View Full Version : is 305/80 psi normal for r-22 carrier unit?
07-13-2005, 02:44 PM
I am new to this forum.
I have had training in a/c, but have used that training mostly in enviornmental chambers that use a cascade system, and where the ambient temp is stable. The typical prssures for the R-22 in those units is 200/20, and is "cooling" the other system (R13 or R23)
This is my first building a/c refrigerant(possibly) related problem I've had.
Yesterday, this paticular unit shut down from what I am suspecting to be an High pressure condition.
I connected the gauge set, and purged the hoses from the other freon that was in them, thus releasing some pressure.
The unit restarted, and ran. The pressure's were at 86/345
with an outside temp of 92 and a high load inside.
I checked out another unit that is the same model number as this one (carrier 38AE-012) this morning, and it runs at 215/70 at the same time the unit in question was running at 305/80. With outside temp being 83 and RH 33%. Inside temp for both location were 74.0 and 47%RH. Both units are on the shadey North side of the same building. The unit in question does have a higher load than the other. It has not had any service work done to it for at least 4 years.
I was wondering if it had non condenseables, but with the lack of recent service, and assuming that this system does not go into a vaccum, and no leaks detected so far, I am guesing that there would not be a way for NC's to be introduced into the system.
There are a lot of bubbles in the site glass too.
I hope that I have provided enough usefull information to help me with this.
I would appreciate any suggestions!
[Edited by drycold on 07-13-2005 at 03:06 PM]
07-13-2005, 05:25 PM
07-13-2005, 05:36 PM
pressures dont mean a thing. whats the subcooling and the superheat. now if you want a lot of answeres then pressures will give you that but the correct answere will come from
subcooling and superheat.
i would first clean condenser coils. then get subcooling and superheat and well tell you if theres any other problems
07-13-2005, 05:53 PM
The condenser has not been cleaned with chemicals this year.
But it is not that dirty looking, that is it is not blocked by any debris or plugged up with dirt. But it is not shinny clean by any means.
I will clean it very well tomarrow, and then check the superheat and subcool. I have had a very difficult time trying to get the temp probes to get accurate readings on the piping. Do the infared gun type thermomters work very well for this? If they do, this would be a great time for me to get one. I guess it would be difficult to take readings with that type with the panel in place though. Are there any good tricks to get the temp probes to stay in good contact with the pipe? This has been a big pain for me in the past.
I am so greatful for people who are willing to share there knowlege with other people. God bless you all!
07-13-2005, 07:51 PM
You have to mentally shift gears when you go from a refrigeration application to air conditioning equipment. Yes, they both use similar means to effect refrigeration, but the particular things you run into when servicing these systems are a different animal, as you're now learning.
An a/c condenser coil can appear clean on the surface but be dirty further in. If it is a double row coil (one coil with two runs that can be separated for cleaning), the scenario of being clean on the surface yet possibly packed with filth within goes double, pardon the pun.
As for your temperature probe, invest in a pipe clamp type k thermocouple and don't look back. It's the best way to go when you're going for superheat and subcooling readings. Failing that, a regular type k thermocouple (the thin yellow ones) can be taped to a line with electrical tape, but I don't find that nearly as handy as a pipe clamp thermocouple. Both Fluke and Fieldpiece make these clamps, as well as other makers.
Originally posted by Freezeking2000
Don't need superheat and sub-cooling to figure that one out
07-13-2005, 08:19 PM
Carrier 38AE012 is definately a double row condenser that has to be seperated to clean and the horse shoe shape makes it loads of fun.
07-14-2005, 09:30 AM
Thank you all for the advice. I will dig in and let you all know.
...and after you pick up the miles of hose you ran on the roof don't forget to check the refrigerant charge.
07-14-2005, 01:41 PM
First and foremost, let me be the first to welcome you to this HVAC/R forum friend.
Second, of all you have not posted all the required readings to properly and accurately diagnose this system. You have raised our suspicions that this system does have a dirty condensing coil as Freezeking2000 has already posted based on the limited information you have provided this thread.
Given the fact that this particular unit has not had any “service work”, which may or may not include P/Ming, in at least the last four years would suggest that you first clean the entire unit including the evaporative and especially the condensing coil and then obtain a complete set of operating readings to ensure that this system is operating correctly, and at full capacity.
