High pressure trip w/ low charge

[KB Cool]

How is this possible on a 30RAP106. The IOM says it could!

This is what it says:

T126 Alert Circuit A High
Head Pressure
Compressor operation outside
of operating envelope. Circuit shut down
Automatic, only after
first 3 daily occurrences.
Manual reset thereafter.
Reading from OAT
sensor must drop 5 F
(2.8 C) before restart


And these are the possible causes:

Faulty transducer, low/
restricted condenser
airflow, low refrigerant charge,
faulty EXV

[GT Jets]

How is this possible on a 30RAP106. The IOM says it could!

This is what it says:

T126 Alert Circuit A High
Head Pressure
Compressor operation outside
of operating envelope. Circuit shut down
Automatic, only after
first 3 daily occurrences.
Manual reset thereafter.
Reading from OAT
sensor must drop 5 F
(2.8 C) before restart


And these are the possible causes:

Faulty transducer, low/
restricted condenser
airflow, low refrigerant charge,
faulty EXV

Think about it for a minute.....

Makes perfect sense to me. What would happen if you had just enough refrigerant to keep the system from dropping out the low pressure switch. No condensing, no cooling, no cooling the pressure just goes higher and higher to to heat build up.

GT

[KB Cool]

Think about it for a minute.....

Makes perfect sense to me. What would happen if you had just enough refrigerant to keep the system from dropping out the low pressure switch. No condensing, no cooling, no cooling the pressure just goes higher and higher to to heat build up.

GT


Have you seen it?

[Tech Rob]

I have seen it on an RTAA; not the scenario GT described, but a high pressure trip as a result of low-charge and a hot chilled water loop. The condenser fans on the RTAA are staged based on system delta T converted to delta P. Low charge = low differential pressure = no condenser fan action = high pressure trip

[KB Cool]

On this particular machine! Would you expect to see a temp. drop across the Liquid line dryer, if undercharged? I got a 12 degree drop across it and sight glass is flashing. Could the temp. drop be because the dryer is so close to the EXV. And again the T126 lockout boggled me. I'm thinking dryers plugged. Now i'm not sure?:confused:

[Tech Rob]

I have never seen this chiller, but I would say that any liquid line drier that is dropping 12 degrees is a problem. How close are we talking? Close enough to the EXV where the condensation from the valve body is affecting your temperature readings? I would think that 8-12" would be enough distance to get a reliable reading.

I would expect to see a temperature drop across a plugged liquid line drier only get worse as the charge is decreased. When you have a low charge, the liquid is closer to the saturation point and will easily flash into a vapor with resistance to flow.

[KB Cool]

I have never seen this chiller, but I would say that any liquid line drier that is dropping 12 degrees is a problem. How close are we talking? Close enough to the EXV where the condensation from the valve body is affecting your temperature readings? I would think that 8-12" would be enough distance to get a reliable reading.

I would expect to see a temperature drop across a plugged liquid line drier only get worse as the charge is decreased. When you have a low charge, the liquid is closer to the saturation point and will easily flash into a vapor with resistance to flow.

The EXV is probally a good 2 feet away!!

[GT Jets]

Have you seen it?


Yes I have, it was a Carrier Aquasnap and it had a low charge and kept tripping the high pressure cut out.

Virtually ANY liquid line drier with the refrigerant at saturation at a high rate of flow (read velocity) due to a high evaporator load and low refrigerant charge will read a higher than expected TD, not sure about 12*F but way more than 2* I think the highest I have seen was 7*F and the drier was fine. Once the system was topped off after a leak repair was made it dropped right back down to less than 1*F

Liquid line driers are designed to filter liquid, not gas, so if the refrigerant is flashing off in the drier, you will see a large temp. drop.

GT

[KB Cool]

Yes I have, it was a Carrier Aquasnap and it had a low charge and kept tripping the high pressure cut out.

Virtually ANY liquid line drier with the refrigerant at saturation at a high rate of flow (read velocity) due to a high evaporator load and low refrigerant charge will read a higher than expected TD, not sure about 12*F but way more than 2* I think the highest I have seen was 7*F and the drier was fine. Once the system was topped off after a leak repair was made it dropped right back down to less than 1*F

Liquid line driers are designed to filter liquid, not gas, so if the refrigerant is flashing off in the drier, you will see a large temp. drop.

