HVAC System - Hack Job?

[Cynthia]

A few years ago, I had my HVAC system replaced and recall they did a really good job measuring, matching the new indoor and outdoor units, and installing everything.

A friend of mine is buying a house with a heat pump. The sellers bought a new outdoor unit, but *left the original old indoor unit intact.* But it gets more interesting, the new unit is a Carrier "Weather Maker," model 38YXA024330 and says "Puron."

How can an outdoor unit made for Puron work with an old R22 indoor unit?

The indoor unit is a Synder General model BYMBO024 (no joke that's actually the model number).

Will this setup work at all? Is there even a warranty on such a system if the indoor unit isn't replaced? How do you measure efficiency on such a system?

Thanks!

[trader4]

At significantly reduced efficiency, and that's if they are luck? My understanding is the same as yours which is that coils that are in a system that used R22 are incompatible with R410A. Not only are there performance differences, but R410A systems operate at significantly higher pressures than R22, so the coils are built and tested to withstand those higher pressures. The oils used are incompatible so the old system would have to be completely flushed of all the old oil. You have to wonder what else a hack that would do this would skip.

Warranty by whom? The manufacturer of the new unit? No way. By the hack who did the job? Possibly, but good luck getting them to honor it.

This is a good example of what NOT to do. The sales contract should have had a clause giving the buyer the option of negotiating a discount off the sales price instead of having the seller make the repair. That way the buyer could have decided what to do and that probably would have been to replace the whole system with one of their choosing, letting them decide the cost vs efficiency, etc. Doing it the way it was done here, the seller is just going to do whatever they can for the cheapest price to get it working again. Also, in many areas there are utility or state rebates for higher efficiency systems that can give you a better system for a little more money. Those rebates sure don't apply to half a system.

As the buyer, they should get the system inspected again by a reputable contractor of their chosing. Hopefully they can get a written opinion that it's a hack job and then demand the above discount from the selling price.

[jamesgangnc]

Depends on exactly what left the indoor unit intact means. You can simply replace the A coil on the inside unit and leave the rest alone and that would be fine.

As to making the original A coil work with the new r410a outside unit there's some controversy there. A lot of people argue against that. However on the other side of that issue Goodman sells cased A coils that are the same and are used for both their r22 and r410a systems. And it is common for a single A coil to match a range of outdoor units by just changing the orifice or txv.

All that happens in the A coil is the release of the high pressure liquid refrigerant to a larger area where it returns to being a gas. And it is circulated through the tubes to pick up heat from the inside air passing over them.

Some people install an oversized A coil to try to increase efficency. The more time the lower temp refrigerant is exposed to the higher temp insode air the more heat it picks up. One of the biggest noticable changes in the outside units as they increased efficiency is the same thing, larger coils. Just compare any newer unit to an older one. They are all bigger for the same tonnage.

However, knowing what the results of these mismatches are statistically is anyone's guess. That's the main arguement against. If you install a complete sytem then you have something that was tested as a unit in a lab somewhere.

[RicodJour]

Regardless of their age it's still negligence. You're making excuses for old guys - how old are you again...? :)~

R

[Colbyt]

Be sure to read James post. All that need be changed is the A-coil. The rest of the old unit should function fine.

[Home Guy]

What else is there when it comes to the "indoor unit" other than the A-frame coil?

[JimT]

I would think it would be difficult using anything other than what the unit is designed to hold.

[trader4]

Since it's not a furnace, I guess basicly it's the air handler. You could probably find an R410A coil compatible with the outdoor unit. But if you look at pricing the whole thing, it would probably make more sense to have just replaced the entire system because it's probably not a lot more for the whole thing. It also depends on the age of what's there, any utility rebates that you could get on a complete system versus just changing part of it, etc.

But again this is a good example of why when buying a property you want a credit for things the inspector finds instead of having the seller fix it. That way you can decide what's best based on your criteria and situation. We know what the seller's criteria is. Fix it as cheap as possible to get it working.

