high suction pressure

[chillout]

this unit im workin on, charged wit r-22, has a suc pressure of 90 and a head pressure of 245... super heat is 5 degrees and im not sure what the sub cool is cuz it has a water cooled condenser coil and that just threw me off..at first i thought it was undercharged but then i thought well the super heat low and the suc pressure is really high so maybe thats not it....the system has been operating for bout 15 yrs and filters have been changed on time but the evap coil is filthy and has NEVER been cleaned......can a dirty coil cause high suc pressure?

[acjourneyman]

OOPS, your right.High load will cause high suction pressures too.

[Edited by acjourneyman on 07-19-2004 at 12:56 AM]

[Learner]

The only way a dirty coil will cause high suction is if it's the condenser coil that's dirty.

If you want help troubleshooting this problem, we need a lot more info. Get every piece of info you can think of and post it. You should get plenty of offers for help then. We can only guess if we don't know more of what's happening with the system, and if we guess, we may send you down the wrong path.

What kind of unit...package air conditioner, wine cooler, split system heat pump??? What brand, size and/or model#?

return air temp, supply air temp, entering condenser water temp, leaving condenser water temp, receiver?, sight glass?, TXV?, length and diameter of refrigerant lines, refrigerant lines insulated?, do the lines go through a hot attic or through a cold room, etc.

Don't let a water cooled condenser keep you from taking subcooling. Subcooling is nothing other than the amount of temperature difference between the saturated temp of the liquid refrigerant in the condenser, and the measured temp of the liquid line. If 245 psig is the pressure at the liquid line service valve (not the compressor discharge service valve) look at your gauge or PT chart and see what the saturated temp is at that pressure. Then subtract the measured temp of the liquid line from that reading to obtain subcooling.

[caosesvida]

you can also check the td through the water coil for more info.

[maddfridge]

we had this situation with the water chillers we cleaned the coils but still had problems.

Turned out that the condensing fans four in total were not correctly set up on the hp pressure switch used to bring them on fans no2 and 3 were set to close together and quickly bought down the head pressure to quickly

so clean those coils and check the fans to see if they are pressure controlled or varable speed

good luck

a speeding slug is a snail with out a home

[bjefferson]

Originally posted by chillout
this unit im workin on, charged wit r-22, has a suc pressure of 90 and a head pressure of 245... super heat is 5 degrees and im not sure what the sub cool is cuz it has a water cooled condenser coil and that just threw me off..at first i thought it was undercharged but then i thought well the super heat low and the suc pressure is really high so maybe thats not it....the system has been operating for bout 15 yrs and filters have been changed on time but the evap coil is filthy and has NEVER been cleaned......can a dirty coil cause high suc pressure?



What's the load in the space trying to be cooled?What is your compressor amp draw?

[R12rules]

KISS


Clean that evap coil.
Make sure you got the airflow you need across your evap coil.

THEN ..... then take some pressure readings and temps.


What your telling me is you got a 95 degree room. This is from your low side reading.
You hi side reading could be ok. It is a little hi right now, but just look at the load on the system.


Once you get her all cleaned up .... things will change and you can then make a better diagnosis. Right now you cannot do that.

[glgto]

i agree with LEARNER i think people are to quick to give advice without all of the information its tough to give good advice for those of you who think im wrong lets use this problem some one writes ive got 18 deg superheat and 9deg subcooling and my temp split is 4 deg whats wrong? well maybe nothing if its a flower box with a low e coil! you can guess all day but the more info you have the better these people can serve your needs how come nobody lists discharge temp? condenser split what temp unit is ment to maintain? and for heavens sake if a coil is dirty clean it first ! if a condenser cant condense how can you get liquid? this is a big problem in captube systems well im done rambling for now

[chillout]

yea i only work at this hotel part time...that is where the unit is located....i just got my epa so my boss lets me fool around wit the systems to get familiar with them for when i finish school, so any ways yea ill get more info when i go back to work on thurs and ill post it up.. only other thing i can pretty much say is that its a heat pump, package unit stored in the ceiling of a hotel ballroom covered by ceiling tile so its VERY difficult to work on with all the duc work and pipes running around and pretty much theres no space. oh yea and it has capillary tube and the entering water temp for the condenser is 82 degrees F.

thanx guys!

[Learner]

Originally posted by chillout
this unit im workin on, charged wit r-22, has a suc pressure of 90 and a head pressure of 245...

OK, and you have a cap tube system and cond ent wtr temp of 82 degrees. You've just given us some hints as to what's wrong. But don't just accept it at face value. Put your thinking cap on, as much as possible for a new technician beginning to learn the trade.

245 psi on the high side is what temp according to your temperature/pressure P/T chart? I think it's over 115 degrees. Now, that is EXCESSIVE for 82* Cond Ent Wtr Temp. Generally speaking, most water cooled condensers have about a 10 degree split.

OK, now think about this next part...many journeyman haven't figured this one out yet, so get a step ahead of them. You have a cap tube system. A cap tube is a "fixed orifice" type of metering device (not modulating like an expansion valve). With a fixed orifice, the higher the refrigerant pressure entering the metering device, the more refrigerant will be metered through it. Now, if you have more refrigerant going through, and into the evaporator, the LESS superheat you will have, because you are OVERFEEDING if the high side pressure is excessive.

