'd have to pump the system down to remove it.... or can you install them in a separate line branch in parallel with the regular vapor line that can valved in and out?

Also, with a condenser unit that comes with a built in filter/drier, do you guys recommend still adding an external filter/drier? Are the OEM ones good enough? If not, would having another filter/drier in series create too much restriction?
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Old 08-25-2011, 05:55 AM   #9
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Best not to install a second LLFD on a new unit.

No, suction filters can't be installed in a second parallel line, they wouldn't be able to do any real filtering.
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Old 08-25-2011, 06:17 AM   #10
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I meant valving one line in and the other off totally. I guess that would complicate the install.

Thanks for the input on the LLFD.

BTW, you get up too early. But so do I!



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Best not to install a second LLFD on a new unit.

No, suction filters can't be installed in a second parallel line, they wouldn't be able to do any real filtering.
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Old 08-25-2011, 07:04 AM   #11
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As long as there is no pressure drop between the suction filter and the compressor you can leave it in line forever.

However i would never install one where I couldn't get to it for a change out.

Last edited by COLDIRON; 08-25-2011 at 07:06 AM. Reason: added text
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Old 08-25-2011, 02:09 PM   #12
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Quote:
Originally Posted by COLDIRON View Post
As long as there is no pressure drop between the suction filter and the compressor you can leave it in line forever.

However i would never install one where I couldn't get to it for a change out.
Problem is, you n ever know when it will restrict down the road.
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Old 08-25-2011, 05:47 PM   #13
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Problem is, you n ever know when it will restrict down the road.
*** Why would it? Does the system generate crud out of nothing? If the system does somehow generate crud out of nothing, wouldn't it be better to have it clog up a filter than grind up the compressor and/or foul the TXV?

My new invention: the crud sensor. Consists of a pressure switch across the filter.

- JerryK
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Old 08-25-2011, 05:51 PM   #14
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Quote:
Originally Posted by beenthere View Post
A suction filter reduces system capacity when it has a 3 PSIG pressure drop across it. And it does take long for that to happen.

While I've seen more then one suction filter that has been on a system more then 5 years not restrict. I've seen plenty that restricted in 1 day.

72 hours of compressor run time is lot of refrigerant circulation. Roughly 180 pounds of refrigerant an hour per ton. So a 3 ton system will have moved roughly 38,880 pounds of refrigerant through the filter drier in 72 hours of compressor run time.
*** No, it moves 5 pounds of refrigerant through the filter 7776 times. Kind of like a small country trying to impress by marching the same troops past the bandstand and around the back.

- JerryK
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Old 08-25-2011, 06:24 PM   #15
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Quote:
Originally Posted by jerryk1234 View Post
*** Why would it? Does the system generate crud out of nothing? If the system does somehow generate crud out of nothing, wouldn't it be better to have it clog up a filter than grind up the compressor and/or foul the TXV?

My new invention: the crud sensor. Consists of a pressure switch across the filter.

- JerryK
oil can break down. And does at times, and will clog the filter. A restricted suction filter drier drops system capacity, and causes the compressor to run hot. You don't notice the loss of capacity right away, but the compressor notices it.

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