After the unit cleaning, restart the unit under a load that insures that the Carrier #O6DS328 compressor is loaded up, and that both condensing fan motors are operating, and then obtain as many of the following operating readings as you can after letting the unit operate for at least five minutes:
Liquid line pressure
Suction line pressure
Compressor FLA or RLA
Compressor actual operational amps
Return air dry and wet bulb temperatures
Supply air dry bulb temperature
Suction line temperature
Liquid line temperature
Return static pressure
Supply static pressure
After you obtain these readings, post them on this thread and we will analyze them for you and determine how well this unit is operating.
John J. Dalton
07-14-2005, 03:04 PM
freezeking and sonc were right.
The condenser looked great until I got the two half’s separated to see all the cottonwood seed and crap in there.
I am a Maintenance Mechanic for the company I work for, and we do an annual PM on all of our systems including evaporator coil and the condensing unit. So, I have cleaned this unit every year, but I have never separated the rows to clean between them. 4 hours and a pair of soggy shoes latter, it is clean.
I have 1 of 7 done now! And only 8 roof top units after that.
I am planning on doing a "baseline" for every unit we have after I have cleaned them.
Mr. Dalton, I very much appreciate your input on the information needed to help with troubleshooting refrigeration. However, I am unfamiliar with "OSA". Is it Outside air temp?
And, with these split units, there are solenoids that maintain a pressure on the supply line, so is the static pressure measurement needed on the return and supply? Also, this unit only has 2 ports for the gauge set to connect to.
one on the supply line and one on the return line. there is however a plug installed on the discharge service valve on the compressor that I could install a schraeder valve
into. Would those 3 pressures work? Would RH% work or should I convert the dry bulb temp and RH to a wet bulb temp? Should all this info be included in the baseline that I am preparing to do?
I need to get a pipe clamp thermocouple before I will be able to finish this project. I live in a small town without a refrigeration supply shop, so I will need to order it.
Thank you to everyone for not making me feel like the rookie that I am.
07-14-2005, 04:34 PM
Regarding your previous post:
“…Mr. Dalton, I very much appreciate your input on the information needed to help with troubleshooting refrigeration. However, I am unfamiliar with "OSA". Is it Outside air temp?...”
”…And, with these split units, there are solenoids that maintain a pressure on the supply line,…”
These “solenoids” are more than likely liquid line solenoids, whose function in life is to shut off the liquid refrigerant flow to the air handler(indoor section) and often work in conjunction with another device located inside the condensing unit(outside unit) called an automatic low pressure switch. On a call for cooling from the room’s thermostat, power is supplied to the liquid line solenoid and refrigerant starts to flow thru the evaporative coil(inside coil) and continues back to the condensing unit where the automatic low pressure switch begins to sense an increase of suction pressure, it finally increases to a predetermined point as defined on the “cut in” of the automatic pressure switch and turns on the system’s compressor and condensing fan(s) and the system starts to cool. When the room’s thermostat reaches setpoint(the temperature for which it is set to maintain), it terminates power to the liquid line solenoid and the liquid refrigerant flow is stopped. This causes the suction line pressure to drop(commonly referred to as pump down), it finally drops to a predetermined point as defined on the “cutout” of the automatic low pressure switch, and the system once again cycles off the system’s compressor and condensing fan(s).
“…so is the static pressure measurement needed on the return and supply?...”
This refers to the static pressure measurements of the return and supply plenums(air ducting connections) located on the air handler(inside unit) and needs to be measured with a manometer(an instrument that measures very low air pressures, usually in inches of water column, 27.72 inches of water column equals 1 PSI)).
“…Also, this unit only has 2 ports for the gauge set to connect to. one on the supply line and one on the return line. there is however a plug installed on the discharge service valve on the compressor that I could install a schraeder valve into. Would those 3 pressures work?...”
The two ports you are referring to are called the suction pressure(larger pipe that is usually insulated) and the liquid pressure(smaller pipe), the plug on the discharge service valve, if an access valve was installed, would give you the discharge pressure.
“…Would RH% work or should I convert the dry bulb temp and RH to a wet bulb temp?...”
In regards to dry bulb, wet bulb, and relative humidity measurements, obtaining any two measurements will give you the third one so any combination of two of theses are satisfactory for our needs.
“…Should all this info be included in the baseline that I am preparing to do?...”
If you would like to determine a true baseline of how this equipment is performing, then the answer would be yes. But admittingly, most Maintenance Mechanic’s never do this for a variety of reasons, insufficient time, haven’t got the tools, instruments, knowledge, don’t care, ect.
“…Thank you to everyone for not making me feel like the rookie that I am.”
I think you’ll find that most of us here at this forum still considers ourselves “students” in our craft, and as such, will answer almost any question you could think of with the respect due a fellow peer or colleague.
Hope this helps friend, and keep posting.
John J. Dalton
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