Fault on an Airedale unit

[marc5180]

Got called to a unit today that wont run. Its an Airedale condensor with AHU indoor unit about 5 meters away, controlled by a trend controller. set the set point down to bring the AC on but it went off on an LP fault so bridged out the LP put the guages on and the suction was pulling a Vac. As it was on R407c i decanted the refrigerant thinking it was short of gas but it wasnt so ithen vacced out and recharged it. The unit itself has also got what looks to be a hot gas bypass that has been fitted after production looks like an expansion device but bigger and im not really familiar with working on these. Then when i switched it back on i had the same pressures as before 0 bar on the suction and 10 bar on the liquid ( theres no port for the discharge) Now heres the confusing part.... When i take the temps on the condensor i get discharge temp from compressor of 88deg, liquid temp 23dec, and suction temp 17 deg. and Hot gas bypass 31deg..... Then on the AHU indoors on the liquid before TEV 16deg, after TEV i get -25 and the hot gas bypass i get -25 also??? and the suction i get 16 degrees... Hope iv not confused you all with the temps but iv took them everywher i can. Any ideas?:confused:

[ConDor]

Blocked filter dryer, defektive tev, or closed magnet valve?

[marc5180]

Blocked filter dryer, defektive tev, or closed magnet valve?

there is no filter drier on it solonoid valve is open, the TEV temp going into the evap is -25 and coming out on the suction is 16degs? but the hot gas bypass that goes into the evap is also -25??????? Then on my suction guage im getting 0bar?:eek:

[Lowrider]

Have you tried to get the tev open? If you take the bulp off the suction line and hold it in your hands, the tev should open. If it isn't the bulp might off and you'll have to replace it, but I always replace the entire tev!

Afterwards do a good pressure check and evac the system completly and then start by filling the amounth of R407c as indicated on the nameplate, but remember, fill as liquid in the liquid line since it's a blend!!!

Good Luck!

No worries abouth the pm!!

[marc5180]

Have you tried to get the tev open? If you take the bulp off the suction line and hold it in your hands, the tev should open. If it isn't the bulp might off and you'll have to replace it, but I always replace the entire tev!

Afterwards do a good pressure check and evac the system completly and then start by filling the amounth of R407c as indicated on the nameplate, but remember, fill as liquid in the liquid line since it's a blend!!!

Good Luck!

No worries abouth the pm!!

If the tev was closed though then that would account for the suction guage pulling a vac wouldnt it but if thats the case if you feel after the TEV its -24deg where as just before the TEV its 16degs which makes me think it is working just maybe not correctly. Iv worked out that the superheat is 17 how do i get it down to around 7? Do i screw the nut in or out?


Also with regards to the Hot Gas Bypass the solonoid seems to be energized most of the time but i thought the aim of it was to give hot gas to the evaporator when needed???? but where it goes into the evaporator im getting -25 degs again so it isnt hot gas???

[Lowrider]

If little liquid is evaporated in the tev, it will freeze after the tev. Srewing it in will decrease the superheat, out will decrease it!


Most of these unit's will also open the hot gas bypass if the suction temp is to low!

If you take one off the wire's off the hot gas bypass solenoid it should close, plaese check this too!!

[TRASH101]

hello marc

have you double checked that this system isnt a pump down system ?
a lot of airedale systems that i have come across seem to be configured this way.
if not perhaps there is debris at the orifice on the TEV

the hot gas is probably rigged as capacity control (might come straight off the trend)

is this a CUS model?

[marc5180]

If little liquid is evaporated in the tev, it will freeze after the tev. Srewing it in will decrease the superheat, out will decrease it!


Most of these unit's will also open the hot gas bypass if the suction temp is to low!

If you take one off the wire's off the hot gas bypass solenoid it should close, plaese check this too!!

I replaced the solonoid coil today as someone who had been to it previous had left it off and not put it back on so when it got a signal it just melted it. Checked this and it did open and close

[marc5180]

hello marc

have you double checked that this system isnt a pump down system ?
a lot of airedale systems that i have come across seem to be configured this way.
if not perhaps there is debris at the orifice on the TEV

the hot gas is probably rigged as capacity control (might come straight off the trend)

is this a CUS model?

How do i check weather its in pump down mode? the unit has worked previously so im told. Opened the TEV up today to check for any debris but it was ok..

[Lowrider]

So we can asssume the trend controler and bypass do there job! The only reason it has a low gas pressure can be if the tev is not opening!

It is an aircooling unit?

[marc5180]

So we can asssume the trend controler and bypass do there job! The only reason it has a low gas pressure can be if the tev is not opening!

It is an aircooling unit?

It is yes, can i open the Tev fully to get the pressure back up and then close it slowly turn by turn?

[marc5180]

So we can asssume the trend controler and bypass do there job! The only reason it has a low gas pressure can be if the tev is not opening!

It is an aircooling unit?

I thought the bypass was supposed to send hot gas down to the evaporator but by the time it gets there im getting a temp of -25 ( thats not hot gas) the same as the liquid temp after the TEV

[Lowrider]

If you checked that heating the bulp opens the tev, then yes you can turn the screw, but do it slowly! 1 turn at a time and measure suction pressure and temperture and get it between 4 and 10 K!

But do check the evap if difference between entering and leaving air is about 12K if superheat is ok! If it's too high it might be dirty or the fan is not pulling enough air!

[Lowrider]

that depends, if the hot gas bypass is between the discharge line and suction line, it's there to get the suction up!

[marc5180]

that depends, if the hot gas bypass is between the discharge line and suction line, it's there to get the suction up!

The hot gas bypass comes off the discharge but then it goes into the evaporator and i cant see where it goes then because i cant look at the coil only the front and back of it. All i know is the HGB seems to go in at the top with the liquid a few inches under it and the suction about 12 inches furthur down but to the right

[Lowrider]

What are entering and leaving air tempertures if unit is runnign?

[marc5180]

the unit only runs when i bridge out the LP switch and i dont like to leave it running for long but for the time that i did i had air off temp is 22degs with an air on of 20degs

[Lowrider]

So it's going out hotter than it's getting in!

Have you checked the tev is opening if bulp is warm? Put it in the outgoing air and start the unit. If pressure is coming up, the tev should be adjusted, if not replace the tev!

[TRASH101]

has the hot gas valve got a small "tap" line connected to the suction line ?
if not it is definately capacity control rather than suction pressure maintenance

this will work off spring pressure only

if your not getting discharge temp across the hot gas valve the solenoid aint open or the valve aint

i would probably open the superheat fully to get the the suction up but be careful that it dont flood back on you and then you got the problem of setting the correct superheat :D

[marc5180]

Had a look at th bulb found it insulated on the suction line but i didnt take it off and warm it up, so could it be that the TEv is closed to much and is starving the evap with liquid causing the suction pressure to be pulling a vac?

[TRASH101]

the tev really does sound bad you sure there is no possible way the system is being restricted

[Lowrider]

Take off the insulation carefully, remove the bulb and check if the tev opens! If not you'll know the problem!!!

Wish you good luck, I'm off to bed! Alarmclock goes off in 5 hours!!

[marc5180]

has the hot gas valve got a small "tap" line connected to the suction line ?
if not it is definately capacity control rather than suction pressure maintenance

this will work off spring pressure only

if your not getting discharge temp across the hot gas valve the solenoid aint open or the valve aint

i would probably open the superheat fully to get the the suction up but be careful that it dont flood back on you and then you got the problem of setting the correct superheat :D

The HGV does have a quater copper line going into the suction line in the condensor

[marc5180]

the tev really does sound bad you sure there is no possible way the system is being restricted


theres nothing else to cause a restriction just the TEV and a sight glass, no drier or in line solonoid etc....

How would i adjust the hot gas bypass? Is it the same as a TEV or should i not mess with it?

[TRASH101]

i cant see why the tev wouldnt open sufficiently from the eq. line as the bulb temp is going to be higher than design temp anyway.

there has to be a blockage or restriction somewhere

[TRASH101]

i might have to learn to type with more than one finger at this rate

the hot gas valve will have a plastic or copper cap that threads into the housing. beneath this lies an adjuster (youll probably need a 10mm allen key) this adjusts the spring pressure on the diaphram wich is also ported to the suction tap in (when used). if you screw this in it acts like increasing the superheat i.e. increasing the volume passing through the valve and as the suction pressure increases the tap line pushes against the spring to decrease the volume. you will have to set this up when you get the bloody thing running right and make sure its isolated if you have to re commission for charge or setting the tev and be sure that you find out why its there

[coolments]

Hi

Curious to know the model of the unit and how much refrigerant you put in, all the readings you indicated in your original post lean me towards it not having enough gas charge

assuming virgin refrigerant added from vaccuum

'0 bar on the suction and 10 bar on the liquid' symptom of not enough refrigerant i would be looking for 4 bar suction and around 17 bar liquid.

'discharge temp from Compressor (http://www.refrigeration-engineer.com/forums/glossary.php?do=viewglossary&term=60) of 88deg' over heating comp due to not enough refrigerant for suction cooling to satisfy.

'liquid temp 23dec' low temp again low charge symptom should be around 45 ish.

'suction temp 17 deg' low charge symptom (around 11 ish witha 6-7k super heat).

and Hot Gas Bypass (http://www.refrigeration-engineer.com/forums/glossary.php?do=viewglossary&term=76) 31deg ..... Then on the AHU indoors on the liquid before TEV 16deg, after TEV i get -25 and the Hot Gas Bypass (http://www.refrigeration-engineer.com/forums/glossary.php?do=viewglossary&term=76) i get -25 "ect ect".

also what is the condenser motor running like, they usually have fan speed controllers with two adjustment screws on for setting high pressure. if the fan is realy slow then experiment by adding more gas, these units cannot have gas weighed in as there is normally no data plate for the amount, it has to be gauged by the engineer commissioning it.

If running flat out then it is not set correctly or broke and vastly over condensing. if this is the case then turn the temp set point to the lowest point, it should then be running on the min fan speed set point, adjust this so the fan is not stalling ang keeping a high pressure reading of around 270 psi then throttle up the temp dial until the pressure settles at around 245-255 psi it should then keep a steady head pressure and regulate condenser fan speed. if they are none responsive and the fan is running flat out no matter what you do then try improvising and blocking off part off the condenser coil to see if you can get the pressures to rise.


if this sysyem does not have any receivers or accumaltors as many dont then the HP fan speed control set point and gas charge has to be exact for the system to work. If your confident on this then with out being on site i am scratching my head.

Thats my thoughts any way

Good luck... i am away for 4 days now but will check back to see if this is resolved...curious.

[marc5180]

i might have to learn to type with more than one finger at this rate

the hot gas valve will have a plastic or copper cap that threads into the housing. beneath this lies an adjuster (youll probably need a 10mm allen key) this adjusts the spring pressure on the diaphram wich is also ported to the suction tap in (when used). if you screw this in it acts like increasing the superheat i.e. increasing the volume passing through the valve and as the suction pressure increases the tap line pushes against the spring to decrease the volume. you will have to set this up when you get the bloody thing running right and make sure its isolated if you have to re commission for charge or setting the tev and be sure that you find out why its there


Got back to the unit this evening but only for an hour i was looking at the hot gas bypass valve and the head was screwed in (closed) totally, surely this isnt right?

I checked the fan and it was running a little so i turned it down and the liquid line started to hunt erratically between 10bar and 15 bar. Im not able to get a discharge pressure as there isnt a stub to connect to.

[marc5180]

Also i took the panel off so i could see the pipes as they went into the Evaporator. Would it matter if the hot gas bypass and the liquid line were installed the wrong way going into the evaporator? The liquid after the expansion device goes towards the distributor but here the HGB meets it but theres no solonoid valve or anything to stop the liquid going down the HGb line...Is this normal..
Does any one know?

[coolments]

Hi

that sounds like the correct arrangment for hot gas bypass although i still would expect a solenoid in there at some point, after all they are usually installed to reduce the cooling duty for close control aplications, you say the the condenser fan was running a little slow and you throttled it down more and it started to hunt, sorry still i feel there is not enough refrigerant in there.

probably best to leave the hot gas valve fully closed at this point and try to get the unit working before messing with it, assuming a size CU6 condenser i would be looking around 12kg of gas, how much is in there at the minute.

[puddleboy3]

Also i took the panel off so i could see the pipes as they went into the Evaporator. Would it matter if the hot gas bypass and the liquid line were installed the wrong way going into the evaporator? The liquid after the expansion device goes towards the distributor but here the HGB meets it but theres no solonoid valve or anything to stop the liquid going down the HGb line...Is this normal..
Does any one know?

As already pointed out this sounds like the correct arrangement for a hot gas bypass setup and I wouldnt think there would be any problem with not having a SV fitted. The fact that the HGB is shut right down I would disregard the HGB valve the now and concentrate on getting the system running. To answer your question about the liquid going own the HGB line, yes this setup is normal as your discharge pressure is going to be higher than your liquid pressure at the evaporator. If you are sure the system has the correct amount of refrigerant in it then I would stop messing about with the HGB valve that if faulty or connected up wrong would increase your suction pressure not the opposite. Ive had problems with airedale expansion valves before so thats where I would be looking. The fact that there is no filter drier fitted is worrying. Which is going to mean that if OFN wasnt used when the system was installed all the crap is going to be neatly bundled up at the EXP.

Good luck and like everyone else im now curious

[coolsaj]

Got called to a unit today that wont run. Its an Airedale condensor with AHU indoor unit about 5 meters away, controlled by a trend controller. set the set point down to bring the AC on but it went off on an LP fault so bridged out the LP put the guages on and the suction was pulling a Vac. As it was on R407c i decanted the refrigerant thinking it was short of gas but it wasnt so ithen vacced out and recharged it. The unit itself has also got what looks to be a hot gas bypass that has been fitted after production looks like an expansion device but bigger and im not really familiar with working on these. Then when i switched it back on i had the same pressures as before 0 bar on the suction and 10 bar on the liquid ( theres no port for the discharge) Now heres the confusing part.... When i take the temps on the condensor i get discharge temp from compressor of 88deg, liquid temp 23dec, and suction temp 17 deg. and Hot gas bypass 31deg..... Then on the AHU indoors on the liquid before TEV 16deg, after TEV i get -25 and the hot gas bypass i get -25 also??? and the suction i get 16 degrees... Hope iv not confused you all with the temps but iv took them everywher i can. Any ideas?:confused:
You have a blockage in the low side. Dont panic at all! check for obvious signs if drier fitted, evaporator tev good luck

[marley821]

Sounds like the power assembly of the expansion valve has gone to me. Had this type of fault a few times with Airedale units.

Decant, new drier, new valve, pressure test, vac recharge-away you go!

These systems are not that complicated so don't get bogged down with it!!

[marc5180]

Hi

that sounds like the correct arrangment for hot gas bypass although i still would expect a solenoid in there at some point, after all they are usually installed to reduce the cooling duty for close control aplications, you say the the condenser fan was running a little slow and you throttled it down more and it started to hunt, sorry still i feel there is not enough refrigerant in there.

probably best to leave the hot gas valve fully closed at this point and try to get the unit working before messing with it, assuming a size CU6 condenser i would be looking around 12kg of gas, how much is in there at the minute.


At the minuite there is 5kg of R407c. Iv been told by an engineer ( i dont beleive it to be true but il find out) That if i vac a system out, i can dump in as much refrigerant as the system will take as the system will never take more than it needs ( if that makes sense) and if that is the case when i vacced it out previuosly and i added 407c in after the vac when i had added the 5kg there was still a vaccum in the system...i.e i could have gotten in more... Is this true?

[marc5180]

I havent been back to the unit siince last friday, iv ordered an expansion device, and im going to change it and whilst the gas is out im going to braize 2 stubs in before and after the evaporator so

1) i can blow through the evap to check theres no blockage
2) i can check subcooling properly

As soon as i go to the unit next ( when the TEV comes in) then i will come back and post the results. Thanks for all of you that has helped me, its much appreciated
Cheers;)

[frank]

At the minuite there is 5kg of R407c. Iv been told by an engineer ( i dont beleive it to be true but il find out) That if i vac a system out, i can dump in as much refrigerant as the system will take as the system will never take more than it needs ( if that makes sense) and if that is the case when i vacced it out previuosly and i added 407c in after the vac when i had added the 5kg there was still a vaccum in the system...i.e i could have gotten in more... Is this true?
Consider that you have a small split with a small internal volume. When you introduce refrigerant from your bottle into a vacuum, the system will equalise to the bottle pressure. On a cold day this will transfer less refrigerant than on a high ambient day.

On a large system, this will also be true.

You will transfer different amounts of refrigerant to different sizes of systems depending on the bottle temperature. Whether this will be sufficient refrigerant for the system, well, this can only be answered by taking operating temperture measurements.

I often put a bottle of refrigerant into a bucket of warm water on cold days to speed the charging process.

How can you add 5kg into a system and there still be a vacuum?? :confused:

[marc5180]

How can you add 5kg into a system and there still be a vacuum?? :confused:

I mean that after adding 5kg of refrigerant, the refrigerant bottle hadnt equalized with the system yet so the was still more refrigerant that could be transfered into the system

[marc5180]

So is it true or not?

[Brian_UK]

- - - No - - -

[monkey spanners]

No it isn't true that a system will only take what it needs. In cold weather with a warm bottle it'll take way too much. In warm weather with a cool bottle it won't take anywhere near enough. And somewhere in between you might just be lucky......

Jon

[coolments]

Hi Marc

You still havent told us the model of the condenser and AHU yet, need this info to help more. also interested to know the suction and liquid line size

[marc5180]

im going back on monday so i shall let you know. i do know that the liquid line is half inch and i think the suction is either 3 quarter or 7 eigth. Iv been told the unit is 16kw. Il know more Monday
Cheers

[marc5180]

Went back to the unit today, decanted the refrigerant..put in a new drier and braized some charging stubbs in the discharge and after the TXV. Replaced the old TXV for a new one and pressure tested then recharged... the pressures seemed fine and the aire off was 7degC Took a subcooling reading i.e before the condensor (discharge) and after the condensor (liquid) and got 8degC of subcooling.

Now when it comes to Supeerheat which way should i measure it because i took the temp from after the TXV= 2degc then after the evaporator which was also 2degc... i then tried to increase the superheat by turning the TXV screw in half a turn i then waited for ten mins but the temps didnt change...am i doing it wrong???? I want to learn how to commission it properly as many people in the game dont care, they would just install it and leave
thinking the job was done, im not one of them...

[Jase]

Measure temp @ TEV bulb on suction line and take pressure reading @ port on evaporator; from this compare the sst according to the pressure. Once you have this data you can then calculate superheat, (suction line temp - SST = Sh)
Providing no other alterations have been made to the unit i.e air volume differs from design spec then setting up the system should not be a problem.
BTW set the TEV back to original setting and take it from there.

Regards
Jase

[marc5180]

Measure temp @ TEV bulb on suction line and take pressure reading @ port on evaporator; from this compare the sst according to the pressure. Once you have this data you can then calculate superheat, (suction line temp - SST = Sh)
Providing no other alterations have been made to the unit i.e air volume differs from design spec then setting up the system should not be a problem.
BTW set the TEV back to original setting and take it from there.

Regards
Jase

Cheers Jase but one question, i thought to take the evaporator superheat i had to take the pressure before the evap and then the temp after the evap. From what you describe im only taking the temp after... is this the best way to take the evaporator superheat....and did i take the subcooling correctly or is there a nother way to take this also
Many Thanks
Marc

[Jase]

Marc,
The method you use is acceptable but I always prefer checking superheat with means of gauge pressure (sst) and thermometer. Regarding the measurement of subcooling, again I would take condensing pressure (sdt) reading and liquid pipe temp readings to calculate.
The temperatures @ the indoor unit appear to be quite low. Is there adequate load onto the unit? Airflow normal?

Jase

[marc5180]

Yes theres load on the unit, i put the set point down to 10 degC the only thing i found is that 1 of the belts have snapped(there are 2 belts) im im returning tomorrow to change these but other than that airflow seems fine, everythings working that should be

[coolments]

Hi Marc

Jase has told you about super heat but here is how i explain how to get it, not good with figures and formulas etc just hands on explanation from me.

put your suction gauge on the suction Service Valve (http://www.refrigeration-engineer.com/forums/glossary.php?do=viewglossary&term=94) closest to the evapourator (make sure the gauges are the correct type for the refrigerant) look at what pressure it is and follow the gauge pin and write down the temperature shown on the gauge at that pressure. Use a thermosat and take a temperature reading of the suction pipe as it leaves the evapourator and write that down.

Pipe temperature minus gauge temperature equals super heat reading

You should be looking to get around 6 to 8 degrees c for correct super heat in AC aplication.

trying to run the unit any lower than 18c cooling set point will cause you dificulty in commissioning as the regrigerant boiling point temp will get to low and cause the EXP to close, you may over charge at this point. Try turning the unit off for a while and let the room warm up a bit. the EXP will have been factory set for the correct super heat from factory hopefully you remembered or logged how many turns you have adjusted it, if not you will have to play/adjust to suit.

You are loking for around 250psi head pressure (regulated by Fan speed controller on CU)and around 60psi suction when room at around 20c with a 6-8 temp diff for super heat.

just play with the system untill correct. Good luck

[marc5180]

Cheers Guys much appreciated:D

[Gary]

Keep in mind that superheat temperatures can only be set accurately at design space temperature (normal load). If the space temp is high (high load), the superheat is supposed to be high. If the space temp is low (low load), the superheat is supposed to be low.

[marc5180]

Thanks guys for all of your help;)
Much appreciated:D