GT

That makes sense!! Thanks for the info!

[KB Cool]

Well guys, pulled the charge and cut out of the dryer and i could barely blow through it!!! I'm still baffled by the head trip.

[chilbrig]

If you have Micro Channel Coils, any restriction will cause a high pressure trip. Cut your drier open and see if a magnet will pick up the fiber filter material. If it does, get ready to change out your compressor.

[KB Cool]

If you have Micro Channel Coils, any restriction will cause a high pressure trip. Cut your drier open and see if a magnet will pick up the fiber filter material. If it does, get ready to change out your compressor.

Yeah, it is a Micro channel. But, when i first got to the job. I think my head psi was no where near the tripping point!! But, anyways this what my boss had me do. What a PITA!!! I know the charge amount on the data plate is no longer correct!!:grin2:

[Carrene #2]

Well, I had this alarm. I called for explaination.

The official reason that all those symptons will flag a High Head alarm, "..we're computer programers...picked the five conditions and chose what we thought would be the most common....."......"essentially the compressor is running outside it's design envelope".
Hope that helps. Hahaha

[KB Cool]

Well, I had this alarm. I called for explaination.

The official reason that all those symptons will flag a High Head alarm, "..we're computer programers...picked the five conditions and chose what we thought would be the most common....."......"essentially the compressor is running outside it's design envelope".
Hope that helps. Hahaha

I'm thinking the 650 psi cut out switch flags the alarm!!!No? (transducer)I don't know. If it does it again and that massive filter dryer that i put in isn't clogged. I'm changing the HP switch!!! I've seen a few go bad on RTU's!

[Carrene #2]

I'm thinking the 650 psi cut out switch flags the alarm!!!No? (transducer)I don't know. If it does it again and that massive filter dryer that i put in isn't clogged. I'm changing the HP switch!!! I've seen a few go bad on RTU's!

My problem turned out to be low evap flow. Quite simple actually, just got to check things that would cause the compressor to run, "outside it's design envelope". Hehehe.

Reread your reply, not sure if you understood my post. There's a reason my handle is Carrene and a reason I posted, "official".

Good luck.

[KB Cool]

And whats up with the digital scroll? This peice of SH!t starts unloading every 7 seconds or so and loads again as i get to set-point! It can't be good for it!:grin2:

[Dallas Duster]

Just because it says it digital is kinda misleading. It wouldn't be good for it if it unloaded more than 7 seconds. It works thou.


And whats up with the digital scroll? This peice of SH!t starts unloading every 7 seconds or so and loads again as i get to set-point! It can't be good for it!:grin2:

[Carrene #2]

Unloading a compressor, not good. Go figure.
I think ya could stand to do some reading.
The "POS" compressor is usually misapplied, maintained by someone without the proper knowledge, or something else wrong with the system has caused the failure. Figure it out, that's our job.

[Carrene #2]

And whats up with the digital scroll? This peice of SH!t starts unloading every 7 seconds or so and loads again as i get to set-point! It can't be good for it!:grin2:

Unloading is certainly better than stopping and starting. Do you know of any other systems that unload, rather than starting and stopping ?

I'm beginning to understand how post counters rack up.

[KB Cool]

Unloading a compressor, not good. Go figure.
I think ya could stand to do some reading.
The "POS" compressor is usually misapplied, maintained by someone without the proper knowledge, or something else wrong with the system has caused the failure. Figure it out, that's our job.

Well lets hear it!!! You obviously work on them alot!!! I can honestly say! I don't!! SH to low causing floodback!!! Moisture because of POE!! Liquid off cycle migration due to no CCH!!!m I'm here to learn!

[KB Cool]

Unloading is certainly better than stopping and starting. Do you know of any other systems that unload, rather than starting and stopping ?

I'm beginning to understand how post counters rack up.

Maybe i'm used to the residential thing! The compressors stays unloaded in 1st stage and doesnt go to second every few seconds!!!

[Carrene #2]

Well lets hear it!!! You obviously work on them alot!!! I can honestly say! I don't!! SH to low causing floodback!!! Moisture because of POE!! Liquid off cycle migration due to no CCH!!!m I'm here to learn!

