Diagnosing reversing valve vs scroll compressor?

[Larry2]

One of my heat pumps died during recent sub-freezing weather. It's a system that manages an unused room, so it is typically set to a very low temperature during winter. The system worked quite well and then failed during this cold weather snap.

This heat pump uses a copeland ZR18K3 scroll compressor.

I connected my gauges and started the system after the compressor had cooled for the thermal reset. I pushed the contactor in by hand while watching the gauges. The suction and discharge pressures didn't change any as the compressor started and ran. The compressor makes the typical sounds that change during the first five or ten seconds of operation. If you were to hear the unit as it started up, you would think it was perfect.

I cycled it between cooling mode and heat mode, hoping to free up the reversing valve so this could be attended to during nicer weather. But of course with no pressure differential to work the shuttle, I'm not sure this would do anything useful. Hope springs eternal.

The compressor shuts off on the internal thermal switch, perhaps after twenty or thirty seconds of running.

The discharge port didn't get warm and the suction port didn't get cold. With no refrigerant flowing, it's not surprising the thermal switch cycled of.

Short of swapping the compressor or the valve in trial and error, is there any diagnostic test I can do to sort out if the reversing valve is shuttled between modes?

My hunch is the compressor is bad. It's almost like the scroll is disconnected from the motor. Can that happen? Does anyone have ideas?

[The Viking]

Ideas?
No, sorry.

But....

Normally when the reversing valve get stuck, you would find the discharge and suction lines getting hotter and hotter until the clixon drop the compressor out.

Now you are saying that the discharge and suction lines are staying cool...
Well, as something must drop the clixon, you either get a high temperature inside the compressor OR it is pulling a high current...(would be interesting to know what current it's pulling)

So,
With the limited data we got and the fact that the pipes stays cold, I would say the compressor had it.

(If this is a 3-phase machine, there isn't a chance that the phases has been reversed?)

[nike123]

If your compressor doesn't turning in reverse direction, then it is compressor fault, because you should have hot discharge tube with valid compressor.
Do you have Rotalocks on compressor?
If you use air to water heat pump in extra low temperatures conditions possibility is that you heaved liquid floodback and that is broken compressor valves.
Does someone charged refrigerant before?

[Larry2]

This heat pump is an air to air unit. The charge has not been tinkered with since it was installed in 1993. The room it serves is seldom occupied, so the compressor has comparatively few running hours for it's age.

The compressor is brazed in. I think it relies on the scroll rather than valves since it doesn't have a reciprocating motion. The scroll is supposed to be tolerant of liquid flooding. It is supposed to safely raise off the seal during a floodback situation, if I understand the literature correctly. Still, I have a question about that. The compressor lacks a case heater. The Copeland literature says one isn't necessary because it can tolerate momentary flooding. Is this strictly so?

The air handler is located one story above the outdoor unit. This unit is usually set to low temperatures during heating and higher temperatures during cooling season because the room isn't occupied. It might sit many hours or days without running.

This has a single phase scroll compressor with a run capacitor. It wouldn't be possible for a single phase motor to run backwards, would it? I've read they can run backwards if a momentary power glitch allows power to return the instant is spins backwards from stopping. This unit has a short-cycle timer, so that shouldn't be possible.

The unit was running okay until it ceased heating during the severe weather. It is almost as though running a defrost cycle caused a failure. This weather might have been the first time this heating season that it called for defrosting. I checked it with gauges last season during warm weather and subcooling was satisfactory.

[The Viking]

OK,
The defrost cycle might have caused the compressor failure.
But if the pipes doesn't change temperature, the compressor is a goner...

The reversing valve might also be gone, but that's hard to prove/disprove without a working compressor.

[chris96]

Another possibility is that the check valve has stuck, i had this on a heat pump once, it caused poor pressures/temps and in the end the compressor packed up from liquid return when heating.
I must admit tho i had a bit of heat on the discharge pipe.
I also thought it was the reverse valve at first.
This was on a mitsi mshga60vb

[Larry2]

But if the pipes doesn't change temperature, the compressor is a goner...

