Phantom HP Trips

[icemeister]

Every once in a while I get to a call and the unit is off on manual reset high pressure. I'm talking about basic small commercial stuff like 3-5 HP 3-Phase. I check everthing out and find nothing out of line that might cause a high pressure shutdown.

I usually end up thinking there must have been a brief power loss on one leg to drop out the single phase condenser fan(s) but the compressor had to have continued to run single phase long enough to trip the HP switch before going out on overload protection. Am I right in my theory?

I had one of those calls today and two 3 horse units were down on HP and the manager says there was a power interruption early this morning.

[jacob perkins]

or some problem with just the condenser fan circuit:capacitor,weak motor,lubrication...

[bigbaldito]

I had one once which took me two weeks to figure out.
unit would trip out about every third or fourth day. It always seem to happen in the afternoon.

So on the day i figured it out. I went up there right after lunch and hooked my meters, and gauges and sat there on the hot roof and watched it.

About an hour later my head pressure started to rise and fall. I still didn't get it. Till I noticed the wind was the cause. It was blowing hot exhaust off of another large condensor right into the intake of my unit.

Put a diverter on large unit problem solved. It was a pain but I got er

[R12rules]

I go with Jacob and baldy, but i dont believe you can have a three phase unit remain online once one leg is dropped out .... and have it pump up the system pressures so as to cause the HP control to trip.
If that was the case, you could simply install a phase safety which would lock out the controls and shut down the whole condensing unit whenever the power went sour.


Myself, I would do what Baldi did.

[jappell]

that could well be it, i had one today where i reset the breaker and every thing ran but the comp amps were high, I check voltage...WTF? 3 phase and the pump ran without one phase. I always thought they would lock up. Live and learn.
turned out to be a bad breaker, just so wild it sat there and ran, sure am glad i took the amp probe out!

[R12rules]

Originally posted by jappell
that could well be it, i had one today where i reset the breaker and every thing ran but the comp amps were high, I check voltage...WTF? 3 phase and the pump ran without one phase. I always thought they would lock up. Live and learn.
turned out to be a bad breaker, just so wild it sat there and ran, sure am glad i took the amp probe out!


Your telling us that your unit was "running" and only two legs of the contactor were drawing current?


uh.... maybe with no load on the pistons ... a broken crank maybe... but otherwise she's only gonna huuuummmmm........

[icemeister]

These two units are identical, plain vanilla R22 walk-in cooler systems sitting on a slab out back of a C-Store. I checked both units thoroughly.....no apparent problems that would cause a HP trip. The manager said both were running the night before. All I did was reset the control and now both are running normally.

I've seen this same scenario many times over the years.....the phantom high pressure shutdown. Running on after dropping one leg of the three phase is my only explanation.

I could add phase monitors, but the customer likely won't pay for it now that he knows where the reset button is. ;):D

[brit_in_the _usa]

Ive had liquid or oil slug back cause HP's to trip..hydrolic on the top of the pistons

its maybe something worth looking at if you find everything checks out ok electricly...good luck with your finding.

[thegoodhumorman]

lets see, ground level at a conv store out back-
have seen plenty where either the winos who are living back there place something block air flow, or plastic bags get sucked up into cond then fall away...love the smaell of wino piss GAG!

FYI once on line it will run with only two phases as well.

have seen headmasters stick and trip oil fail and high pressure both ( not at same time or unit) but a marginal charge or malfunctioning valve. Most likely motor dying- gets hot and frops but theres a few from my exp.

[r22coolguy]

A couple of thoughts,

I've seen oil sluggs on top of pistons, they are normally pretty easy to find, after they blew out the discharge line and smoke the room, also called auto-ignition or dieseling. Also I'm interested in the 3phase running when a leg drops out, isn't that called single phasing? and wouldn't that burn out the motor? Hence the term singled-phased? Okay, I got curious and googled the question and here is the link: http://www.usmotors.com/Products/ProFacts/1-124.htm

Interesting enough it can happen and could result in the HP shutdown.

[absrbrtek]

I have seen this happen once before. The condenser got a cross wind and pushed against the fan pressure, they equaled each other out. It was like running the unit with no fan. Funny thing was it was in colder weather in the 50s. I ended up putting a wind break around the unit and the problem went away.
Originally posted by bigbaldito
I had one once which took me two weeks to figure out.
unit would trip out about every third or fourth day. It always seem to happen in the afternoon.

So on the day i figured it out. I went up there right after lunch and hooked my meters, and gauges and sat there on the hot roof and watched it.

About an hour later my head pressure started to rise and fall. I still didn't get it. Till I noticed the wind was the cause. It was blowing hot exhaust off of another large condensor right into the intake of my unit.

Put a diverter on large unit problem solved. It was a pain but I got er

[icemeister]

Thanks for the thoughts. I've considered some of these other possibilities on other similar HP trips, but since this one was on two identical units at the same time I'm betting on the power interruption theory.

Here's (http://www.wisconsinpublicservice.com/business/phase.asp) another explanation of 3-phase motors running on while single phased. It is true that a three phase motor won't start on single phase, but it will run on at reduced power output if one leg drops out.

