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Split system - when to replace


MPdesign
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Hello gents,

I typically call for replacement of a pad mounted heat pump or condensing unit every 15 years - but I do not call for replacement of interior fan coil unit.

Should I be calling for the replacement of the interior fan coil unit also - because of energy efficiency interactions?

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At that age I simple say it's nearing it's end of the "typical life span" of said unit. I tell folks they shouldn't be surprized if it breaks in an hour or two. If it's still working well, I see no need to call for a replacement. If it ain't broke.....

If I understand correctly, the modern systems are "supposed" to be matched (inside and out) and it's not a good idea to only replace one of the two.

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Hello gents,

I typically call for replacement of a pad mounted heat pump or condensing unit every 15 years - but I do not call for replacement of interior fan coil unit.

Should I be calling for the replacement of the interior fan coil unit also - because of energy efficiency interactions?

Yes, a large part of the effiency ratings of the newer units is due to the variable speed fans.

Also, the newer units will be using R-410a. It can be difficult to thoroughly clean the old coil to remove all traces of the R-22 oil, which isn't the least bit compatible with R-410a.

- Jim Katen, Oregon

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R-22 units use mineral oil.

15 year life on heat pump/condenser units? No. I've known some to last 12 years, others still in service and functioning well after 30 years.

It would be nice to have a number like that to know how many years of service are left but it's folly.

Marc

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If the unit is being removed 'properly', the RMS machine is attached and is programed to recover. During recovery all of the oil is also sucked out as well, mostly. It wont clean out the dryer so replace that and accumulator, depending on set up. Once all the changeover is complete a 'deep vacuum' (30 inches) for 30 minutes is required to clean out the system. Deep vacuum gets pretty much everything out except metal filings. Recharge with new R and PAG. Hope that the old parts (evap, txv,et al) continue to hold.

Personaly, I would change my sytem complete, but thats me.

Hello gents,

I typically call for replacement of a pad mounted heat pump or condensing unit every 15 years - but I do not call for replacement of interior fan coil unit.

Should I be calling for the replacement of the interior fan coil unit also - because of energy efficiency interactions?

Yes, a large part of the effiency ratings of the newer units is due to the variable speed fans.

Also, the newer units will be using R-410a. It can be difficult to thoroughly clean the old coil to remove all traces of the R-22 oil, which isn't the least bit compatible with R-410a.

- Jim Katen, Oregon

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If the unit is being removed 'properly', the RMS machine is attached and is programed to recover. During recovery all of the oil is also sucked out as well, mostly. It wont clean out the dryer so replace that and accumulator, depending on set up. Once all the changeover is complete a 'deep vacuum' (30 inches) for 30 minutes is required to clean out the system. Deep vacuum gets pretty much everything out except metal filings. Recharge with new R and PAG. Hope that the old parts (evap, txv,et al) continue to hold.

Personaly, I would change my sytem complete, but thats me.

Mongo, refrigerant recovery units do not recover oil, which remains in liquid form even under deep vacuum conditions. In fact, refrigerant and any other gases (air, nitrogen, other noncondensibles) are the only things removed by them. Deep vacuum doesn't clean out the system at all.

I personally agree with you on changing the entire system.

Marc

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The reason for a "deep" vacuum is to remove moisture as it will boil off.

The only way to really cleanse a system is with a refrigerant like R-11 which has cleansing proprieties, like dry cleaning fluid (was also used in large tonnage centrifugals). However was the first on the chopping block due to the Montreal Protocol.

A suction line dryer will help clean up a system, like after a motor burn, however it won't clean a R-22 system that will be switched over to R-410a.

Also, as Marc has stated, a recovery machine will only remove refrigerant.

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I have read just now on a few sites about the increased pressure. Is there any problem with the pressure in the old coils that could cause rupture because of a thinner wall?

On the oil... I have just seen a few sites that mention draining the oil, adding new oil, putting the reclaimed r-22 back in - running for a while, removing the R22, checking oil properties with a test, and repeating until the % of old oil is tolerable then changing nameplate data. That is typically for different types of replacement refrigerant from R410 though.

What do you guys think about these issues?

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Hey Marc, they use a smaller machine than mine.

The RMS recovers everything in the system, including all the oil. Deep vacuum, as stated, creates a deep vacuum inside (approx 30in mercury), the reason for this is to lower the boiling point of the fluid. The oil boils off and is collected in the machine. Some of the machines that the AC guys use will not recover the oil, they are for installs only. My background is Military and Industrial Cooling and Heating (amongst other mech trades), all portable but large systems. When we have to break it down the RMS machine comes out, Pressure Testing, Evacuating, Recovery, Deep Vac and Charge System and replace the oil all in one.

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I have read just now on a few sites about the increased pressure. Is there any problem with the pressure in the old coils that could cause rupture because of a thinner wall?

