Problematic TEV ?

[nevgee]

This is a tail from which I would appreciate your comments.

A dehumidifier/ heat pump serving a swimming pool was causing problems for the user. It was apparent the dehum function wasn’t working. He called out a local guy to have a look and upon inspection the compressor was condemned. The client decided to get a second opinion.

We attended and found the compressor didn’t run but further checks found the contactor had lost a pole and so wasn’t switching the compressor. We replaced the contactor, checked out the other controls and functions, the machine settled down to normal parameters, seemingly a job well done and the client was happy he wasn’t facing a hefty bill for a compressor change.

Three days later I get a call from the client telling me the humidity level in his pool hall has shot up again to 85% and not falling. (typical Rh in a pool hall with cover over pool would be holding at 30 - 40% other variables etc being discounted.)

When I arrive at the site I find the compressor running, quite hot to touch, and ice had formed on the pipework from the TEV along the distributor and capillaries to the evaporator tube ends. The whole of liquid line from the condenser to the TEV showed no signs of temperature drop at any point.

The ssp was 2.5b and sdp at 12b. superheat 25C liquid sub cooling 8C (R407C)

The fan was running and appeared to be delivering adequate air, this unit had run for over 4 years without any problem.

The basics of this unit is to dehum recirculated air from the pool hall and then to reject heat back into either the pool water, thru a coaxial heat exchanger or into the air, depending on the control demand.
The unit is charged with R407C, has a ¾ HP single phase, pse start compressor with time delay start. The discharge gas is diverted to either the water condenser or air condenser via a reversing valve. Each condenser then drains thru a Magnicheck valve teeing onto a Parker receiver drier then directly to the TEV (externally equalised). The TEV expands into a refrigerant distributor with 4 capillaries into the evaporator.

Pool water at 28C and returning air at 29C

Further examination of the unit showed the power element of the TEV, a Sporlan 2Tr oem non adjustable, was severely corroded and the main cover of the diaphragm would flake away at touch.

The opinion here was that the power element could have lost its charge and the TEV was holding partially closed.

We recovered the gas charge and purged with ofn, removed the power element and the internals of the valve, leaving only the body in place, and replaced with new components. Vac out the unit, to approx 7 Torr as we assumed there would have been no risk of ingress of moisture, (all components were at ambient or above and there was slightly positive pressure at all times in the system) then regas to the manufacturers weight and set back into operation.

The unit started up ok with ssp at 4.5b sdp at 17 b, super heat at 6C and subcooling at 3.5C all appeared well. The next day we get a call from the client to advise his %RH was back up at 85% !

On returning to the site we find a repeat of the previous conditions. Low suction, low discharge, high super heat high subcooling, no apparent delta T on the liquid line or drier and ice formation on the distributor and capillaries.

This one is proving to be a mystery and I’m wondering if I have lost the plot, :confused: I have another idea which might prove correct but the reasoning may appear obscure, but I need to prove it first.

I would be pleased to read any comments you guys might have.

[Toosh]

This is a tail from which I would appreciate your comments.

A dehumidifier/ heat pump serving a swimming pool was causing problems for the user. It was apparent the dehum function wasn’t working. He called out a local guy to have a look and upon inspection the compressor was condemned. The client decided to get a second opinion.

We attended and found the compressor didn’t run but further checks found the contactor had lost a pole and so wasn’t switching the compressor. We replaced the contactor, checked out the other controls and functions, the machine settled down to normal parameters, seemingly a job well done and the client was happy he wasn’t facing a hefty bill for a compressor change.

Three days later I get a call from the client telling me the humidity level in his pool hall has shot up again to 85% and not falling. (typical Rh in a pool hall with cover over pool would be holding at 30 - 40% other variables etc being discounted.)

When I arrive at the site I find the compressor running, quite hot to touch, and ice had formed on the pipework from the TEV along the distributor and capillaries to the evaporator tube ends. The whole of liquid line from the condenser to the TEV showed no signs of temperature drop at any point.

The ssp was 2.5b and sdp at 12b. superheat 25C liquid sub cooling 8C (R407C)

The fan was running and appeared to be delivering adequate air, this unit had run for over 4 years without any problem.

The basics of this unit is to dehum recirculated air from the pool hall and then to reject heat back into either the pool water, thru a coaxial heat exchanger or into the air, depending on the control demand.
The unit is charged with R407C, has a ¾ HP single phase, pse start compressor with time delay start. The discharge gas is diverted to either the water condenser or air condenser via a reversing valve. Each condenser then drains thru a Magnicheck valve teeing onto a Parker receiver drier then directly to the TEV (externally equalised). The TEV expands into a refrigerant distributor with 4 capillaries into the evaporator.

