High head pressure , high sub cooling.

[Drew]

Hey all,

I've been working on a system that tripped on hp on a warm day. The head pressure looked high for the conditions but liquid line was cool and sight glass full.
fitted gauges and found hp to be 52c /r404a. The liquid line measured 30c. Ambient 28c. Therefore perceived sub cooling 22c.
I thought the system might be overcharged and started reclaiming, but soon noticed flash gas in sight glass. The liquid line had only dropped 1c to 29c. Considering the hp was still at 50c would this confirm non condensables?
If I have brought the sight glass to the point of flashing I would assume the refrigerant to be saturated. If the refrigerant is saturated I should be abled to obtain the relevant pressure . If the pressure reads to be higher, then there are non condensables.?

The refrigerant can still condense and the system might still seem ok , but the hp will be higher than expected and a standing pressure temp test should be done, but does the test that I did confirm non condensables in system.?

thanks

[Coorsman777]

I am going to answer your question with a question.

Wouldn't non-condensables in a system always show as bubbles in the SG. Because by definition a non condensable should always be in a vapor state.

I have never had a system with non condensables in it so I am curious.

[passandscore]

Non-condensables are certainly an option.

Non-condensables tend to hangout in the condenser displacing it's surface area and decreasing its ability to transfer heat. Until removed, the non-condensables will remain a vapor in the condenser and not flow to the outlet as a liquid refrigerant does.

See link to answer your question: "does the test that I did confirm non condensables in system?"
http://www.refrigerants.com/pdf/NRInews-Smr11.pdf

If you are going to reclaim, purge from the vapor port of the cylinder and recharge with the same gas, be sure that the temperature of the bottle and pressure of the gas correlate properly to the figures on a PT chart. If not, charge with new gas as yours may have fractionized.

[Magoo]

The system should operate with a clear sight glass approximate to design conditions, way above that the liquid line sight glass will bubble its nuts off. Check the circulated flow rate for refrigerant for the higher conditions. with system overcharge at low ambients can risk hydraulic conditions with liquid stacking and safety relief outages.

[Drew]

Thanks guys, recovered the refrigerant/nitrogen mix, vacuumed system , recharged , hp much better , sub cooling good. Suspect this unit had a bit of nitro since the instal 3 years ago. Suspect installer vact out lp side with sol de energised isolating hp side with nitro still charged. We can get away with that in hobart as temps rarely get hot and most of our condensers are sized for mainland conditions.
I pumped system down , ran condenser fans for a while , watched pressure drop and become stable on the hp side. Ambient 30c , hp at 45c on temp pressure chart, this would be the combination pressure of the nitro and the refrigerant when if it was just the refrigerant it should be at 30 c (saturated) Confirming the nitro because I would think air would have burnt out the system a while ago.
good idea about purging the nitro out of the refrigerant passandscore according to the pt chart.
and yes your refrigerant can condense and sight glass will act ok, because the nitro will sit at top of condenser and receiver and not influence the operation other than high hp and innefeciency.

[Drew]

I've never seen one with such obvious pressure difference either coorsman777 I think, but we wouldn't really know I suppose because most comps would fail in time , we would recover , replace , recharge and all would look ok. Walk away. I have seen vrv systems that haven't been been vact out properly and after a few years compressors stated making a high pitched noise and eventually failed , lost maybe 6 compressors on different units on this one site before daikin diagnosed copper plating on the wearing surfaces due to moisture . The photos they sent us belong in a manual. Exactly like it is explained. Such obvious copper plating on just the hot surfaces. Hard to deny... The surfaces become proud due to the copper and bearings start screaming. Never noticed the pressure differences on the vrv cause they manage their own pressures by ramping up and down etc...but was probably not running very efficiently.

[Coorsman777]

Thanks for the response and the explanation.

[Drew]

I'm busy with a similar weird pressure issue and I'm wondering whether it's the same fault as above with regard to nitro in the system.
The unit I'm now working on is a split ducted running on r22. It is very basic mechanically with only a capillary tube as it's expansion device and with a reversing valve operates in heat or cool.
Found the system with low head and suction , suspected gas leak, found small leak on flare nut , tightened, checked and started to charge up the system using super heat , sub cooling and gauges to get the charge right. After adding what I thought should have been enough the superheat seemed ok , sub cooling seemed quite high, head pressure was ok, but suction was low at -5c . Even with the super heat seeming ok the compressor was sweating?
Also the head pressure would drop from 45c to 35 c quickly, the suction would then follow from -5 to -8c, with a climbing superheat then both pressures would climb again. Considering there are no variable speed components this is weird. The pressures should be stable. Also considering that there are no receivers and that the condenser is not a header type but one pass through could nitrogen being flushed through the system be influencing my pressures in both my suction and head ?

could my head pressure be falsely high due to nitrogen giving me a false sub cooling reading ?
therefore I'm still actually undercharged and getting flash gas at the capillary tube causing the varying pressures and superheat and sub cooling readings?

might be forced to recover and recharge to check.
Finding it hard believe that I could get two nitro issues in two weeks after not seeing this fault once in 22 years.
This compressor was fitted 1year ago , but the varying pressure issue was only noticed now.

[RANGER1]

Drew,
Maybe there is more than one problem.
For what it's worth it might be best to reclaim charge & start again as you say after you vac it out.
If it has correct charge on some nameplate it math help as we'll.
I think indoor unit should be checked , cleaned as well as filter.
Moisture in system could also be possibility so not sure if you can install a filter drier, or vac it out.
System may have run In a vacuum for awhile with low charge of R22?

[Gary]

Also considering that there are no receivers and that the condenser is not a header type but one pass through could nitrogen being flushed through the system be influencing my pressures in both my suction and head ?

This is a reversing system, meaning the nitro (if there is nitro) might be shifted back and forth and thoroughly mixed each time the reversing valve energizes/de-energizes.

[Drew]

Indoor unit is nice and clean, fans up tp speed, diffusers all open etc...
yes, nitro could be moving around due to reverse cycle .
Thanks guys.
there was talk of a ' holding charge ' during the compressor change. And 2 techs did the job.
Could have been that the tech thought the holding charge was r22 but was actually nitro.