Crazy odd compressor problem 100f superheat

[idontgetit]

Master bilt mclz120 with 12 horsepower bitzer compressor. A little bit of history Prior to 6 months ago unit would occasionionly shut down without evidence of why. It would be around 2 months and between high alarms on the controler and the unit having shut down. However, on restart unit operated near perfect. Now about 7 months ago was actually able to catch problem at time reversing valve was stuck i was able to tap on reversing valve and get it to shift cooling. Upon restart note that head pressure extremely low pump town test Bad valves. Replaced the reversing valve, a brand new compressor not reman, drilled all the traps, and hold vacuum down somewhere in the 3 hundreds.


Fast forward to Last month about mid December unit Shuts down again.Customer restart shutdown again.I can tell from the graph data shutdown was after a defrost. Fire the unit backup interstage superheat running my 37 to 39ﾟ Notice frost starting to form on the liquid line Coming out of the interstage cooler.enough odd going on I to go ahead and gage up.


Running about 95 to 104 head pressure Anti 6" of Mercury on 404a. Check the interstage again superheat running 37 to 39ﾟ Superheat and return vapour from evaporator 95 to 105 Which sounds high but with a -60 evaporating temp and a 70ﾟ Box it wasn't a surprise in the middle of hot pull down. After talking to master bilt, a quick pump down test indicates bad valves again! But wait there is more.


Order valve plates pulled the heads of Valve plates show no damage. Took the plates over to the local rebuilder he inspected saw one spot that might have been leaking through head gasket on 2nd stage. Wasn't real evident from a visual inspection of course valves could be leaking but not chipped damaged bent or lifted no blistering from liquid oil flood back etc.


Install new valve plates fire up unit no head pressure above 100, superheat at 95 to 100, interstage 37 to 39 frosting starting in the liquid line after the interstage cooler. Ran for perhaps 15 minutes waiting for some level of balance, not happening so I did another pump down test, leaking back again!


When I say leaking back I mean going from 28 to 29 inches in 15 seconds after service valve closed to leaking back into positive pressures in under 60 seconds.


Things we know, service valves and compressor is tight to below 450 microns. No visual damage to heads, block, or pistons, almost mirror polish smooth. Initial response is that these compressors do NOT have an internal bypass.


Wide open to thoughts and suggestions, I have a real expensive toy that has me stumped!!!

Ambient outdoor in the mid 20s.

I would include pics but i dont have any hosting site.

[idontgetit]

As quiet as Bitzer in here.

[patpinet]

I'm really interested in the problem your facing. But I don't have the knowledge to help you.

Have you talked to bitzer about it?

[idontgetit]

No solution yet, but got some odd feedback from Bitzer today.

Said without at least 100 psi of differential their valves will chatter and leak back!

Never heard that one before, got a wtf moment out of me fore sure. May no more tomorrow.

[Snapperhead]

I would include pics but i dont have any hosting site.

You dont need a host , do you have a desktop , or laptop ? you just click on "Go Advanced" then "Manage Attachments" , then "Add Files" , then "Choose File" and that will bring you to your pictures folder , or near it , then after you find the picture click "Upload" , then at bottom of page "Done"

You might try putting this post in Commercial too

[steve wright]

Those new valve plates need to be run in for 24 to 48 hours to get a valid pump down test. What type of interstate desuperheating are you using?

[Snapperhead]

Im thinking your problem is somewhere else in the system ....

[dodgedart401]

Hi, OP says you witnessed a stuck reversing valve. Bad RV notoriously can look like a compressor problem.
I am not familiar with the unit your working on but if it has a RV then it should be checked for trouble.
Basic RV troubleshooting is available no doubt on this site on other threads.
Warming small pilot tubes slightly while operating valve to clear these lines has worked a few times for me.
Valve replacement is the usual remedy .

[idontgetit]

Cant get the files to drag and drop with pad. You can see them in my profile album if you want to look at tgem.

Tbe valve plates were not likely tbe problem if the 100 psi dofferential Bitzer says must exist as it wasnt ther at an6 of the test.

I agree snapperhead, going to do a lot more testing tomorrow now that the box hqs acclimated. I shouldent have put so much confidence 8n tech support.

Dodge, the reversing valve was replaced at the same time as the comp 6 months ago, went to a spring loaded design as well that forces cooling mode.

[idontgetit]

ok, got by after acclimenting the box and got a bit more info, though I don't find it definative at all.

Out door temp at 27f it might have been 25 and a little effect from the CFM's
SCT 46f aka 94 to 95 psi on 404a at discharge service valve, 43 aka 90 psi leaving the condensing unit.
Discharge temp approximatly 2 and 1/2 feet from discharge valve (after a u-turn and vibration eliminator), 102f
Liquid line entering the reciever, 43
LL leaving the condensing unit 0f
SST -62f
Superheat about 1 na d 1/2 foot from the compressor service valve, 35f
interstage superheat 36-40f

Hit a defrost, unfortunatly it wasn't expected so only gathered limited info by the time we got to the roof.

inlet sensor 33-36, coil was cleared
97 psi head
Liquid line -5.3
return vapor temp at comp -51
entering reciever 35
leaving reciever -6.5

on return to cooling numbers pretty much mimiced the previous cooling numbers so no additional data there,

2 full days of run time, ranging from -38f at peak of defrost and -42 with a submerged probe in glycol to monitor the room.

[Red Man]

You say it shut down after a defrost. What exactly did it shut down on?

[idontgetit]

I wasn't there i can just tell from the chart reader. The customer is fairly well versed on the controllers and said they just had the ha high room temp alarm, no others.

[Red Man]

How did they reset it?

[idontgetit]

At the controller I suspect, I doubt the hit the breaker. It ran for about 30 mins and alarmed again and they shut it off at the evap which shuts down the controller as well. There were no problems up top, oil monitor fine etc.

[Red Man]

So you think they reset the controller, but the controller only showed a high temp alarm. I’m not familiar with this system, but if I were you I’d try to figure out what could shut down the system, not throw an alarm, and be reset however it was that they reset it.

[idontgetit]

Yeah that is what led to the valve plate replacement because it wouldt build head or hold a vacuum.

It was back mid December but this unit has had a gremlin causing it to shut down for no apparent reason for a couple of years. When I caught the reversing valve stuck I thought it was solved.

I haven't had a good reason to gauge up on these systems in the winter so I found the lack of head pressure control and the freakishly low head pressure.

[Red Man]

I’ve got a customer with a similar system. Their old location had a master built with bitzer compressors. The new location is Krack with bitzer compressors. I’ve found the compressors locked out on motor protector, requiring a power cycle to reset. These run 404A in a vacuum. Typical low pressure switches don’t work well when set to cut out in a vacuum. I’ve seen the low pressure switches intermittently fail to open, causing the compressors to overheat and lock out on the motor protector. Just a thought. The ones I work on are electric defrost. I’ve heard they tried hot gas defrost at some sites and it was a major failure.

Your head pressure is crazy low as well. No head pressure controls?

[idontgetit]

These are hot gas. There is no head pressure control on them at all which baffled me, I thought the cds valve would be doing it but only during defrost according to master bilt. I did have a dead hp transducer that may have lead to the original shut down. After spandex sold off they screwed the numbers on the 500psi transducers which parts town put at 21 days to get. Same voltages as the stainless sporlans so tossed one of them on. I didn't do the cable but I did test the out puts after and it was fine.

I replaced this comp and reversing valve back in June. The unit next to it got smoked by lightning but only the compressor??? Went phase to phase in the electrical box. Replaced that comp in September.

I had a 7.5 discus that cracked a line and sucked a bunch of water into it, replaced it with another of the 12 hp bitzer about 1.5 years ago and the other discus unit is on with it as back up. Set it to -38 so it runs very little.

Haven't experienced any defrost issues other than the crappy drain line heaters, I just reran the externals all the way to the pan.

I would say they are fairly problematic units overall. Ruptured oil lines, blown vibration eliminator, eev's, oil level control, boards, and motors.

I did go with high water capacity 48' driers at the comp change as well. I am pretty annoying to my boss because I won't cheat on the vacuum and it usally takes 36 to 48 hours to get em to hold below 500.

[idontgetit]

Ok, learned they are resetting the unit by cycling the circuit breakers.

I think you may be on to something with the low pressure control since I have seen it at 8" on a slightly warmer day and the cut out is 12 per the scale it is quite possible.

Took the numbers off the sister unit next to it, identical set up with evap 2 floors below etc. And they were basicly the same, 5 psi higher is all on the head pressure.

You can see from the chart where I am saying it failed coming out of defrost or very shortly after. With the glycol it is a bit behind on the temperature changes.

[Red Man]

There’s not many things on most refer units that’ll reset by cycling the main power. Motor protector is one of them.