Dodgy TEV ? what do you think?

[TRASH101]

Hello everybody

I have got a Denco 37Kw ish tandem copeland scrolls with remote condenser. Its been working fine then all of a sudden LP faults. The gauges confirm this suction hanging about 25 psi, sight glass full, liquid temp 18 c, discharge 68 c and forst on the distributor and TEV. The condensor fan is doing nothing (ambient -2 to +10 c (@ 10 c suction 30 psi).

First off I checked for leaks (sniffer) found nothing then stripped the TEV (Alco xb 1019 nw-1b two piece) nothing obvious.

started it up problem still there added some gas still no joy.

Any ideas would be most welcome as I am :confused:

[TRASH101]

Sorry its 407c

[nike123]

Hello everybody

I have got a Denco 37Kw ish tandem copeland scrolls with remote condenser. Its been working fine then all of a sudden LP faults. The gauges confirm this suction hanging about 25 psi, sight glass full, liquid temp 18 c, discharge 68 c and forst on the distributor and TEV. The condensor fan is doing nothing (ambient -2 to +10 c (@ 10 c suction 30 psi).

First off I checked for leaks (sniffer) found nothing then stripped the TEV (Alco xb 1019 nw-1b two piece) nothing obvious.

started it up problem still there added some gas still no joy.

Any ideas would be most welcome as I am :confused:

To quickly check a TEV, remove the bulb from the suction line mounting and heat it with warm water, or your hand. Once the bulb is warmed — which falsely causes the TEV to sense warmth and high superheat — the valve should open and flood the evaporator with refrigerant. Suction pressure should rise. The TEV is not controlling flow during this test. Liquid floodback is highly likely if the test takes more than 30 seconds.
A more accurate test can be done on a TEV using a combination of the warming test and a temperature sensor taped to the suction line at the evaporator outlet. When performing this test, make sure to insulate the sensor connection.
By warming the bulb, port opening, the suction line temperature, and superheat to match design conditions, you know the TEV is good if it opens. It's also a good idea to check the capillary tube, since a ruptured tube can lead to lost refrigerant in the bulb.

[TRASH101]

Thanks for you response Nike

Tried it before I stripped the TEV and I have just Tested it again with little or no effect.

[nike123]

Then change power assembly of TEV! I would also change cage assembly.

[TRASH101]

Thanks again Nike

I have been tracking the bits down, at least its an easy job.

It still worries me though because the diaphragm had plenty of rebound and the valve travelled ok in the guide unless the chamber was flooding from the liquid line keeping the diaphragm from pushing the valve open. (or there is a restriction in the TEV manifold/ block) Maybe I didnt look closely enough at the ports:o.

Cheers Nike for reading and responding to my whinging.:)

[chillin out]

Have you checked the liquid line filter?

Also, is there a heat exchanger fitted?

Chillin:):)

[benj2212]

can you feel or hear gas hissing through the valve, prehaps a heat exchanger has collapsed or does it have a drier (blocked?) might sound dumb but i once mistook an empty sightglass for a full one. i presume the air handler isn't frozen. sorry if this is no help as i havent worked on this kit. :rolleyes:

[Andy AC]

Those denco units vibrate quite a bit and seem to leak from all sorts of places. check the plastic pressure control lines for chaffing and all the flare connections on the pressure switches. I had a leak on the fan speed control device once, had to take it out of its mounting position to see it.
Could be your remaining blend of r407c is not as good as it could be.
The capiliaries for the expansion valve heads tend to sway about in the airflow and are prone to rupturing.
If you do sort it, let us know, I've got one go down on suspect tev. The power head was replaced less than a year ago, but appears to have gone again. Customer does not want to pay for us to investigate at the moment. They still have 5 working fridge circuits feeding the room, so not that urgent. - Telecoms company - tight gits

Andy

[TRASH101]

Have you checked the liquid line filter?

Also, is there a heat exchanger fitted?



Hello chillin

The filter seems ok i.e. liquid after it and no apparent temp change but as there is reduced volumetric flow rate I cant comment on it but intend to replace it when I change the power assy. There isnt a subcooler on the liquid line I have put the low temp down to over condensing due to reduced flow rate and poor heat exch on the evap.


can you feel or hear gas hissing through the valve, prehaps a heat exchanger has collapsed or does it have a drier (blocked?) might sound dumb but i once mistook an empty sightglass for a full one. i presume the air handler isn't frozen.

Hello ben
I`ve got a schraeder after the TEV and can see pulsing the sg is definitley full and dont say frightening things like collapsed evaps:eek:.(My poor old heart cant take it!)



Could be your remaining blend of r407c is not as good as it could be.


Hello Andy

Im almost certain the gas is fine as I detected no leaks and I recommissioned this unit myself last year.


If you do sort it, let us know, I've got one go down on suspect tev. The power head was replaced less than a year ago, but appears to have gone again. Customer does not want to pay for us to investigate at the moment. They still have 5 working fridge circuits feeding the room, so not that urgent. - Telecoms company - tight gits

Im not sure about these Alco TEVs they seem to wander on the superheat a little and although this is my first dodgy Alco I have heard some stories about regular failures.As for your customer then WOE BETIDE HIM. As for Denco keep a close eye on the compressor contactors Ive had few lately that have dropped a phase.