On the oil... I have just seen a few sites that mention draining the oil, adding new oil, putting the reclaimed r-22 back in - running for a while, removing the R22, checking oil properties with a test, and repeating until the % of old oil is tolerable then changing nameplate data. That is typically for different types of replacement refrigerant from R410 though.

What do you guys think about these issues?

Change the evap coil, period, unless you're a refrigeration engineer.

As for this procedure for removing traces of mineral oil by repeated dilution with a synthetic oil that is compatible with R 410A, the miscibility of mineral and synthetic oils is zero, so the dilution theory is mistaken. Do you dilute oil with water?

This synthetic oil is very nasty. It should not be permitted to touch your skin. Mineral oil, used in R-22 systems, is a common ingredient in skin ointments and medicines.

Marc

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Hey Marc, they use a smaller machine than mine.

The RMS recovers everything in the system, including all the oil. Deep vacuum, as stated, creates a deep vacuum inside (approx 30in mercury), the reason for this is to lower the boiling point of the fluid. The oil boils off and is collected in the machine.

Refrigeration oil does not boil at 30" of mercury (however water does). Techs routinely pull this amount vacuum but never have to refill a system with refrigeration oil after the fact. Pulling a "deep vacuum" will NOT remove all traces of refrigeration oil!

I've worked on many a system, pulling a 29.9" vacuum and never had to replace compressor oil. We use to drain the oil on large ton systems, using a pump designed to evacuate liquids, but a vacuum pump ain't sucking all the oil out of a system.

Having been out of the industry for a number of years though perhaps they have come up with a vacuum pump that is not only used for the evacuation of vapor but will also convert into a liquid pump. Can you point me to a web site that sells such a product? God knows I've been wrong before.

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As for this procedure for removing traces of mineral oil by repeated dilution with a synthetic oil that is compatible with R 410A, the miscibility of mineral and synthetic oils is zero, so the dilution theory is mistaken. Do you dilute oil with water?

This synthetic oil is very nasty. It should not be permitted to touch your skin. Mineral oil, used in R-22 systems, is a common ingredient in skin ointments and medicines.

Marc

As I said, that was not for R410A - it was for other refrigerants such as R427A. I saw no such reference for R410A - but that is why I asked.

Thanks for the clarification.

So the coils will hold the pressure?

I know that I am being the devils advocate here but I like to have all of the details and make my own informed decisions on a case by case basis because there are a lot of very different cases out there.

PS. Love the Mongo... Soo Cool.[:-thumbu]

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I have read just now on a few sites about the increased pressure. Is there any problem with the pressure in the old coils that could cause rupture because of a thinner wall?

On the oil... I have just seen a few sites that mention draining the oil, adding new oil, putting the reclaimed r-22 back in - running for a while, removing the R22, checking oil properties with a test, and repeating until the % of old oil is tolerable then changing nameplate data. That is typically for different types of replacement refrigerant from R410 though.

What do you guys think about these issues?

Ok....

If you're converting from a 22 to a 410 system, and don't want any problems, replace everything - condensing unit, line set and evaporator. The only person I would trust to properly clean the system of all traces of the old refrigeration oil would be me. There are as many hack A/C contractors as there are roofing companies. Quick, short, cut corners, get in and get out philosophy prevails. People flock to low bid and you get what you pay for.

Marc and I got into a discussion about liquid line dryers a while back and their necessity. To boil it down - you buy a new, pre-charged condensing unit, an evaporator that has a holding charge of nitrogen and an ACR line set that is virgin with a nitrogen holding charge. As you braze the copper you purge with nitrogen to prevent contaminants/flakes. Pull a proper vacuum then test. If everything checks out you open the services valves to let the refrigerant out of the condensing unit. Start, check and adjust charge as need to compensate for length of run.

Are liquid line dryers needed? No. Are the necessary? Absolutely. There are a lot of techs that cut corners and/or are not taught properly.

So much mis-information out there. Let's stop posting to every post because we like to see our name in lights. Let's post when we are sure that we passing on solid information that our fellow inspectors can pass onto our clients.

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Terry, This is a photo of my recovery unit. Bought it about 10 years ago. Look at the blue dial and the setting that says 'liquid'. Now, I don't think that there is a pump installed, rather it's just an orifice or heat source that boils the incoming liquid refrigerant so that only gaseous refrigerant enters the compressor. I could be wrong.

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Marc

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Terry, This is a photo of my recovery unit. Bought it about 10 years ago. Look at the blue dial and the setting that says 'liquid'. Now, I don't think that there is a pump installed, rather it's just an orifice or heat source that boils the incoming liquid refrigerant so that only gaseous refrigerant enters the compressor. I could be wrong.

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Marc

That's for refrigerant, not oil, however I understand your point. The Robinair recovery machines we used had a liquid switch to so that you could tap the liquid line thereby evacuating the system quicker. The point is you wouldn't use a recovery machine to pull a vacuum and a recovery machine, as well as a vacuum pump, does not remove compressor oil.

A recovery machine and a vacuum pump are two different animals.

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Hey Marc, they use a smaller machine than mine.