That was my notion too. I'm trying to understand what can go bad in a compressor that has so few moving parts that would let it spin but not produce any suction at all.

Is there any kind of shear pin that can disconnect the scroll section from the motor?

[The Viking]

There are a multitude of options...


(Worn valves)



(Ruptured discharge pipe)



(Rubbish blocking vital parts)

Sorry, can't seem to get the piccies in, you have to look at the attachments.



I also have a picture of a scroll plate where all the "ridges" has disappeared but I can't find it at the moment.

[Chunk]

Hi try this link http://www.emersonclimate.com/contractor/support there is a lot of usefull info on scrolls. Chunk.

[powell]

Larry2,

Here's a couple links that might help.

Scroll Troubleshooting: http://www.hvacrinfo.com/scroll_trouble.htm


Copeland AE bulletin: http://www.hvacrinfo.com/cope_ae_bulletins/TAE1312.PDF

[Larry2]

Viking, thanks for the photos. Chuck, thanks for the link. I read what I could find online concerning scroll compressors last year but the information I find now with your help is much more comprehensive. Many of the links were dead last time I looked. In one documents Emerson shows and explains scroll breakage from floodback. This is in conflict with what I read earlier that said they were "tolerant".

http://http://www.emersonclimate.com...odedstart.shtm

Breakage like they show from floodback would certainly explain lack of any pressure change on startup even though the motor is spinning.

I found an engineering application bulletin giving guidance concerning floodback and oil management.

http://www.hvacrinfo.com/cope_ae_bulletins/TAE1312.PDF

I don't believe my system was overcharged. It has never been topped off since 1993 when it was installed. The unit lacks a crankcase heater. The notes suggest one isn't always needed, but 10*F is in the danger part of their graph and I'm sure the unit cold soaked to that temperature the night it failed. The lineset, which might be 50 foot (16 meteres) runs through the unheated floor beneath the space. The underside of that floor is an unheated garage. The system is badly oversized for the job, so it short cycles. We don't use this space, so we maintain it at 55F (12C) when it's unoccupied during the winter and similarly warmer than comfortable during the summer. The night if failed was 10F (-12C), maybe less.

The contractor who designed the system specified a 19,000 btu/hr system to condition two well insulated rooms with a combined area of 700 square feet. Needless to say the unit is excessive and in moderate weather the system quickly satisfies the thermostat. I asked for a mini-split at the time, but he had never installed one and he wasn't willing to consider it. When questioned about the size of this unit, he said this unit was the smallest SEER 13 on the market. He made a lot of mistakes both on this system and the other two. I should have have paid more attention.

The engineering bulletin says it is critical for the minimum run time to be long enough for oil to return to the compressor after startup. I think this unit has spent a lot of it's life running five minutes or less at a time.

I can replace the compressor; I already have a new replacement. I can add a crankcase heater. I can change the heat anticipator so it runs a bit longer. What other steps can I take so the new compressor is treated better? Would an accumulator we worth the trouble on this unit? The application note doesn't really call for one on this small a unit. I forgot to mention, this system have txv for both heating and cooling cycles.

[The Viking]

Larry,

It's 15 years old.
It's running on a gas that is getting phased out.
It's had a compressor failure, which in turn might have contaminated the system.

A new unit would be sized for your requirements.
A new unit would be more energy efficient (if you choose it to be).

Your old unit has served it's time, let it go to the big air-conditioned space in the sky.

(My recommendation would be a small inverter driven system, operating on R410A)

[powell]

Larry2,

You have a system that ran good for 15 years with no servicing required except for general maintenance (I assume), then a compressor failure. This tells me that you have had a component failure or something has changed in the dynamics of the original system design: ductwork, supply or return grilles, piping, etc.

If it ran 15 yrs w/o a cchtr and an accumulator then you shouldn't need one now. I will say though, accumulators are quite popular on heat pumps.

After the compressor has been changed, use the good advice of the comments on this thread and the links provided and you will find the demon that killed this compressor.

[p_p]

I'm with the Viking. Time to replace it .

[Larry2]

This an old topic that I'm bumping to the top. I have decided to replace the outdoor section with all the great advice here. Actually, I will replace all three systems here through the season. This is the only one I plan to mismatch air handler and outdoor sections.

