High Pressure Fault

[AndyHX]

I was asked today to look at a system that is going out on hp. I had not seen system before and unsure about any previous work or problems that may of existed.
i reset the hp and unit runs for about half an hour , pressure gradually rises and trips at 300 psi , system is r22 .
Room is a chiller at 2 c .
Suction pressure 32 psi ,
suction temp at compressor 17 c
high pressure 230 psi 45c
air on condenser 21c
air off condenser 31 - 32c
subcooling 2k
discharge temp 78

compressor is a belt driven
condenser is above compressor
sight glass is not full but do not want to add any refrigerant to system.
Could there be a restriction in system , like the non return valve not fully opening ??
Condenser has been cleaned and both fans are working .
thanks for any advice.

[Tesla]

Firstly we will rule out the compressor as no HP faults result from there. There could be two faults as a possibility. To check for a restriction in the liquid line and an overcharge of refrigerant.

[Brian_UK]

Suction pressure of 32psi = -12°C
Suction temperature of +17°C
Suction superheat of 29°K - somewhat large for the system.

Check the expansion valve, evaporator for correct refrigerant/water flow rates/blockages.

[mikeref]

AndyHX, any chance the condenser fins are corroded or ambient airflow recirculating? Are condenser fans throwing air out from the sides instead of straight up?.. Mike.

[intelligence]

Over charge of refrigerant, dirty condenser, air in system, restricted line on the high side, restricted dehidrator, wrong refrigerant. Be carefull with the new substitute gas to R22 it could be the R422A or R422D. And it could be to the compressor valve plate broken. You have to go step by step from easyest to hardest until you get a conclusion. Good luck

[AndyHX]

Ok , been back today thinking it could be nrv in discharge not opening , removed and checked it seems ok.
Recently txv have been changed as they were r12 which was original refrigerant but still running on r22, the system had been operating like this for years apparently with little or no problems. when the valves were changed hp problem springs up.
If the orifice is over sized , could this overload compressor ? it is what im thinking at moment. Not sure how they were sized to system.
The evaps are very old , impossible to get Kw info about them.
Also compressor is a JE Hall belt driven but with not sure about this capacity either , has any one any info for theses please?
Electric motor is running just over 1 amp above rated amps before trip out.
Sight glass not full .

Mikeref , fans are under horizontal condenser and suck air down and through coil. **** design . getting 10 to 11 c td so i think condenser is doing its best.

Brian uk , yes alot of super heat , but no insulation on 20 metres 2 1/8 pipe out side, and not a full charge in sight glass yet



thanks for all comments

[Gary]

Hmmm... I'm thinking if refrigerant were added to clear the sightglass and bring down the superheat, then the head pressure would skyrocket... which would mean the compressor is, in effect, too much for the condenser.

I'm wondering if the compressor speed has been increased beyond the capacity of the condenser?

[mad fridgie]

If this had R12 valves on a R22, then the valve would prematurly close down, low suction pressures, or lower than you have now, by replacing to R22 valves you are now get a more balanced flow (for the expansion valve)
The system was designed for R12, changing to R22 will dramatically increase duty for the same hourly swept volume, hense lack of condensing duty.
Slow compressor down or fit an CPR, if you want to continue with R22.

[AndyHX]

hey all , thanks for replys . If i were to down size orifice how would this effect the load through the system and evaporator performance , icing up etc? Im really looking for cheapest solution for this job, thanks Andy

[Gary]

Downsizing the orifice would increase the superheat.

The cheapest and best solution is to slow the compressor. It's just a matter of downsizing the drive pulley.

[AndyHX]

Gary , i quess the next question is how do we accurately reduce the speed , how to calculate the required revs ? Take the ratio we now have and slow by a percentage?

[mikeref]

Sounds like you got someone elses headache. Is it possible to change refrigerant back to R12 alternative, like R134a without major system alterations?

[AndyHX]

Yeah , well the valves have just been changed to r22 items , so looking to keep on that track at the moment. With 134a it would be valves , oil and refrigerant, not sure if you think that is major or not, customer probably will.

[NACS]

I like the sound of slowing down the compressor. Either that or I'll try to track down the old R12 TXVs and re-fit them.

[Gary]

Gary , i quess the next question is how do we accurately reduce the speed , how to calculate the required revs ? Take the ratio we now have and slow by a percentage?

I know there is a formula for this, but I haven't been able to find it. :(

Being a hands-on kinda guy, I would get a variable pulley and adjust it to get the cond TD where I want it... then get a fixed pulley that size. Variable pulleys are okay, but fixed pulleys last longer... harder steel.

[NACS]

The R12 TXV's were CHE3 / CFE-3-C.
The R22 orifice is No:5

[NACS]

The R12 TXV's were CHE3 / CFE-3-C.
The R22 orifice is No:5


CORRECTION: The R12 TXV's were CFE3 / CFE-3-C.
The R22 orifice is No:5

[Magoo]

If system converstion from R-12 to R-22 was the condenser upgraded for additional performance and system pressures. Sounds to me that didn't occurr and system is undercondensing hence sightglass indicating low on gas, suction suerheat high.

[NACS]

(note: this is my headache that AndyHX has been trying to help me with)
No the condenser was not upgraded.

[Gary]

Condenser undercapacity for the compressor or compressor overcapacity for the condenser is the same thing as far as system balance is concerned.

If extra performance is needed then upsizing the condenser is the way to go.

If extra performance is not needed then slowing the compressor is the way to go.