Pool water at 28C and returning air at 29C

Further examination of the unit showed the power element of the TEV, a Sporlan 2Tr oem non adjustable, was severely corroded and the main cover of the diaphragm would flake away at touch.

The opinion here was that the power element could have lost its charge and the TEV was holding partially closed.

We recovered the gas charge and purged with ofn, removed the power element and the internals of the valve, leaving only the body in place, and replaced with new components. Vac out the unit, to approx 7 Torr as we assumed there would have been no risk of ingress of moisture, (all components were at ambient or above and there was slightly positive pressure at all times in the system) then regas to the manufacturers weight and set back into operation.

The unit started up ok with ssp at 4.5b sdp at 17 b, super heat at 6C and subcooling at 3.5C all appeared well. The next day we get a call from the client to advise his %RH was back up at 85% !

On returning to the site we find a repeat of the previous conditions. Low suction, low discharge, high super heat high subcooling, no apparent delta T on the liquid line or drier and ice formation on the distributor and capillaries.

This one is proving to be a mystery and I’m wondering if I have lost the plot, :confused: I have another idea which might prove correct but the reasoning may appear obscure, but I need to prove it first.

I would be pleased to read any comments you guys might have.

Hi Nev Normally when a tx valve element has lost charge it won`t open the symptoms sound like moisture or short of refrigerant, Have you tried heat on the tx valve that is my guess.

tossh:)

[desA]

Was anything done to the receiver-drier? Could it have contained water, or be partially blocked?

[retrof]

Nevgee, You say the unit started up OK and ran good tolerances. It did this twice but what about as the humidity pulls down to the proper levels? What superheat are you running then? Where is the refrigerant at this time? Is it stacked in the condenser or flooding the evap? What are your readings at 60% compared to 85% or 45%?

You are working in an atmosphere which contains 85% humidity yet you are not questioning moisture infiltrating the system. Are you quite certain?

Also, there is a slight decrease in capacity and efficiency using R407C,over R22, which uses POE lubricant so moisture could be part of the equation. We, as techs, have no idea what may have been introduced by others work habits before us.

Should these questions be answered before continuing your diagnosis?

Please excuse my bluntness. This is just the way my mind thinks.

Cheers

[nike123]

Do you have sight glass with moisture indicator?
If not, check if moisture is problem by heating TXV power head with hot air fan and check if pipes on distributor are melting. If yes, you still have moisture problem. By description, moisture is most probably the case. Does the pipe between distributor and TXV is iced too?
Do you have icing problem at other coil and did you measured system parameters when it works as heat pump for pool heating?
If moisture is case, you should change filter dryer as many times is necessary to dry system to acceptable level. For that purpose, you should fit moisture indicator (if not present), isolation valves (before and after filter/dryer) and charge/evacuation port for ease of filter change and evacuation of only filter/dryer.
Also, I would change oil and charge new fresh refrigerant.

[NoNickName]

Moisture is my vote as well. I would not rely on the moisture indicator, though. Squirt some drops of oil from the compressor onto a metal plate and try to ignite it with a sigarette gas lighter. If you hear a popping noise, that's humidity.

[karim9]

i think it is always better when u change the TEX to change the drier too ,i knew it cost but to be sure that there is no more moisture i am i do it always

[nevgee]

Many thanks for the response which confirmed my thoughts. However, RETROF has put the finger on a valid point.

I had made a mistake in assuming there had been no situation where moisture could have gained entry to the system, but for the previous service guy. His incompetence in condeming a good compressor made me then wonder if further poor service techniques had introduced moisture into the system via his manifold gauges. He would have brough cold (January) manifold gauges into a warm humid atmosphere, condensation would have been running off his tools and, possibly, inside his hose lines. If he connected to the system with those lines then it is probable he could have intoduced moisture.

All of the symptoms indicated it and you all confirmed the same diagnosis.

I have since removed the gas charge purged it thru with ofn and put a 100 micron vac on the system which held for an hour without rising.

As for changing driers etc . I would normally have done so but the unit has been positioned into a tight corner with limited access for service work. Removing the existing drier would be nearly impossible without lifting the whole unit out of its installed space, and again there is no room to fit a second drier at its present location.

However, running pressures and temps appear ok now ... time will tell.

Thanks again for your input.:)

[Gary]

What I find most puzzling about this is the suction pressure. Moisture should have put it into a vacuum. Instead, it just lowered the pressure.

Was the TXV inlet screen cleaned/replaced?

