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bad txv? (23 Posts)
bad txv?i got a call today for no ac on a ten ton, single compressor,r22,heat pump.the pressures were 104 suction,175 discharge,and 175 at the liquid line valve.the superheat was 23 degrees and the subcooling was 2 degrees.there was no temperature drop across the liquid line drier,and the indoor check valve on the air handler was definitly holding as there was a noticable temperature drop across the body of the check valve.the only thing that i can think that this is a stuck open indoor txv.i have ruled out a leaking reversing valve because the touch test proved the valve was not leaking and i have also ruled out the compressor's valves, because if you block the condenser the head pressure goes up.the txv is the only thing that i can think would be causing this no cooling condition.any suggestions would be much appriciated
TXVWith 175psi head the air into the cond coil had to be close to 70*. Did the head go up to 280psi? What was the running load amps? If under name plate amps then possibly bad suction reeds. Was that evap coil superheat or @ the comp S.H.?.This post was edited by an admin on May 4, 2012 7:28 PM.
Not a Bad TXVIf the TXV was wide open, your evaporator pressure would be high, but your evaporator superheat would be close to zero.
In order to determine the problem, please provide the following:
Condenser saturation temperature:
Evaporator saturation temperature:
Condenser Outlet (liquid line) temperature:
Evaporator outlet (suction line) temperature:
Outside ambient temperature:
Return air temperature:
Temperature of the four ports (line connections) on the four way reversing valve:
The problem sounds more like a leaking reversing valve than a bad txv. With the above information, we can get to the bottom of the problem.Eugene
Not bad numberNot bad number if there is a heavy load on the system.Wonder what the indoor ambient and wet bulb temp are.
With a heavy load you could see high superheat and high suction numbers.And with a txv you could even be undercharge and that high load and the txv will have you assuming something wrong other then being undercharge.
The low subcool temps drew my attention.I am going with heavy load and low on refrigerant..
AgreedAs I always say, Don, we need a complete set of readings to narrow the possibilities.
We can definitely speculate about al of the possibiliies, as there are many. I too am curious about the rest of the numbers.
This is a perfect example of why it's important to obtain all pertinent readings to ensure an accurate diagnosis.
I always relate this story to my students:
You go on a "no cooling" call. Let's say it's an older R-22 system with a capillary tube. The outside ambient temperature is 90 degreees and the indoor air temperature is 80 degrees. You gauge up on the system to find the operating pressures lower than desired (196 psig/100 degres on the high side, 55 psig/30 degrees on the low side). You immediately determine that the system is undercharged and proceed to add refrigerant to the unit.
Adding refrigerant causes the gauge readings to change only slightly, if at all, so you add more refrigerant. Still very little change. So you add more refrigerant and the operating pressures rise slightly. So you add more refrigerant. The operating pressures are still way too low, but you determine that the system is cooling a little better than it was and a little cooling is better than no cooling.
You prepare the bill and present it to the customer. She goes to the other room to prepare your check and you decide, while you are waiting, to check the air filter. At the filter, you realize that the homeowner can easily knit a sweater with all of the junk that is on the filter. You pull the filter out and the massive suction falls just short of pulling your hat into the return duct.
The light bulb immediately goes on as you rush out to the condensing unit. After gauging up again, you see that the operating pressures are through the roof. Now you have to remove all of the refrigerant that you put into the system.
A superheat calculation would have, along with the return air temperature and the evaporator saturation temperature, helped to avoid this mistake.
Nice Point Eugene.I read the OP and immediately thought Air Flow.
Way too many technicians think refrigerant first. I tell my guys to always look at the whole system. But start with the basics, is there enough airflow to facilitate change of state in evaporator? The kinds of problems described in the OP could easily be caused by a clogged filter, a slipping belt on a belt drive system, an undercurrent situation causing the evap fan to spin too slowly.
The morale of the story is don't always assume that the problem is with the refrigerant cycle.
Bad TXVWith 2* of S.C. ,doesn't that indicate a full or almost full liquid line? as compared to having activity in the liquid line giving 0* S.C.? I mean lots of activity not just a little!This post was edited by an admin on May 5, 2012 12:39 PM.
AirflowIf airflow was the issue the suction pressure would be far lower then what he has and even the superheat would be lower as well.
Hi techman to me the low subcool temps are saving she low on refrigerant are the condenser is dirty but then his head pressure would be alot higher then it is.Then again maybe not being he is low on refrigerant.Assume of course.
Personally I think closer to 12 degree subcool assure a colum of liquid headed to the evaporator coil.Two degree subcool indicate not enough refrigerant or their some poor transfer of heat going on.
