Military A/C Need help
Hey guys. New to the site, and I am in a predicament and don't have time to register properly yet. I have an 8 ton ECU made for the military by YORK, and am having problems no one can figure out.
I just installed a new compressor, and it keeps over heating. I have washed everything out, and my intake pressure is still 43#, and discharge is 165#. The temps in the intake ducts are 75, and the supply duct is 59 degrees.
The condenser inlet was 85, and my electronic program (AC PAL) suggests that the evaporator is too big for the condenser. The compressor is overheating, and the oil level is where it is supposed to be according to Copeland instructions. Am I missing something? I have no idea what is wrong, and all of the upper echelon guys in my maintenance section can't figure out what is going on either. We are pretty much self taught in the Marines, and learn as we go. So any advice is very much appreciated.
Hi jarhead....old army puke here lol.j/k.We need more info to help you.We will need at least the superheat & subcooling temps along with the pressures.Giving the temp in & out of the evap was good do the same for the condenser too.Is this at a remote site running on a generator?Are the hertz right?Voltage ok?Eight tons would be a huge coil if it is a single layer(for most military apps.),does this unit have two rows of coils on the condensor?If so it may be plugged in between the coils,see if they can be seperated to clean between them.....I have worked on alot of that old military cr@p.I used to run the hvac/power generation shop for 413 M.I.B.N.L.I. in soto cano honduras.I got the inscom excellence of maintenance award for 1990(with the help of my great crew).I will be glad to help any way I can.
Take your time & do it right!
Nice to see someone has been where I am at. Although I'm not sure about the Army thing. I went to school in Aberdeen, and saw some questionable characters! LOL I am in kuwait, in the middle of blowing sand country.
Ok, now you are getting into something that they didn't teach me, and I know little about. The condenser inlet temp was 85 at the time. It gets up to 115 during the day. Subheat and supercool temps, these I don't know how to get. They tell us to look at pressures, and don't mention these things. I have been looking, and have a vague idea what they are, but I don't want to give you wrong info.
Yes, the generator is running good, good voltage and hertz. This stuff I know about. Fixed a lot of those. The a/c I have is a new unit (3000 hours). Four row condenser, 4 row evaporator. Built by York. I have blown it out as best I can with an air compressor at 125 psi.
Thanks for the reply,
The Marine hasn't been shown it, the Army guy i might know but hasn't said it, so the AirForce guy will have to teach it. <- LOL ( j/k ). Before I start thanks for protecting all us former vets and these civilian slugs too.
Superheat = the amount of sensible heat added to a vapor above the laten heat of evaporation. You check this by take the evap pressure then look on a PT chart for your refrigerant. convert the pressure to a temp. Then take the outlet suction line temp from the evaperator coil. subtract the first reading from the second. thats your superheat.
Subcooling = the sensible heat removed from a liquid below the laten heat of condensation. take the liquid line pressure at the king valve (if you have one) convert this to a temp. Then take the liquid line temp near the king valve (if you have one ) or near the outlet of the cond. subtract this reading from the first. thats your subcooling.
The readings you are taking are to help you determind if the unit is charge fully. Your compressor uses suction gas to help cool the compressor so if the charge is low your compressor will overheat.
Another RETIRED AF to the rescue!!
once you get the info requested things will be easy for us to help! you might want to post a Model number also, type refrig (should be R22 or 410A). If 22 @ 85 degree amb you should be running around 240 psi on the high side and well 60 to 80 psi on the low side dependant on the indoor condition area, (Temp, Humidity ect..). Also other things that would be good to know, why was the comp replaced, was it the same model, was a vacumm pump used, how about micron gauge! The more the easier for us to help! If you dont have a temp/pressure chart look on the bottom of the Refrigerant box, should be one there!
[Edited by tbk on 10-19-2006 at 07:43 AM]
Another retired AF guy here too. Thanks for your service to our country fellows. I'm trying to remember what brand ECU's we had at Gitmo and Korea. They had hot gas bypass and an evap quench valve if I remember correctly. I liked them better than the older Trane and Keco units.
You need the "Complete" As Built Manual that came with the unit. To see the actual operating parameters. IE I had a chiller for cooling Hydralic oil, they were trying to maintain a 45' glycol temp. so they could cool the oil. It was supposed to maintain an 85' glycol temp. The oil cooler was fouled over the years and they just kept lowering the temperature. Email York if you can't find the manual.
As far as the evap size I wouldnt go that route considering you didnt have a problem before you changed the compressor. What type of refrigerant are you working with?
Well, I know you Air Force junkies know a/c's. I haven't seen a wing unit without it. Guess they can't hang in the real world. ;-)
Ok, I will try to answer all questions
superheat-there is not a port next to the evap. Only on the compressor suction and discharge. Suction-45 psi Discharge-200 psi The temp of the evap. inlet, if that helps (probably not) is 90 before the metering valve, and 54 after. 38 on the backside of evap. The temp of the outlet was 72 (insulated pipe, so kind of hard to get. Insulated with TAR)
Subcool-there is no port or king valve next to the condenser either. There is a reciever, but no port there. SO, the temp. of the supply to condenser was 108. The outlet was 94. Again, not sure if this will help.
TBK-I am using R22, and ambient temp of 82, pressures are 45 and 200. The compressor was replaced be cause it burned out. The evaporator kept freezing up, and the system would go into bypass so long that the compressor would overheat and shut down. I was on gate duty, so I couldn't watch it, and you sure can't depend on someone else to check it for you. That went on for a month, and the compressor started growling and the pressures were fluctuating bad. Then it just stopped. Burned out. Yes, I pulled a vacuum for 72 hours prior to pulling bad comp. Then pulled a 48 hour vacuum after new comp installed. I have no idea what to use a micron gauge on, or even what it does.
I guess that about covers it. Not sure if this will help you, but I learned about superheat and subcooling, so it helped me a lot.
how's the liquid line temp and is there any temp drop out of the LL dryer and was it changed with the burnout
I did replace the drier. The first compressor that went out, the a/c tech that my unit hired to look at it, replaced the drier, saying it was faulty. Two days later, I changed the compressor and drier because he misdiagnosed it. It was freezing the line after the drier, but only because the compressor was coming apart internally and plugged the drier. The temps are within 2 degrees of each other when I use my infrared thermometer.
There is a guy here on this board (NormChris) that is a York factory instructor and he may be able to help you out. You might try to pm him if he doesn't jump in here.
[Edited by tucsonbill on 10-19-2006 at 10:33 PM]
Well, I got it working. At least for now, it has been running for 12 hours without stopping. I talked to a guy who said something about adjusting the metering device, and somehow changing the superheat. Didn't understand completely, but changed it to let more refrigerant flow, and it worked. Also added another 1.5 pounds. So far so good. Compressor temp is 43, has been for 12 hours. I really appreciate your help, and if you have anything else to add, or tips to suggest, I am going to monitor this for the next several days til we leave.