[nevgee]

Gary,

An interesting point. A total blockage as you say should have lowered the suction pressure to vacuum.
Thinking back on this I recall there were no real stable conditions as such during the fault period. The back pressure would hover at times ( 2 -3 bar and drop down to to 0 and -0.0 occassionally.

The TEV is a Sporlan oem without strainer mesh. Visual inspection of the internal parts revealed nothing but a very clean valve, slight blackening around the valve seat but nothing else.

I did note that after fitting the new power element the superheat was stable at about 5 C without any fluctuation. I would have anticipated this value to move as the valve modulated. On the last occasion this efect was noticed. Where the superheat would move up to 7/8C and then fall slowly back to 4/5C which I would take as the valve modulating. The only intervention at this time was the vaccing out and regas.

[Gary]

I'm wondering if the valve body might be warped? This should have been a problem since its installation, though. Have they had problems all along?

How is the bulb/phial installed? It should be installed with the cap tube up if possible. This allows the liquid portion of the charge to be stored in the bulb, rather than on the power head.

Also, the bulb should be mounted upstream from the equalizer line.

[Gary]

Is this a single phase compressor or three phase?

I'm wondering about the blackening of the valve seat. If this is a three phase compressor, it could have single phased, burning the oil and forming sludge and/or acids. Or if the contacts were badly burnt on a single phase compressor the same thing could happen. Did the original refrigerant smell burnt?

Since the liquid line drier is inaccessable, you might consider installing a suction line drier. Make that a burnout drier if you suspect sludge/acids.

[retrof]

Gary

In the US it would be rare to have a 3 ph circuit. However, I was considering the same earlier along with your suction drier comment which would bring capacity back into the equation.

Although moisture may not be the issue at hand or the cause it is good practice taught to be safe rather than recall your client.

In closing Gary, did you mean to install the TXV sensing bulb downstream of the eq line instead of upstream? I also like to be sure of clean metal contact and wrap/insulate the bulb away from ambient.

Cheers

[Gary]

In closing Gary, did you mean to install the TXV sensing bulb downstream of the eq line instead of upstream?

No, the bulb should be upstream. If the TXV internal seal leaks, small amounts of liquid can flow through the equalizer line to the suction line. If the bulb is downstream this liquid is sensed by the bulb, causing the TXV to close down and/or hunt. If the bulb is upstream the leakage has no effect on the TXV operation.

Seal materials have improved considerably over the years, so this problem is rare these days. Still... better safe than sorry. It's the sort of thing that can drive you nuts.

[nevgee]

The compressor is single phase (see original post) and had a pole burn out on the contactor. The unit has run without issue since instal (4yrs) and has only become a problem since the local service chappy got involved. He appears to be the only common factor in this case. However I did notice the TEV was installed in a less than horizontal plane. ie, the power element was below horizontal. Taking on board Gary's comment about bulb location and gas migration in the capillary and bulb, there may possibly have been some contribution here. I levelled the valve to horizontal on my second visit, so this should not be a problem now.

The blackening in the valve was ever so slight, nothing in comparison to some i've seen. The gas odor was nothing unsual.

[Gary]

The unit started up ok with ssp at 4.5b sdp at 17 b, super heat at 6C and subcooling at 3.5C all appeared well.

That subcooling seems low. I would add refrigerant until the subcooling is about 8.5K.

[Gary]

The ssp was 2.5b and sdp at 12b. superheat 25C liquid sub cooling 8C (R407C)

That would mean the liquid line at the receiver outlet was about 20C. For that to happen, the surrounding air would have to be below 20C.

I'm not sure that I trust your measurements. Where are you taking these measurements? Was the surrounding air below 20C?

[Gary]

I recall you mentioning that this system has two condensers. I'm wondering if the problem might occur upon switching condensers.

If one of these condensers is an add-on, this would require additional refrigerant, beyond the manufacturers weighed-in charge.

[nevgee]

Sorry for not replying, have been busy just laetely.

The second condenser is water cooled in parallel with the air cooled condenser. a solenoid valve controls a by pass of the water cooled cond. Water temp was not logged at the time but could have been as low as 18 / 20 C.

The unit has been running without issue since my last visit, so it might be there was some moisture in there...

Thanks guys for your valued comments.

[icecube51]

so if i understand it correcly, there is a cind of three-way-valve for the heat rejection (air/water)?? when you puld out the refrig,what was the possion of the valve?? or is it possible to open the valve both ways for say "repairs" or "recover" ??
is it not possible that there was some moistre in one of these "heatrejectors"??

just thinking out loud here see.

Ice