Yes teacher i know one should not assume without all the fact, however it great to throw darts now and again to see if we hit the bullseye with our eyes closed.lol
donlol alot.Yes teacher .
You like?I am just going on my experience over the years.Remember when we went from txv to fixed metering system? I went to many of system with fixed metering that read high superheat and normal subcooling.And always had to determine is it cause by a big load on the system or under charge?
And in his case he has a txv and very little subcooling.I am pretty sure he is sending some gas bubble to that metering device.A site glass would be nice only to get a guage as to what is going to the indoor coil.Ten ton system should have one.
As for the wetbulb temps it lets one know the total heat in the air which helps with the other numbers involved when dealing with capacity.
Darts?Did someone say darts? I love that game.
Indeed Don...It is definitely fun to throw them and see how close we get!
How are things down in lovely Virginia?Eugene
VaHi Eugene.all is well now that we got that little heat wave that came thru.How are you and yours?
Doing Great!Semester is winding down, getting ready for a relaxing (more or less) summer. Getting the backyard ready for barbeque season!
Alarm clock.Glad to see i am not the only one that is used to getting up without the alarm clock.You can always tell who old school when they are the first to leave for work.lol
Forget the bbq, strap that tool belt back on and come help us out.
thanksi am going back to the job monday and am going to get some more information.thanks to all for the help.the more i think about it it may just be low on refrigerant.that's what i am hoping.i just bought a new leak detector and would like to try it out.i just don't recall every seeing a system with a txv run such a high suction pressure if it were low on refrigerant.thanks again.
Bad TXVBeing REAL LOW on freon would allow hot vapor to be in the entire length of the liquid line and into the TXV and into the low side of the system raising the low side press up a lot. But 104 is awfuly high. Looking forward to find out what you find out on Monday!
don and Professor, I too, was up early(normal) but I kept quiet to not disturb those who do sleep late. lol.This post was edited by an admin on May 6, 2012 1:06 PM.
delta tZep.A quick check would be to check your delta t between return air and suction line temps.Suction line temps should be any where from 18 to 22 degrees below entering air temps.
Good thing with this is that the suction line temps will not change with any change in indoor humidity.
As for never seeing suction line pressure that high.I have been to gas station where the load was design for the envelope.Then they add drink dispenser and ice-makers,soda cooler that put out lots of heat, the pressure high and low would be so high that it would trip on hps after 15 minutes of run time.
The inside load changes most everything and the evaporator is always the boss.unless she low on refrigerant.
Hope this helps and good luck with your search.
inefficent compressori returned to the job today.it looks like i made a snap decision on friday without gatering all the facts.i started the unit today and took the following readings: 85 suction and 120 head.
compressor amps- 16 fla-38
discarge temp.into the rv- 106
line off the rv going to the condenser-107
line off the rv going to the evaporator- 61.5
line off the rv going to the suction of the compressor-62
suction line temperature at the suction service valve-59
liquid line temperature-63
condenser sat. temperature-69
evaporator sat. temperature-51
i added 4# of refrigerant in an attempt to increase the subcooling.this made no differance to the subcooling or the pressures.with the above information all i can see is a compressor that is not pumping at full capacity.it is only operating at a 35 psi differantial,and the shell of the compressor is the same temperature throughout.it is warm to touch even where the suction line connects.i can't see any other reason then a compressor that has bad valves.thanks to all,i did not spend enough time on this friday,that what happens when you rush without taking the proper readings.thanks again.
Back down the chargeDid you try backing down the charge into the condenser? And are there any unloader on that compressor?
Sure does sound like you are on the right track.usually will see low amps and very high compressor temps.it sure sound like the capacity is lost.
zepfanwhat was the O.D. temp there last friday? Thats a big change in pressurers.This post was edited by an admin on May 8, 2012 7:47 AM.
updatei changed the compressor out today, and that took care of the problem.thanks again for everyone for the help.this is the fourth compressor that has been installed in the unit in 13 years.the first by myself.obviously there is a system problem,i am going to take some airflow measurements on the air handler,and will update on how things are going.thanks to all.
Hay zepI like jobs like that!. By chance did you measure the ammount of oil in the bad compressor? And did you test the oil for acids?
oil was okan acid test on the failed compressor was negative,and the old compressor was full of oil.all things point to airflow.the line set for this unit is only about 30' was very little low points (a nice straight run) my next step is to take some air flow readings on the air handler,i have the fan curve and hope to return to the job on friday.thanks