[nike123]

Im not sure about these Alco TEVs they seem to wander on the superheat a little and although this is my first dodgy Alco
I changed 5 or 6 ALCO power assemblies in last 10 years.
Also, I changed similar number of Danfoss TEV's and I think they are of same quality regarding malfunction rates.

[Gary]

Did you check the TEV inlet screen?

[TRASH101]

Did you check the TEV inlet screen?


Hello Gary

I checked the inlet side of the manifold (as best I could due to access) and didnt find a screen. Do these Alco TEVs definitaley have a screen because that would explain it all and also make me feel like a proper TW(I/A)T for not spotting it:(

[Gary]

What's the model number on the valve?

[TRASH101]

The model no. is XB 1019 NW-1B

cheers Gary (cant find details for valve on net but wholesaler says it doesnt mention gauze/ filter in their literature)

[Gary]

That number is for the cage assembly. Alco is a division of Emerson. This is a T series valve:

http://www.emersonclimate.com/flowcontrols/pdf/txv/isheets/T-Series.pdf

Hmmm... I'm not seeing an inlet screen in the diagram.

[Gary]

Hello Gary

I checked the inlet side of the manifold (as best I could due to access) and didnt find a screen. Do these Alco TEVs definitaley have a screen because that would explain it all and also make me feel like a proper TW(I/A)T for not spotting it:(

I would start with airflow, but then I always start with airflow. Not spotting an airflow problem would make me feel like a "proper TW(I/A)T"... LOL

[TRASH101]

Of course you are right to label the point about airflow. I always go straight to the fans and in this case there is no issue on evap airflow and unproven, due to negligable transfer, at the condensor.

The link is my valve and now Im concrned about the bleed hole (didnt know that was there:o). I will check that out when I get the new cage and power assembly.

Thanks Gary

[anto]

hello,did u checkpower element by warming it.if it is ok the problem most probably lies with airflow over the evaporator.check drier core also

[grump]

Here we go again DO NOT GET FIXATED ON THE TXV if the job has been set up properly ie it has been pulling down to the set point,make sure every thing is in order prior to messing with the TXV.Air flows,running currents,pressures,defrost,controller,etc ,etc.
The txv is an extremely reliable valve i have used many makes ,in the later years mostly Danfoss so my advice is check out the entire system,leave the valve alone ,do you here me talking to you? GRUMP :D:D:D

[Gary]

Of course you are right to label the point about airflow. I always go straight to the fans and in this case there is no issue on evap airflow and unproven, due to negligable transfer, at the condensor.

The link is my valve and now Im concrned about the bleed hole (didnt know that was there:o). I will check that out when I get the new cage and power assembly.

Thanks Gary

The bleed hole is for equalizing pressures on the off cycle to avoid starting problems. You probably don't need it and it wouldn't cause your problem.

[Gary]

Here we go again DO NOT GET FIXATED ON THE TXV if the job has been set up properly ie it has been pulling down to the set point,make sure every thing is in order prior to messing with the TXV.Air flows,running currents,pressures,defrost,controller,etc ,etc.
The txv is an extremely reliable valve i have used many makes ,in the later years mostly Danfoss so my advice is check out the entire system,leave the valve alone ,do you here me talking to you? GRUMP :D:D:D

In general, I agree with this. The problem is almost never the TXV and everything else should be checked first.

[Gary]

For starters, we need a more accurate description of the symptoms. Low suction pressure doesn't tell us much. If the airflow is okay, then we need to know subcooling and superheat.

[Gary]

Of course you are right to label the point about airflow. I always go straight to the fans and in this case there is no issue on evap airflow and unproven, due to negligable transfer, at the condensor.


You didn't mention the high side pressure. Does the system have head pressure control? There could be insufficient pressure to push the refrigerant through the TXV.

[nike123]

I think that we here overreacting somehow.

First:

sight glass full, liquid temp 18 c, discharge 68 c and forst on the distributor and TEV.Then:

To quickly check a TEV, remove the bulb from the suction line mounting and heat it with warm water, or your hand. Once the bulb is warmed — which falsely causes the TEV to sense warmth and high superheat — the valve should open and flood the evaporator with refrigerant. Suction pressure should rise. The TEV is not controlling flow during this test. Liquid floodback is highly likely if the test takes more than 30 seconds.
A more accurate test can be done on a TEV using a combination of the warming test and a temperature sensor taped to the suction line at the evaporator outlet. When performing this test, make sure to insulate the sensor connection.
By warming the bulb, port opening, the suction line temperature, and superheat to match design conditions, you know the TEV is good if it opens. It's also a good idea to check the capillary tube, since a ruptured tube can lead to lost refrigerant in the bulb.After that:

Thanks for you response Nike

Tried it before I stripped the TEV and I have just Tested it again with little or no effect.I am understood here that he tested TEV as I discribed and that valve doesnt responds by opening.
That concludes that TEV is faulty.
I think that is proper step here to change TEV power assembly and cage.
Dont you all agre with that? Am I mising something?:confused:

P.S. I recently changed one and, as I recollect, there is no screen in them.

