View Full Version : RTAA300
03-22-2005, 08:19 PM
See if this scenario make sense to you. Walked up on this particular unit and see that the relief on one compressor has blown. All charge gone. Pumped up system with nitrogen and began leak checking. Found cap tube on high pressure switch (on same comp as blown relief) had been rubbing against lines for dp switch causing my leak. Now, would I be correct in saying that once the unit began to leak, it would try to compensate for lack of pressure and maintain LWT by cycling off fans? Also, since my high pressure switch had a slight hole and designed to cut out at 405psi, it would be possible for it not to catch it before relief blew at 450psi? This ever happened to anyone else out there? Just curious...
03-22-2005, 11:33 PM
I would have to check the IOM to be sure but I think the only reason it would try to cycle the fans would be to maintain the appropiate differential between suction & discharge. First thing I would do is hook the hp to a nitrogen bottle & see when it opens. Then I would check cfm fuses & make sure fans are operational. Maybe a high head condition existed & the pressure was not able to build in the hp because of the leak in the feeder tube. I suppose the rv could have simply failed & opened pre-maturely, but I kinda doubt it. Now you have to be Columbo & get to the bottom of it. Consider all possible combinations. Good luck!
03-22-2005, 11:44 PM
I had something similar happen to me a while back on a machine that blew its charge on a highside fitting and one relief vlv really hissing bad. Turned out that a control glitch occured causing warm water to constantly recycle through the chiller barrel. It appears that the chicken and the egg appeared simultaneously. Maybe something like tis happened with your machine. The way I theorized it was that we had a weak fitting from jump street, high pressure aggravated this and relief started popping off as well. Hope you find it soon. Later.
03-23-2005, 08:38 PM
could be dirty condenser,blown condenser fan fuses-bad fan motors,or slide valve not all the way unloaded while starting .Fix the pressure switch leak ,change out the relief since it has blown it may be weak,evacuate and charge the circuit,when the compressor starts RLA % in p2 menu #27 should read 40% or less .
03-24-2005, 12:17 PM
I would be more apt to believe the relief valve was bad, those machines are notorious for leaking relief valves. The harmonics that the screws deliver really takes a toll on those machines, thats why the oil dp switch had to be modified several years back with a stiffer spring, I would bet you probably had a bad relief valve.
Cond fan logic is terrible on those machines as well, but I have never seen one actually blow the relief, they usually trip off on high head or low oil flow because the head is to high.
03-24-2005, 06:10 PM
I think cold -n- mode hit it on the head. You may have a slide valve sticking in the compressor and it is starting loaded. the high pressure swith cannot react fast enough to stop the compressor in time. This happens a lot usually when the compressor has more than about 25,000 hours on it. Check % RLA when it starts.
03-24-2005, 07:49 PM
cool n mode has it right the only other thing is if the unit is before late 98 it might need a fan staging upgrade kit. before that it never took oa temp into consideration it will start with no fans than try to play catch-up. if have any of thoose other problems. you'll trip head press, low oil flow, or even blow the relief
03-24-2005, 09:34 PM
take the relief valve off and make up a adapter and hook it up to nitrogen and see where it blows at. then test the high pressure switch the same way. if they both test good then the previous post has some good things to check. I myself found a number of these compressors not starting unloaded. two compressors i had last month would start up at 90-100%. i ended up rerouting the oil drain from the piston. that was after i tested the controls and the lip seal.
03-25-2005, 02:27 PM
Check your condenser temp sensor and connections,etc. I thought liquid temp is used to determine fan sequence. Had more than one unit(RTUA), with circuit 1 wired in to cct2, you won't see at full load, but run one circuit at a time, and observe both liquid temps, running and idle. Also, finding leaks on condenser braze joints, resulting in oil everywhere, tiniest pinholes.
03-25-2005, 04:28 PM
I realize you mentioned quite a bit of detail in your scenario, but as always some one will have questions. In the mid 90's there was a TSB about those relief valves on 3 compressor units. It involved the placement of the relief valve in the discharge piping and involved changing the discharge flange to one that was drilled for the relief valve to be installed there. Harmonic vibration would cause the mass of the relief valve to "sway" back and forth untill it eventually broke through the discharge line and blew the charge and most of the oil. Also be aware that these units were grossly over charged at the factory in Pueblo, CO either with refrigerant or oil or in some cases both. Check your service bullitin file for RTAA-SB-12, or somewhere in that area.
03-26-2005, 10:57 AM
I had one of the reliefs blow on the discharge line when I restarted it, turned out the condensor was dirty , it didn't have the eeprom upgrade and the fans would not turn on before it blew the relief.These condensors may look clean but can be severely blocked, probably what happened.
03-27-2005, 08:23 PM
trane service bulletin 11
03-28-2005, 06:08 AM
Joeywitpitman, Iknew someone out there had the brains to to do that. I'm not sure if that's his problem but there's a lot of talent on this site and no one will ask questions, Thanks for your input,signed ga1279
03-28-2005, 08:12 AM
I had a similar situation happen to me as well.
Compressor 1 and compressor 2 of three compressor unit.
Compressor was starting loaded, but also, the compressor made a hell of a racket at s/u, like it tried to pump liquid. The disch. pressure went up so fast (hydrostatic condition?) that the HP sw. couldn't respond fast enough.
What a mess to try to clean up off a rubber roof!
We replaced both EEV's and the evap sensors. No more problems.
P.S. Relief's and HP sw's checked OK.
Just a few more thoughts for you to ponder.
I'd like to hear what you actually find. Keep us posted.
03-28-2005, 07:59 PM
it doesn't sound like he had a problem with the relief valve breakage. it blew. would highly recommend checking the loading and unloading of the the comp. may sure the cond is clean. and if it doesn't have oa sensor and cond fan staging chips it should be done [ex.before 98 it could be 100 degrees outside and start with no fans]. the sensor and chips are under 300 bucks.
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