I intend to keep the existing air handler, coil, txv and pipework. If I have an issue on heating mode pressures, I'll swap the air handler and coil assembly later on. I have cut the old unit away ready for salvage and I'm prepared the new pad for mounting. That landscaping correction is worse than the rest of the job.

The oil doesn't smell burned or toxic. It continues to drip oil from the air handler above, even though the system was shut down months ago. I guess I caused some of that oil to flow myself, from flowing dry nitrogen through while connecting new pipework. Still, it seems like there was too much oil in the evaporator.

My concern now is to identify the original cause of the system failure so it doesn't happen again. This system didn't fail from wear-out. It failed catastrophically during cold weather. I'm thinking it was slugged with liquid stored in the cold pipe work or cold compressor crank case. The pipework ran through a cold garage ceiling while the outdoor system was at 10 degrees F when it failed. It might have failed during a defrost cycle for all I know.

I have cut open some brazed joints near the unit, and sure enough they were brazed with benefit of nitrogen flow. That workmanship looks nice. I haven't cut open the compressor to see what went wrong inside yet. It is not a burnt out though, since it spins freely under power.

How effective is a non-bleed txv for preventing refrigerant migration? Would it be a fair trade-off to buy the txv repair part matching the Rheem coil and install it even if it doesn't have an equalization port like the original has?

Or should I install a liquid line solenoid valve instead?

I plan to add the crankcase heater. That seems to have the highest return for dollars spent. I will change the thermostat to a new digital design that limits cycles per hour to correct short-cycling.

[Brian_UK]

Since it will be properly commissioned with a genuine hastings vacuum gauge overnight, there won't be leaking or impact from this system.

I plan to add the crankcase heater.

I will change the thermostat to a new digital design that limits cycles per hour to correct short-cycling.

Hi Larry,

Not trying to teach you again as I know that you've learnt a lot and it's your home too but...

A good pressure test is required for a leak free system. A vacuum test is for moisture.

It might be worthwhile adding a heater to the accumulator as well.

You could just include a delay timer in the compressor circuit if that is easier/cheaper.

[Larry2]

Brian, I so much appreciate your help and those other professionals here on this site. Every time I visit, I learn something new. Much of it is not in text books from experience in the field.

I charged the pipes with inert gas as soon as brazed up at 100 PSI days ago and the pressure stayed overnight. Rain was predicted, so i brought my manifold set indoors, leaving the system under pressure. I will have to cut the line to install the reversible filter/drier ahead of the TXV before I continue. I didn't want the new filter connected before pulling a vacuum on the lines. Meanwhile, I have power and thermostat wiring to complete. I will check for leaks again after I add the new filter.

Meanwhile, I've been tinkering with my eBay purchase of a torr meter and DV-4d sensor. Tinkering with this device has been a real education concerning vacuums.



I farted with this for hours last night with the manifold set connected. I was astonished to learn how wet the hoses were. They got better each time I cycled the pump a while. In the long run, I figured out these hoses will never dry out or be leak free enough to call the job dehydrated.

The most amazing thing (call it my imagination if you like) was to elevate a hose as if to pour water out of the hose into the vacuum pump. The gauge would rise and soon the vacuum pump would scarf it up. Then more moisture or leaks dumped more material. Blanking off the system caused it to rise more slowly each time. It was never adequate with any hose connected.

Today, I bought copper flare nuts and copper tube. I was amazed how long it took to evacuate just the tiny tube you see in the photo, enough that the gauge didn't rise with the pump blanked off. When I added the hose that has a ball valve at the end, it was impossible to stay under 1 torr with the pump shut off. An hour of running, it is still rising to 3 torr on a single hose after being blanked off. This is a new hose (the red hose in the photo) and only a few feet long.

I will be fashioning the rest of my pump connections from copper tube and flares.

With the manifold gauge connected and damp hoses, a rise to 20 torr or higher was absolutely undiscernable on the suction gauge. I think few appreciate this. I had one vendor brag he would evacuate to 29 inches before calling it done.