This store has a 208/120 3 phase service. I wonder if the same deal would happen with a 240/120 and the high or wild leg drops out? (or maybe it makes no difference).

I'd like to try switching off one leg on an old POS unit someday and watch what happens just to say I've seen it.

[icemeister]

The subject compressors are CRJ-0300-TF5 hermetics. I dug out some old Copeland data and found that the MCC (Maximum Continuous Current) rating for these pumps is 20.0 amps. Now considering that this is still slightly below the trip point of the internal line break overload protection and that for normal R22 operation on a walk-in cooler at +25/110 where the amp draw is about 8.5 amps, I can see where remaining two windings could easily continue running single phase and greatly overloaded for a short time without tripping the internals.

[onesidedcoin]

If the system has a head pressure regulating valve take a look at it.I had a system the went through the same problem and finally was able to spot it.The valve was just holding back when it didn't need to but would only fault out about once a week.

[icemeister]

Originally posted by onesidedcoin
If the system has a head pressure regulating valve take a look at it.I had a system the went through the same problem and finally was able to spot it.The valve was just holding back when it didn't need to but would only fault out about once a week.

Yes, there are headmasters on these two units and that's always a possible source for high head problems, even intermittent ones, but as I stated earlier they both went down at the same time (as far as I know).......that's the key. The same thing must have happened to both machines at the same time.

There were no apparent system related problems found that may have caused a high pressure shutdown, so the single phasing run-on theory is the only scenario I can hang my hat on until someone thinks of another logical answer.

[-frozen-ocean-]

have any one of you heard of a hot bas binding line. this line comes from the top of the receiver and enters the discarge side of the condenser.inbetween that line is a differential valve. don't really know the true science of it but it does prevent those mysterious high pressure trips. if any one ever installed one of these please explain.

[thegoodhumorman]

Originally posted by -frozen-ocean-
have any one of you heard of a hot bas binding line. this line comes from the top of the receiver and enters the discarge side of the condenser.inbetween that line is a differential valve. don't really know the true science of it but it does prevent those mysterious high pressure trips. if any one ever installed one of these please explain.

on a Hill rack there may be two valves -one to pressurize the receiver with discharge gas in response to vapor in the liquid line attron sensor, and the other valve (if present) to equalize following hot gas defrost- shoot its been awhile since I have been in front of a Hill rack w attron.

Otherwise it sounds like you are describing a diff valve whch is used in conjunction with a "hold back" valve on single systems. These two combined are now combined into the headmaster valve. It does not vent from receiver but into it as needed. yes?

[Dowadudda]

So a power outage happened. The product was cold and kept temp for awhile. They notice the box is down always like 3 hours after or so. The trip did just like you said. I have sat and watched that happen.

Get your invoice signed and send them the bill, your done. Or sell em phase momitors. But with manual reset so you can still come out and get paid. :D

[k-fridge]

My vote is a condenser fan motor with a "dead spot" where it occasionally won't start. Sometimes extra cold weather will be when this happens too.

I've seen a sticking headmaster or a sluggish fan cycle cause this too.

[icemeister]

Originally posted by Dowadudda
So a power outage happened. The product was cold and kept temp for awhile. They notice the box is down always like 3 hours after or so. The trip did just like you said. I have sat and watched that happen.

Get your invoice signed and send them the bill, your done. Or sell em phase monitors. But with manual reset so you can still come out and get paid. :D

You're the first to say he's actually seen this happen....that make me feel a lot better.

It's just one of those calls that you go out, hit a reset or reset a breaker and you never really find a anything wrong. I hate leaving without a reason for it's going down in the first place.

BTW, new customer with two local stores......referral from another long time good customer with three stores.....but I got cash nonetheless. ;):D

[rickl]

Three phase compressors will not run on single phase conditions. The compressor's overload is resetting before the condenser fan motor's overload allowing the compressor to come on before the fan motor. Install a phase monitor to shut down the system on single phase conditions if it's a line voltage problem. Or install a autoreset high pressure safty. Could be the fan motor itself. Bad bearings, they can run until the thermal overload trips. Could be the compressor contactor allowing single phase comditions also.

[icemeister]

Originally posted by rickl
Three phase compressors will not run on single phase conditions.

The two links posted earlier contradict what you're saying. Three phase motors will in fact continue to run (at reduced power output and higher amp draw) if one leg drops out. Granted, they will not start single phased. Also at least one poster here has witnessed it happen.


Could be the fan motor itself. Bad bearings, they can run until the thermal overload trips. Could be the compressor contactor allowing single phase conditions also.

Again I will say that this involved two identical units that went down at the same time (and BTW both have dual condenser fan motors). It's extremely unlikely that both units had fan motor or contactor problems simultaneously.

[rickl]

The motor may run under no load conditions sure, but not under a load. Try it and see for youself. If the overload does not trip its going to burn a winding.

[mardoman]

C-Store with c-units on ground............. probably by the back door?

Could the phantom be from a vendor or employee breaking down box's or setting the trash bags out back in front of the condenser coils and the wall so the crap won't blow away or block the back door? Just a thought.

Sounds like ya need CSI........... Cooling System Investigator

Good Luck on catching the guilty party, look for the evidence.