Funny thing is, I don't.
That's why I called Tech Support, looking for clarification on that particular alarm.

I do know how a refrigeration sytem works, I do know how a compressor works, I do know what's bad for a compressor.
Do you?

I have no idea what you know, so I'm not about to peck out over 30 years of experience, just so you might find your answer to the problem.

For your problem, as originally posted, if you understand the term of "compressor envelope" you will know where to look.

I hope.

[KB Cool]

Funny thing is, I don't.
That's why I called I called Tech Support.

I do know how a refrigeration sytem works, I do know how a compressor works, I do know what's bad for a compressor.
Do you?

Yeah, i know starting and stopping isn't good!!!

[Dallas Duster]

The reason it doesn't stay unloaded is for oil return . You could always tell the unit it's not digital and it will just cycle on and off.


Maybe i'm used to the residential thing! The compressors stays unloaded in 1st stage and doesnt go to second every few seconds!!!

[KB Cool]

The reason it doesn't stay unloaded is for oil return . You could always tell the unit it's not digital and it will just cycle on and off.

Thanks dallas!!! WHy didn't carrier just use 2 five ton scrolls and stage them!!! I could probally buy and replace a 5 ton 5 times for what this ten ton digital is going to cost!:grin2:

[Carrene #2]

Thanks dallas!!! WHy didn't carrier just use 2 five ton scrolls and stage them!!! I could probally buy and replace a 5 ton 5 times for what this ten ton digital is going to cost!:grin2:

Did you actually read my posts.
They did include "Misapplied". Hehehe.

[Dallas Duster]

Thanks dallas!!! WHy didn't carrier just use 2 five ton scrolls and stage them!!! I could probally buy and replace a 5 ton 5 times for what this ten ton digital is going to cost!:grin2:

Size matters not sure there is enough room to stick 2 compressors in there for the foot print of the unit I agree with #2 sometimes chillers are oversized. Since most copeland tandems come as a complete unit cost cancels out. Dealing with smaller chillers like that most of the jobs are not professionally engineered it more of a rough guestimate.

[KB Cool]

Did you actually read my posts.
They did include "Misapplied". Hehehe.

Well, i do know these guys added a secondary loop and tried to run the machine through 1" pipe. It was short cycling like crazy.

[Carrene #2]

Well, i do know these guys added a secondary loop and tried to run the machine through 1" pipe. It was short cycling like crazy.

No Kidding.
Who commissioned it?

[KB Cool]

No Kidding.
Who commissioned it?

Nobody commisioned that!! They called and asked why it was turning off and on all the time!!!:grin2:

[Carrene #2]

Nobody commisioned that!! They called and asked why it was turning off and on all the time!!!:grin2:

Just got one like that! Misapplied!

[KB Cool]

Just got one like that! Misapplied!

Well, the customer knew they could not possibly run a 10 ten system on 1" pipe. But, they did think the unit was a true varible speed "digital" scroll and it would be ok ! Serious!!!

P.S. I just saw your edit a little bit ago!! I'll tell them to call you next time!!:grin2:

[Carrene #2]

Well, the customer knew they could not possibly run a 10 ten system on 1" pipe. But, they did think the unit was a true varible speed "digital" scroll and it would be ok ! Serious!!!

P.S. I just saw your edit a little bit ago!! I'll tell them to call you next time!!:grin2:

Thanks, but no thanks. :cheers:

[chilbrig]

With the Micro coils the head will spike at startup then come back down to normal operating conditions. On a hot day it should not spike much over five hundred psig. If you must weigh in the charge subtact about five percent of what it says on the tag. If you overcharge just a little, it will trip. There should be a charging procedure in the OM book, that is the best way to charge it up. Again, if you have any restriction in the drier you will have problems.

[Dallas Duster]

He might be ok charging it up now since he added a small receiver to the system.



With the Micro coils the head will spike at startup then come back down to normal operating conditions. On a hot day it should not spike much over five hundred psig. If you must weigh in the charge subtact about five percent of what it says on the tag. If you overcharge just a little, it will trip. There should be a charging procedure in the OM book, that is the best way to charge it up. Again, if you have any restriction in the drier you will have problems.