[Gary]

I think that we here overreacting somehow.

First:
Then:
After that:
I am understood here that he tested TEV as I discribed and that valve doesnt responds by opening.
That concludes that TEV is faulty.
I think that is proper step here to change TEV power assembly and cage.
Dont you all agre with that? Am I mising something?:confused:

P.S. I recently changed one and, as I recollect, there is no screen in them.

Warming the bulb will flood the coil IF there is sufficient liquid refrigerant available at the TXV inlet and IF the inlet screen is not plugged and IF there is sufficient high side pressure to push the refrigerant through and IF the orifice is large enough to flood the coil when wide open.

That's a lot of ifs.

[nike123]

Warming the bulb will flood the coil IF there is sufficient liquid refrigerant available at the TXV inlet and IF the inlet screen is not plugged and IF there is sufficient high side pressure to push the refrigerant through and IF the orifice is large enough to flood the coil when wide open.

That's a lot of ifs.

I agre, but from reading above posts, it seems to me that lot of these IF are sorted and some of them asking opening of valve (what is already done before). If I open valve, i would certainly changed cage and power assembly regardless of their condition. Lake changing time belt on cars.:)

[TEMPAIRE]

expansion valves rarely fail go back to basics if you have tried the usual stuff recommission. and check the electrical / mechanical side to lp safe guards

[TRASH101]

My word Ive missed a lot

To clarify this scenario

The system has run ok for 5 years barring a leak repair 6 months ago charged with virgin 407c. The airflow is monitored weekly for volume and temp diff for the evaporator. The system generated a LP fault once and will not re-establish good system characteristics.

The subcooling is in excess of 10c evap superheat around 30c compressors LRC around 20% lower than normal I appreciate the subcooling would in itself cause problems but the evap load is still there and the TEV bulb test didnt move the frost past the distributor in fact it didnt change at all so not only did the suction pressure not change the visual indications didnt change (the bulb was warmed to around 35c for about 1 min)

I hope this clears some of the ifs.

(unless of course your discussing general system diagnostics then Gary I couldnt agree more and on previously proven systems all ifs are true where applicable )
p.s. Gary I indicated HPC in original post (its set around 18barg)

[lana]

Hi everybody,

I assume the TEV is externally equalized.

If so check where the equalization line is connected. It should be after the bulb towards the compressor. If it is connected before the bulb and there is an internal leak in the TEV, the valve would close.

I had this experience once.

Also I would agree with Gary, measure everything :

LP is low then you have to look for 4 families of faults :
1- Lack of refrigerant.
2- Lack of TEV capacity.
3- Pre-expansion in the liquid line.
4- Lack of evaporator capacity.

The fault I mentioned goes into second family.

Hope this helps.
Cheers

[Refrigerologist]

Hi guys! I had a number of Alco TEV valve failures on Delonghi water chillers. The client was getting a bit concerned about the number that I had changed in a 2 year period, 3 in all. I had Powermaster Ltd's tech bod, e-mail the facilities manager with his response to my question of why so many failures. He stated the power elements tended to collapse if the equipment was working for prolonged periods under partial load conditions. In fact his company considered the power elements to be a consumable item!!

I had never seen so many failures before. I had only recently taken over servicing the equipment. After changing the drier cores a couple of times, (full system vaccing was not an option due to production times), the problem at least seems to have slowed and hopefully stopped. I have to say that of all the valves I have used the Alco seems to fail far more often than Danfoss or Sporlan.

[Pykester1]

Hi Trash101. Check that the TEV isn't an MOP valve. In MOP valves the phial charge is significantly less than in normal valves, and in certain circumstances the phail charge can migrate from the bulb of the valve to the head of the valve. This then means the bulb has no charge in it so it cannot action the diaphram of the valve when the suction line warms up in response to load changes. Sometimes it can be remedied by warming the head up of the valve and forcing the charge back into the bulb.
Hope this helps.

[Allrounder]

[quote=Refrigerologist;98809]Hi guys! I had a number of Alco TEV valve failures on Delonghi water chillers. The client was getting a bit concerned about the number that I had changed in a 2 year period, 3 in all. I had Powermaster Ltd's tech bod, e-mail the facilities manager with his response to my question of why so many failures. He stated the power elements tended to collapse if the equipment was working for prolonged periods under partial load conditions. In fact his company considered the power elements to be a consumable item!!



I'm glad someone else has had this problem on de Longhi awful rubbish chillers. When I had similar problems Powermaster refused to admit there were issues. I had a site where a shell and tube evaporator failed because of high superheat, it froze the water in the first part of the chiller from the TEV and folded the copper tube inside the end plate. (I'm sure the 407c glide didn't help) I have also repaired lots of these valves where the cage was sticking then moving making the superheat jump around.
At least they are easy to service and HRP keep good stocks.

[Denco Technical]

Looking at your original post is it only cold ambients where this happens?

If so is the LP delay set up correctly?


Whats the suction/discharge pressure when you are running at 50% (1 compressor)?

What is your airflow (accurate)

90% of issues like this is airflow i am afraid.