The RMS recovers everything in the system, including all the oil. Deep vacuum, as stated, creates a deep vacuum inside (approx 30in mercury), the reason for this is to lower the boiling point of the fluid. The oil boils off and is collected in the machine. Some of the machines that the AC guys use will not recover the oil, they are for installs only. My background is Military and Industrial Cooling and Heating (amongst other mech trades), all portable but large systems. When we have to break it down the RMS machine comes out, Pressure Testing, Evacuating, Recovery, Deep Vac and Charge System and replace the oil all in one.

To expand on this a bit - and I'm not trying to be argumentative.

Seeing as oil will not boil at 29.9" of vacuum how does this system remove all the oil?

Let's, for a moment, assume that it does. Does it remove all traces from the inside of all surfaces? Does the machine store the oil in a separate container so that it can be measured/weighed out? If you're working on a system, and you've just removed all the oil, you will need to know how much to add back in (assuming that it is a hermetic compressor with no sight glass).

I can recall watching a sight glass, for oil level on a semi-hermetic compressor, and seeing it bubble as a vacuum was pulled but this was only refrigerant boiling off from the oil. This is why we shouldn't run recip compressors when it is cold outside. The refrigerant migrates with the oil and will be pumped out - and as we all know you can not compress a liquid - something will break.

In my former life we use to work on systems that were 1,000 tons plus. I'm most comfortable in big commercial/industrial equipment rooms. I've designed custom control systems (Barber-Coleman Controls) for oil chillers on gear cutting machines - Horsburg & Scott. Went through trade school from 1977-1979. Did the hands on work till a fall ruptured three disks in the neck. Had spine surgery in 1984 and then went into management for the rest of my HVAC career which consisted of Service Manger, Service Sales, Sales Manager and General Manger. Responsible for a 7 million dollar service department which included supervision of 32 union pipe fitters, 5 union plumbers, GPL as well as a on going 5 year strategic plan.

Also worked with the Cleveland School System in the maintenance department - lot's of exposure to fire and water tube boiler systems.

I've never felt compelled to post a resume before but, for some strange reason, feel the need now.

Having been away from the industry for many a year perhaps the technology has past me by (wouldn't be the first time). I'm always willing to listen.

Sorry to go a bit sideways with this thread...

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Mongo may have been referring to non-hermetic units where the compressor can be dismantled and repaired. These are commercial grade units that the military may have been using. Some have a port above the crankcase where you can insert a tube and suck out the oil.

Marc

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Mongo may have been referring to non-hermetic units where the compressor can be dismantled and repaired. Marc

You mean a semi-hermetic compressor? A vacuum pump will still not remove compressor oil.

These are commercial grade units that the military may have been using. Some have a port above the crankcase where you can insert a tube and suck out the oil.

With a vacuum pump?

EDIT: Changed because I was being an a-hole - as usually.

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Terry may be an asshole(Said with nothing but the utmost respect), but he's absolutely correct in this thread.

Sure, you may get lucky and get a system to work by mismatching condensers and coils and line-sets, but why risk it? If someone's going to replace a condenser, why not spend an extra fifteen-hundred or so and buy a whole new system and the warranty that comes with it? Why risk damaging the condenser by hoping you sucked/cajoled/conjured the old oil out of the system?

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Hey guys,

When I related the vacuum pump to pulling in the oil and other contaminates from the system, I should have added that the compressor simply cannot give it up. But the lines will have residue that is pulled by vacuum during evacuation. Most of our compressors have a drain and fill port. Never saw a dipstick on one, we used cable ties and dipped it in through the fill port.

As for welding or soldering up a contained system, never. That sounds more like a house unit or a fridge. All the units I worked on where either vehicle mounted, in a medium box, in a sea container (field hospitals) driven by the engine or electical motors.

I too have been off the floor for a bit, so, mea culpa's to all.

I will be more specific in my posts.

mongo

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To support my stance on oil recovery, I direct you to the Robinair website for the model 34700Z. I have not used that particular model but it also removes oil.

The 34700Z is equipped with automatic oil drain. During the recovery process the air conditioning system oil is collected and drained into a bottle built into the unit. Robinair AC machines are also great for recharging your air conditioning system.

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Now this is the type of discussion that I was hoping for. If nothing else, you gentleman are educating lowly engineers (like me) all of the world on the issues at hand. I do not see where anyone is being impolite.

I was hoping that someone would look up the specs on their equipment. I do suspect that it is good for some types of refrigerants such as R427A but not necessarily for R410. Some refrigerants only require 95% pure new oil and they are fine. Apparently R410 is not fine with any residual oil.

Once again though, I am just an engineer. I defer to the experts who have real field experience.

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Which discipline of engineering would that be?

My Sporlan Pressure/Temperature chart doesn't show an R-427. It's an old chart, perhaps 427 is a new refrigerant. I haven't been active in refrigeration for 6 years. Which manufacturer is it that is using this refrigerant?

Marc

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