Another point. It's not clear if this repair was the result of a home inspection or not. If it was, one obvious thing to do is ask the home inspector what he thinks about how it was done. May not be too productive, as most of them just say "this ain't working, needs to be evaluated by an HVAC guy", but it can't hurt to ask.

[Home Guy]

Nuts. Totally nuts.

You purge all old refridgerant, connect the lines, throttle the compound gauge?s regulator and the refrigerant cylinder?s regulator to purge again. Pressurize the system to a point just below the condensing pressure, turn the unit on, add refrigerant until the pressure in the low pressure side reaches the design operating pressure, check the superheat, and make sure that the sight glass is clear.

[JimT]

The comment was regarding changing the A-frame coil not purging the unit.

[Colbyt]

I suppose in some places the indoor part is just an air handler. Here back up heat strips are required so you have those, the controls, the air handler part.

Why replace all of that if the proper coil will fit in the old shell?

I just replaced my unit here this year. I sure did not buy a new furnace. We just replaced the A-coil and the condenser unit.

The average homeowner looks at the old shell and does not see the new coil inside the unit so they think nothing was done inside.

[trader4]

If it's 20 years old and you can get a whole new unit for a few hundred dollars more, that would be a good reason.

And if rebates are available from the local utilites, govt, etc, in most cases they are going to require that the whole thing be replaced. That's because the system has to be certified by the manufacturer to meet certain efficiency standards to qualify. Factor that in, plus any rebates from the manufacturer, etc and the cost of a whole new heat pump system versus replacing just the outside unit and the coil could be small.

He doesn't have a furnace so the cost difference of replacing the whole unit isn't going to be as much.

That's a good point. It's possible that's what happened in this case. We don't know on what basis they concluded that only the outside unit was changed.

[Home Guy]

Why replace the coil in the first place?

It's got no moving parts!

What's the total cost (including labor) to rip out the old coil and replace with new?

What is the actual, practical benefit of doing that?

If it ain't broke, don't fix it.

The coil has no moving parts. Fer christ sakes, you might as well say that the copper lines running between the air handler and outside unit should be replaced while your at it. Because new lines are always better than old lines - right?

[trader4]

Sounds like you've never seen one rusted and falling apart. As for reasons, I just gave a list.

It's not just the coil. It's the coil plus the outside unit that we are talkiing about in this case. That's the cost that should be compared to replacing the whole heat pump system. And as I stated, factor in any rebates from the manufacturer, utilities, tax incentives, etc. Those almost always apply only to COMPLETE SYSTEMS. I think when you do that for a heat pump system, it's not much more for a whole new system which is then brand new and has a long warranty on everything.

Already listed the practical benefits.

So, you're OK with putting an R410A outside unit on an old R22 system regardless of the age or how little it might actually cost to replace the whole thing?

I replaced my system recently and used new lines. For $200 and given they were 27 years old, passing through concrete blocks where they can't be inspected, I think it was the right thing to do. Three of the contractors who quoted the job were of the same opinion. One, the low bidder, wanted to re-use the existing lines.

[The Daring Dufas]

That sounds like the name of the furnace/air handler. The new coil could be sitting on top of the old furnace which shouldn't be a problem if the air handler is working and has adequate air flow. Check to see if there is a new A-coil atop the old furnace,

TDD

[The Daring Dufas]

A-frame coil? *giggles* Sorry, HVAC is one of the things I do for a living. :-)

TDD

[The Daring Dufas]

We have changed out systems and converted the old gas furnace to emergency heat for the new heat pump. There is a control mod on the market to do just that. The pressures for the new R410a refrigerant are much higher than the old R22 systems so it's not likely anyone will try to reuse an evaporator coil but the line set could be OK. I would flush the line with nitrogen and internal system cleaner if I reused it to get rid of any mineral oil and contamination. As long as the old air handler produces acceptable CFM for the R410a evaporator, there is no reason to have to replace it unless it's worn out.

TDD