[Magoo]

NACS.
Get on with it and up-grade condenser, hopefully the compressor is compatible as well with increase in capacity. Highly unlikely though.
Next is the power supply and protection, oil and yardy yardy, you and your mate have created the situation and now is time to sort it out and have a happy camper client. get on with it.

[mad fridgie]

Has it got unloading heads, if so and really on the cheap, fit hp switch to head unload valve, When SCT is high unload.
I would say your client has had his money worth out of this gear!!!

[AndyHX]

Yeah , thanks Magoo , we are looking for the appropriate solution , that is why the expansion valves were changed in first place , it would be easy to put old valves back in and just leave it , but i would like to see a better performing system. We also have budget to think about.
Thanks for your advice every one.

Mad , the compressor has one unloader head , but not in use , not sure of condition of this.

[mad fridgie]

Yeah , thanks Magoo , we are looking for the appropriate solution , that is why the expansion valves were changed in first place , it would be easy to put old valves back in and just leave it , but i would like to see a better performing system. We also have budget to think about.
Thanks for your advice every one.

Mad , the compressor has one unloader head , but not in use , not sure of condition of this.
Lets reverse the question, how much is the budget?
You would like a better performing system, but does your client care, if it is going to cost him money?
When it ran with the old valves on, was the client happy with its duty? Has he changed is duty requirement want more cooling.
is it personal pride that wants to make the system better? (not a bad thing)
If originally R12 and hall recip comp then is very old, sounds like an ex apple and pear board store!

[NACS]

NACS.
Get on with it and up-grade condenser, hopefully the compressor is compatible as well with increase in capacity. Highly unlikely though.
Next is the power supply and protection, oil and yardy yardy, you and your mate have created the situation and now is time to sort it out and have a happy camper client. get on with it.

To be fair this is not a situation of our creation. I've inherited a problem site and am trying to work my way through the previous contractors issues. AndyHX is only trying to help me out. Please don't tar him with this dirty brush.

This is the story so far; I was called to the site due to the system not running. When I arrived I found both belts broken and no refrigerant in the system. The on site engineer can't even tell me how long the unit hasn't been running for. There is a second system (R134a) running in the same chiller that has been carrying the load through winter. Because this is a belt drive compressor with auto reset on the LP, the evap and condenser fans had kept running. It wasn't until the load went up that the second system couldn't hold temp. I replaced the belts and found a bad leak at a TXV. At this point I noticed the system was running R22 with R12 TXVs. I discussed it with the site engineer and he told me this system had been changed onto R22 some years prior. I decided to change the TXVs to R22. I took the R12 TXVs to my refrigeration wholesaler and he cross matched them for me.

[Gary]

Has it got unloading heads, if so and really on the cheap, fit hp switch to head unload valve, When SCT is high unload.


This might be the cheapest and easiest solution yet... if the unloader works.

[mad fridgie]

To be fair this is not a situation of our creation. I've inherited a problem site and am trying to work my way through the previous contractors issues. AndyHX is only trying to help me out. Please don't tar him with this dirty brush.

This is the story so far; I was called to the site due to the system not running. When I arrived I found both belts broken and no refrigerant in the system. The on site engineer can't even tell me how long the unit hasn't been running for. There is a second system (R134a) running in the same chiller that has been carrying the load through winter. Because this is a belt drive compressor with auto reset on the LP, the evap and condenser fans had kept running. It wasn't until the load went up that the second system couldn't hold temp. I replaced the belts and found a bad leak at a TXV. At this point I noticed the system was running R22 with R12 TXVs. I discussed it with the site engineer and he told me this system had been changed onto R22 some years prior. I decided to change the TXVs to R22. I took the R12 TXVs to my refrigeration wholesaler and he cross matched them for me.

Firstly cross referencing the expansions valves does not equate to cross referencing the system. OK your evap duty will balance bigger TD on R22 , but your problem is that your condensor/moter can not handle the new upgraded duty. Your new valves are starving the coil as to be expected. hence high superheat. (I also suspect that with the R12 valves this has always been the case, no even more stavation and lower suction pressures, less heat of rejection for the condensor)
Your options are
1; Reduce refrigerant mass flow (speed, suction valves or unload)
2; increase condensing and evap capacities to to meet compressor swept volume.
3 scrap it, send it Wellington "Te Rapa" as an antique and install some new gear

[Magoo]

Hi NACS,
my error replace "created with Inherited ".

[mikeref]

Yeah , thanks Magoo , we are looking for the appropriate solution , that is why the expansion valves were changed in first place , it would be easy to put old valves back in and just leave it , but i would like to see a better performing system. We also have budget to think about.
Thanks for your advice every one.

Mad , the compressor has one unloader head , but not in use , not sure of condition of this.
AndyHX and NACS, time to confront the owner and explain this situation. I've done this on many occasions to very difficult clients who refuse to part with their cash. Heard it all before. (Been working for ? years and the last guy did whatever at 0 cost). However, cheapest solution is to slow compressor down as Gary has said. New client could be thinking your taking him for a ride so post motor and compressor pulley sizes and motor speed, (guessing 1440) .. Mike

[mikeref]

Hi NACS,
my error replace "created with Inherited ".
So true and now a learning curve. How to instill confidence in your client or unfortunately resort to band-aid method untill they see the colour of money.. Mike.

[NACS]

Unloader has sorted the problem. Cheap easy fix. Thanks for your help.

[mad fridgie]

Unloader has sorted the problem. Cheap easy fix. Thanks for your help.
Your are welcome
"Buy a Boost Unit" !!!!!!!!!

[AndyHX]

Yes , thank you MF .
I have a few Mahanas that keep having problems , so when there is next problem , i will be in touch !