[KB Cool]

With the Micro coils the head will spike at startup then come back down to normal operating conditions. On a hot day it should not spike much over five hundred psig. If you must weigh in the charge subtact about five percent of what it says on the tag. If you overcharge just a little, it will trip. There should be a charging procedure in the OM book, that is the best way to charge it up. Again, if you have any restriction in the drier you will have problems.


Yeah i blocked off the condensor to 120° CST and gave it 18° SC.

[KB Cool]

He might be ok charging it up now since he added a small receiver to the system.

I know i didn't want to add the dryer. Would have been much easier just to go back in w/ the 165s. But, my Boss talked the owner into doing the replacable core as thier maintenace men will be able to replace it on the fly as needed!!!

[KB Cool]

Thanks, but no thanks. :cheers:

What a D!ck!!!:grin2:




Nah, he aint a bad guy afterall!! Thanks for the 33% tip Carrene. Well definetly look into it if this compressor decides to lock up!!!

[Dallas Duster]

I guess the boss wins over common sense what is there a whopping 9 pounds or refrigerant in that machine.


I know i didn't want to add the dryer. Would have been much easier just to go back in w/ the 165s. But, my Boss talked the owner into doing the replacable core as thier maintenace men will be able to replace it on the fly as needed!!!

[KB Cool]

I guess the boss wins over common sense what is there a whopping 9 pounds or refrigerant in that machine.

8.6 lbs. There's about eleven in it now!!!!

[rscamaro]

Yeah i blocked off the condensor to 120° CST and gave it 18° SC.

Too much subcooling for a 410a unit with microchannel coils.

...Ron

[supertek65]

Sometimes EEV controls condenser fans.

This could do it.

[KB Cool]

Too much subcooling for a 410a unit with microchannel coils.

...Ron

Why? IOM says 15°-17°. I figured 1 degree over aint gonna matter.

[AiResearch]

The digital scroll is actually a cool
device. It allows a greater range of capacity control than traditional unloaders on a recip.

It is designed to load / unload frequently to deliver a specific output. 40% load time = 40% capacity. Better load matching.

Most units are sized for peak load and run there a small percentage of time. So you have an oversized 10 ton scroll cycling on and off. Over and over. Hard on the compressor for sure. This compressor can stay running and stay healthy.

Oil management with these is a whole different topic.

[Carrene #2]

Why? IOM says 15°-17°. I figured 1 degree over aint gonna matter.

Damn, I swore to myself that I was done with this.
I'm weak.

Do the words "critical charge" ring a bell?

Best of Luck :

Dick :grin2:

[KB Cool]

Damn, I swore to myself that I was done with this.
I'm weak.

Do the words "critical charge" ring a bell?

Best of Luck :

Dick :grin2:

Come on! Who's to say my thermocoupler aint off by 2 degrees!!!:grin2:

[rscamaro]

Come on! Who's to say my thermocoupler aint off by 2 degrees!!!:grin2:

With the microchannel coils I pretty much always go to the low side, and I don't think 15-17 degrees SC is correct for the microchannel unit, I may be wrong but I don't think so. Sounds right for the standard copper/aluminum coils though.

If you haven't seen just what the MC coils look like, you really need to take a look. What you have is pretty much a 1"x 1/8" flat piece of aluminum with say 10 to 15 capillary tubes running the length of the aluminum bar. They don't hold very much refrigerant in them. It is very easy to trip the HP switch with even a slight overcharge.

...Ron

[KB Cool]

Ok i'll keep that in mine if i have to go back!! I figured i couldn't go wrong by following the manual's charging instructions!

[Dallas Duster]

You do what ever you want to it It's the customers machine and he can pay you to make any modifications to it that he wants. For all I care you can put a TXV on it and go with it.



Ok i'll keep that in mine if i have to go back!! I figured i couldn't go wrong by following the manual's charging instructions!

[ckartson]

Carrene #2 you made the most sense. I figured a plugged drier but couldn't figure high pressure trips. I also assumed a pressure switch not a DDC controller. I am not familiar with the equpment being described. Was this an actual pressure switch shutting the comp down or a program in the controller? What brand?

[KB Cool]

You do what ever you want to it It's the customers machine and he can pay you to make any modifications to it that he wants. For all I care you can put a TXV on it and go with it.

Yeah, it'll be a good learning experience!!!:eek: