Intermittent High Pressure Trips

[icemeister]

Here's one I ran into last week that I thought would be of interest.

New Meat Market, Old Customer who had the job installed by an outfit out of Miami. He called me a while back to see if I would cover his service work.

Sure.

I have an intermittent HP trip on a new Russell 6 hp Discus R404A air-cooled outdoor unit on the roof. It's tied to 35 ft of new Tyler (RIP:() double-wide island FF cases. Theses were just started up last November.

Well, come the first hot weather over 90ºF I got a call the system was down, find the HP switch tripped, reset and all looked OK.

It happened a couple of times after that so I get back there to investigate a bit.

Now all was operating normally. Pressures at about 16/260 with -10ºF DA and 90ºF ambient.

I ran through a manual defrost, restarted and saw the suction pull rapidly down to about 30# but within a minute the discharge shot up to 380#. Hmmm?

The head shouldn't be going up that high just because the suction rose from 16# to 30#. I'm thinking overcharged? No couldn't be. I know this unit's 30 lb. vertical receiver isn't big enough to handle a full system pumpdown, but it should handle normal defrost cycles, low ambients and such.

Anyway, I try a manual pumpdown and within 30 seconds I'm down on high pressure...tripping at just under 400#.

OK.......

So I recover 15 lbs of the Orange Juice and start up. Now the SG is flashing like a SOB. :eek: I try a defrost again....just for the heck of it....and the post-defrost head is now only 280-285#.

Broken dip tube maybe? That's my bet.

[cold spell]

I would heat the reciever to verify it is full. If full then broken diptube or installed backwards.

[Dowadudda]

Torch the receiver. We had a call like that, it went on for a year. I figured it out. Sounds almost identical symptoms.

[jpsmith1cm]

Maybe and maybe not related, but a national chain recently had a string of problems with the weld around the dip tube leaking inside. Draws a mix of vapor and liquid.

Regardless, I agree. Dip tube trouble.

[powerup]

Great problem all should be aware of. Not sure I would have ever thought of a broken dip tube right off. Look forward to seeing what the resolution is.

[icemeister]

I was about to torch the receiver but I got chased off the roof by an fast-approaching thunderstorm.

I left it with the SG flashing just a little by putting 10 lbs back in, but they were still out of danger for any more HP trips.

It's not piped backwards....I've had one of those before.

[jdwendling]

Had a new Russell unit do that a few years ago when the warm weather began . Started it up in the late winter. The discharge service valve was not opened all the way up. Who would've thought. Never used that port. Always used the receiver liquid line service valve. Now I check them all.:rolleyes:

[Dowadudda]

when I found mine, I had the fortunate pleasure of knowing a bit of the history of what the previous techs did. So by knowing some of their troubles with the unit prior to going there, and then when I got there and screwed around with it for a few minutes, the light bulb went off. Chased down to the van to grab the torch and I was pretty tickled to have figured it out. It as the first time I had ever run into it. After 13 years.

Old timers like my dad and others always torched the receivers. Always. I worked with a guy who would go on a call, grab his tool pouch and a small hand held mapp gas torch, right off the bat.

So I have since then always torched my receivers on charging units ect. There have been a few rack receiver liquid level indicators I have caught that were way off due to my doing it the old fashioned way. And then ask yourself, How many guys would rely on that indicator and be completely wrong?

[Joe Harper]

How do you tell if the receiver is piped backwards??

[crackertech]

http://sporlan.jandrewschoen.com/5-158.htm

[sumdumguy]

now this is why I come to this site. 2fingcool!!!
nice education. I want more brain teasers
:D

[icemeister]

How do you tell if the receiver is piped backwards??

Whether it's piped backwards or if it's got a broken dip tube, the symptoms will be similar...ie, you'll see an unusually small change in charge between undercharged (as in a flashing sightglass) and an overcharge (as in a HP trip).

To determine which problem exists, often it only involves looking at the receiver's connection configuration....(See attachment).

Vertical receivers are easier to figure out since the inlet is almost always above the outlet. If it's got only one service valve, that's the outlet, or King Valve.

Horizontal receivers are more problematic. If it has one connection at the bottom of the shell and the other on the side or the top, the bottom one is always the outlet. Many times they're both on the side or on top, so you can't really tell by looking at it.

Some techs will say just look for the markings on the shell for "inlet" and "outlet", but don't assume those are correct either. That's what I found on the horizontal receiver that was "piped backwards". Actually, it was piped correctly per the marks on the shell, it was just marked wrong.

That one was easy to verify after recovering the charge, removing the Rotaloks and physically inspecting the connections with a light and probe.

[wannafreeze]

Ice,do you see any reason that a dip tube connection can go bad due to circuimstances,such as high pressure/temperature exposure? Or is it the factory defect everytime?

[wannafreeze]

when I found mine, I had the fortunate pleasure of knowing a bit of the history of what the previous techs did. So by knowing some of their troubles with the unit prior to going there, and then when I got there and screwed around with it for a few minutes, the light bulb went off. Chased down to the van to grab the torch and I was pretty tickled to have figured it out. It as the first time I had ever run into it. After 13 years.

Old timers like my dad and others always torched the receivers. Always. I worked with a guy who would go on a call, grab his tool pouch and a small hand held mapp gas torch, right off the bat.

So I have since then always torched my receivers on charging units ect. There have been a few rack receiver liquid level indicators I have caught that were way off due to my doing it the old fashioned way. And then ask yourself, How many guys would rely on that indicator and be completely wrong?

http://hvac-talk.com/vbb/showthread.php?t=274482

#2 thread gives a different view of torching.
You think it's okey to use turbo torch instead of mapp gas torch?
I don't wanna keep one more thing in the truck..
Also you torch the receiver while unit is running right?

[jpsmith1cm]

I have used many different torches to 'torch' a receiver.

A simple propane torch, a MAPP torch and an ox-acet rig. All provide good results. Just a matter of what was in my bag or what I grabbed first. You aren't trying to burn a hole in it, you are just heating it up a bit.

I suppose you could do it with a heat gun, it would just take longer.

[icemeister]

Ice,do you see any reason that a dip tube connection can go bad due to circuimstances,such as high pressure/temperature exposure? Or is it the factory defect everytime?

It appears most of the bad dip tubes are manufacturing related. As for them failing later on down the road, I suppose anything is possible.

[cousteau]

I have had some bad experience with Russell condensing units and high head problems.

Lots of undersized condenser motors. They never trip the internal when you are there.:mad:

I had one condenser circuited wrong on the return bend side . Ended up we were only getting pass through about 1/3 of the condenser.(That was a B**ch to find) I had been off the tools a few years already at that point and was helping out with a start up. Thought I had lost my touch for a while.:o