What causes high head pressure??? Things like overcharge of refrigerant (my guess in your case), dirty (fouled) condenser, lack of condenser water flow, air in the system, and probably a few other things.

By the way, high head pressure typically causes high suction pressure, especially on a cap tube (fixed orifice) system.

More information could cause me to modify my advise, however, based on what you've told us, here's my recommendation.

1. Even though this is not the cause of high suction, Clean The Evaporator, because it needs to be clean. If it's dirty, it causes LOW suction pressure, and causes inexperienced techs to overcharge a system.

2. Just for kicks, and for a learning experience, check the system vitals, and record the pressures, water temp entering and leaving the condenser, air temp entering and leaving the evaporator, measure superheat, and subcooling.

3. Make the needed repair: Recover all of the refrigerant (weigh it so you can see how much it was overcharged). Pull a vacuum, and weigh in the correct refrigerant charge per the data tag.

4. Take the system vitals again, recording the temps and pressures, and go to your boss with a smile because you've gained some valuable experience, and you've fixed his equipment.

[airworx]

need subcooling for correct diagnosis. liquid line is a liquid line. water or cooled doesnt matter. 5 degrees is to cold unless this is a flotronic chiller. head pressure on a watercooled unit should not be over 225 or scaling will increase. pull the ends off brush the tubes. pull and clean orfices in tower then clean strainer and tower basin. you should run 10 degrees subcooling and 15 to 20 degrees superheat. unless this is a flotronic. then you would run 29 degrees superheat across windings or 3 to 10 degrees superheat depending on eprom chip. subcooling will depend on exv percent open.

[Learner]

Originally posted by chillout
... its a heat pump, package unit stored in the ceiling of a hotel ballroom covered by ceiling tile ... and it has capillary tube ...

[glgto]

IM BETTING ITS A COAXIAL COIL CANT CLEAN IT THAT WAY

[twcpipes]

Just some cheap advice:

Before you take all the required readings, pull a vacuum on your low side gauge before you start. If there is oil trapped in the gauge the hydraulic pressure will make the gauge read high.

[glgto]

what? how can oil cause this? a bordon tube (the piece in the back of your gauge that makes the needle move ) works strictly on pressure . pressure is pressure! oil or beer in you guage wont make a hill of beans differance in what pressure it reads ! atmospheric pressure is the only thing that could effect it and thats not his problem.

[ericnyc]

clean the evap, back flush condenser if you can, clean the strainer(if there is one). check your pressures.

[twcpipes]

If you want the mechanics of refrigerant gauges call the manufacturer. All I can tell you is the first time it happened to me was 1965 and it has happened a hell of a lot of times in 40 years. I had a couple of very smart start-up men both tell me to do that and I have and it works. Perhaps Mr. Bordin missed a step in his technological
break-through.

[glgto]

well, it goes against the laws of physics and if this were true it would be no differant than a boiler guage it has a fluid behind it if you take it out and put a gas behind it at the same pressure it will read the same. im no rookie either ive been in this feild 17 yrs. im from missouri,
the show me state)really im from pa, but i dont think oil is the problem. try this calibrate you guage, fill your hose with oil, then pressurize the hose, observe the reading .drain all excess oil and repressurize take a reading, evacuate the hose and guage then let it go back to atmosphere. then pressurize with the same pressure i bet all 3 read the same.only possible answer i have for this would be a old guage with a stretched or weak bourdon tube.and it wouldnt be consistant.

[Learner]

Glgto, have you personally done that experiment, or are you just saying that because it sounds logical? I think twcpipes may be correct. I've personally, more than once, experienced something similar, not with gauges, but with low pressure controls.

I've seen supermarket compressors operating in a vacuum because the low pressure control would not shut them off, when the setting was at a positive pressure. I've removed the cap tube from the compressor flare nut, drained the oil from the control's cap tube, reinstalled, and everything worked normal after that.

This is why in some of Robert Shaw's technical literature it is stated to route the low pressure control capillary tube at least 4 inches vertically up, prior to routing the cap tube downward to the control. It is to keep oil out of the tube so the hydraulic pressure won't adversely effect the operation.

It takes awhile for that oil to drain out. The first time I noticed it was after replacing a control, I noticed a puddle of oil under the old control I removed.

[twcpipes]

And when liquid is put on top a reciprocating piston and the piston comes up the pressure against the valves doesn't increase either. It's been all a scam for 70 years by compressor manufacturers to sell replacements. We know now that to be true because of the Laws of Physics. And we also know I have been removing oil from closed refrigerant loop apparatuses for no good reason except it works. I didn't even put all that water in those chilled and hot water lines then add nitrogen to build pressure either during all those start-up years for pressure testing.
One drop of oil blocking a line, then add a varying pressure the highest pressure will exert the highest hydrostatic pressure. I read that somewhere once. I'd go back to the books but I threw them away when I retired.

[glgto]

ill belive the vacuum explaination because you may not be able to overcome the viscosity at whatever vacuum but im having a hard time beliving the positive pressure and ill try this experiment next week and let you know the outcome if time allows you will know ill start a new thread as i said before i don't doubt you ill try any thing once ill also suck it up if im wrong. fair enough?

[freshie_R134A]

hello... big brothers and big sisters...

[rockn_yota]

wow to pulling up an old thread...did anyone ever figure out the real truth to this debate? Now i am curious.