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HVAC Discussions - Heating, ventilation and air conditioning.
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Posted by Lloyd E. Sponenburgh on December 28, 2007, 2:20 pm
I just replaced the reversing valve on an old Tempstar package unit.
DAMN... the cost of the job would've half replaced the unit, but the
owner sez no. So you do the work, and only warrant that part, no?
It's a pilot-operated valve.
Anyway, what I am curious is, what is the mode of failure on these
valves? One assumption I could make is that one of the pilot lines -
almost as small as capillary tubing - has become clogged. The armature
in the pilot valve moves freely and hits both seats with authority.
If there isn't a general consensus on why these fail, I'll probably
dissect it on my own time to try and figure it out.
And no, I don't want to fix it. I just want to understand why it failed.
If they do fail from grod in the pilot lines, it seems to me it's just an
invitation for a new valve to fail in the same way.
Ideas?
LLoyd
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Posted by Bubba on December 28, 2007, 2:33 pm
On Fri, 28 Dec 2007 19:20:58 -0000, "Lloyd E. Sponenburgh"
show/hide quoted text
<lloydspinsidemindspring.com> wrote:
>I just replaced the reversing valve on an old Tempstar package unit.
>DAMN... the cost of the job would've half replaced the unit, but the
>owner sez no. So you do the work, and only warrant that part, no?
>It's a pilot-operated valve.
>Anyway, what I am curious is, what is the mode of failure on these
>valves? One assumption I could make is that one of the pilot lines -
>almost as small as capillary tubing - has become clogged. The armature
>in the pilot valve moves freely and hits both seats with authority.
>If there isn't a general consensus on why these fail, I'll probably
>dissect it on my own time to try and figure it out.
>And no, I don't want to fix it. I just want to understand why it failed.
>If they do fail from grod in the pilot lines, it seems to me it's just an
>invitation for a new valve to fail in the same way.
>Ideas?
>LLoyd
Exactly why any refrigeration system needs to have someone follow
proper brazing practices, driers, charging, evacuation and servicing.
If it were that easy, everyone would be doing it.
Bubba
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Posted by Lloyd E. Sponenburgh on December 28, 2007, 2:43 pm
show/hide quoted text
> Exactly why any refrigeration system needs to have someone follow
> proper brazing practices, driers, charging, evacuation and servicing.
> If it were that easy, everyone would be doing it.
> Bubba
I agree... sloppy, overheated, un-purged brazing seems to be the norm
in this area, and I've had to do a lot of practice on scraps to get to
the point where my joints are clean enough - inside and out - to pass
muster.
I gather you mean that chaff in the pilot lines IS the common failure
mode?
For what it's worth, though, this is a factory-sealed system - nothing
but the service ports have ever been opened. So, if soldering practice
caused the failure, it was from the factory. I guess dirt from a clumsy
topping-off might have caused it, too.
LLoyd
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Posted by Roger on December 28, 2007, 5:20 pm
I doubt plugged pilot lines are the problem - at least I've never found any.
The pilot lines see a pressure difference equal to the difference between
suction an discharge, so its tough to plug em. Given the age, I would
suspect wear or debris on the main piston/slide/shuttle , gummed-up or
damaged plastic or rubber on either the pilot or main or a plugged bleed
hole on the pilot. As to repeat failure - these things are installed in a
position so they are damn tough to just replace using all the original
fittings only without damaging the valve. I typically play it safe and add
a couple (or sometimes more) couplings as needed in a place that's
accessible and braze the valve with 50-60% silver with the valve completely
out in the open, then do the couplings with the valve installed. Also -
doing this frees you from the need to use the OEM valve - the old monsters
especially cost about the same as a compressor.
show/hide quoted text
> On Fri, 28 Dec 2007 19:20:58 -0000, "Lloyd E. Sponenburgh"
> <lloydspinsidemindspring.com> wrote:
>>I just replaced the reversing valve on an old Tempstar package unit.
>>DAMN... the cost of the job would've half replaced the unit, but the
>>owner sez no. So you do the work, and only warrant that part, no?
>>It's a pilot-operated valve.
>>Anyway, what I am curious is, what is the mode of failure on these
>>valves? One assumption I could make is that one of the pilot lines -
>>almost as small as capillary tubing - has become clogged. The armature
>>in the pilot valve moves freely and hits both seats with authority.
>>If there isn't a general consensus on why these fail, I'll probably
>>dissect it on my own time to try and figure it out.
>>And no, I don't want to fix it. I just want to understand why it failed.
>>If they do fail from grod in the pilot lines, it seems to me it's just an
>>invitation for a new valve to fail in the same way.
>>Ideas?
>>LLoyd
> Exactly why any refrigeration system needs to have someone follow
> proper brazing practices, driers, charging, evacuation and servicing.
> If it were that easy, everyone would be doing it.
> Bubba
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Posted by Bubba on December 28, 2007, 6:46 pm
wrote:
show/hide quoted text
>I doubt plugged pilot lines are the problem - at least I've never found any.
Well maybe your eye are old and you need glasses? :-)
show/hide quoted text
>The pilot lines see a pressure difference equal to the difference between
>suction an discharge, so its tough to plug em.
Never say never. It'll get you everytime
show/hide quoted text
>Given the age, I would
>suspect wear or debris on the main piston/slide/shuttle , gummed-up or
>damaged plastic or rubber on either the pilot or main or a plugged bleed
>hole on the pilot.
Didnt you just say up top that pilots dont plug?
And the op did say the piston slid freely and with authority
show/hide quoted text
> As to repeat failure - these things are installed in a
>position so they are damn tough to just replace using all the original
>fittings only without damaging the valve. I typically play it safe and add
>a couple (or sometimes more) couplings as needed in a place that's
>accessible and braze the valve with 50-60% silver with the valve completely
>out in the open, then do the couplings with the valve installed. Also -
>doing this frees you from the need to use the OEM valve - the old monsters
>especially cost about the same as a compressor.
Yup, same way I do them but I use the valve recommended. I also braze
(not solder) with the sticks, Dynaflow, Stay-silv 6 of 15 I believe
its called.
Bubba
show/hide quoted text
>> On Fri, 28 Dec 2007 19:20:58 -0000, "Lloyd E. Sponenburgh"
>> <lloydspinsidemindspring.com> wrote:
>>>I just replaced the reversing valve on an old Tempstar package unit.
>>>DAMN... the cost of the job would've half replaced the unit, but the
>>>owner sez no. So you do the work, and only warrant that part, no?
>>>It's a pilot-operated valve.
>>>Anyway, what I am curious is, what is the mode of failure on these
>>>valves? One assumption I could make is that one of the pilot lines -
>>>almost as small as capillary tubing - has become clogged. The armature
>>>in the pilot valve moves freely and hits both seats with authority.
>>>If there isn't a general consensus on why these fail, I'll probably
>>>dissect it on my own time to try and figure it out.
>>>And no, I don't want to fix it. I just want to understand why it failed.
>>>If they do fail from grod in the pilot lines, it seems to me it's just an
>>>invitation for a new valve to fail in the same way.
>>>Ideas?
>>>LLoyd
>> Exactly why any refrigeration system needs to have someone follow
>> proper brazing practices, driers, charging, evacuation and servicing.
>> If it were that easy, everyone would be doing it.
>> Bubba
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>I just replaced the reversing valve on an old Tempstar package unit.
>DAMN... the cost of the job would've half replaced the unit, but the
>owner sez no. So you do the work, and only warrant that part, no?
>It's a pilot-operated valve.
>Anyway, what I am curious is, what is the mode of failure on these
>valves? One assumption I could make is that one of the pilot lines -
>almost as small as capillary tubing - has become clogged. The armature
>in the pilot valve moves freely and hits both seats with authority.
>If there isn't a general consensus on why these fail, I'll probably
>dissect it on my own time to try and figure it out.
>And no, I don't want to fix it. I just want to understand why it failed.
>If they do fail from grod in the pilot lines, it seems to me it's just an
>invitation for a new valve to fail in the same way.
>Ideas?
>LLoyd