Help with another "Goodwill" call...

[Jake]

I went out tonight to look at a small Rheem split system. I think it was

2 ton manufactured in 1991. Copeland Hermi.

The compressor wasn't running, OFM was.

Single phase 240 V.

I kill the power and check the compressor. Good resistance from each terminal to one another. About 1 ohm between the two hots and 4 ohms from one to the start winding. No shorts to ground.

This setup has a dual cap for the fan and comp. There also appears to be a factory hard-start built in. The hard-start relay showed closed (as it should) with the system powered down.

Put power back to the thing and I don't hear a darn thing but it won't run. I never even heard it try to start. 240 V to both run terminals and

240 V between one run and the start. The other run to start showed about 15.

I don't know if the internal O/L's are working that fast or what's up. I suspect a start or run cap... but I thought I'd get some more opins.

I didn't have the time rip the cap out of the cabinet... Rheem made it a pain (Payne for Johnny) on this unit. I'll check it next tomorrow or so...

Why the heck would a internal trip that fast? I can't even see a current draw when it should be trying to start.

Any suggestions?

Jake

[gofish]

and the compressor wasnt too damned hot to touch?? Now there's a first..............

turn power off for 24 hours. connect a TO-5 hardstart kit to Start & Run terminals and turn on the power & mash in the contactor. If it starts up, pull the oem potential relay and run cap and install new oem parts. If it doesnt start up, warm up your compressor changing tools.

[Fat Eddy]

Still missing a reading here, ( and these sound low ) in general the two lowest will add up to the highest, ( approx )

Nothing here says that it is not trying to start, you can not tell by listening, that is no way to verify current draw.

They probably do not work that fast, but could.

If the start winding is damaged the I/O can trip pretty quickly,

Jake,

We need to go back to fundamentals here, get all three winding resistances, verify that the cap is ok, Try to start the unit with an amp clamp on the circuit and set it to save the max reading, then if it does not start, shut the power down and read the winding resistances again ( quickly), if they are now open then you know that it did pop the I/O.And if your start components are working properly then you have a bad compressor because of a defective overload or a locked rotor, but you need to know what it is doing as it tries to start, thats the key here I think.

Fat Eddy

[Stormin Mormon]

As Fish says, the hard start kit is worth trying. I'd also want to check the cap for short / open.

Most of the time when I encounter a bad compressor, at least you can hear it TRY to start. Or, it trips the breaker right off. That's a really odd combination of events.

Might want to check the voltage at the compressor while it's doing all this. You could have a dirty connection, and the voltage is dropping way down during the "trying to start" times.

Please let us know what you find.

[HeatMan]

Noon-Aire needs to jump in here.

I don't recall ever seeing a factory hard start kit on a 2 ton Rheem unit, especially from 1991. Something doesn't jive here. I'd rip it out and install a SPP6 or equalivent.

[Noon-Air]

[Noon-Air]

Umm.... ok

I have one like that to replace in a 4 ton Goodman today

Need model and serial number to see if it was a factory installed accessory

If its immediately throwing the breaker, the SPP6 isn't going to help.

It sounds to me like internally shorted windings.

Shorted/grounded windings

[Jake]

I'll try and get that tomorrow... if I can make it back over there.

There is NO breaker or fuse trip. The compressor doesn't draw any current even though I can measure resistance across ALL the windings initially. The compressor wasn't too terribly hot.

The measurements I gave initially sounded about right for that size compressor. If I had internal short.... I should get an external OCP trip, shouldn't I?

Steve, I already measured (and even megged) the windings. I don't find a short anywhere. The compressor has V at the terminals but doesn't draw any current. I'm going for Paul's thought that the connects are dirty or loose. A condenser sitting outside for that long could stand to have that crap cleaned up, anyhow.

My real question, I guess... was how fast a internal O/L trip would occur... and thus indicate a mechanical problem in the compressor.. or a failure to start due to bad caps?

Jake

[Barry]

How bout an open internal overload.

Barry

[~^Johnny^~]

If it shows continuity with a DVM or VOM, but goes to high impedance with mains applied, that tells me something...

rectification, most likely.

Try the ohmmeter on each pair of terminals with meter leads switched.

Corroded, overheated, or otherwise buggered connections cause weird symptoms.

Pull the wires OFF the compressor terminals and take continuity, with a good DVM in "diode test mode", swapping test leads on each reading.

Bad connections which develop "parasitic rectifier junctions" can ohm out fine, but go "open" when hit with higher current. As far as the compressor is concerned, you got to isolate the problem between =internal= and =external=. If nothing gets warm to the touch on the outside, and current draw is at or near zilch with power (full voltage) applied to the compressor, it's probably (99% positively) internal. ;`(

Compressors do not always get hot when they go bad.

[~^Johnny^~]

Put a scope on it, with a current pickup coil.. set it to TV VERT internal sync, auto trigger, and about 20 ms/div sweep time. Do this on each lead.

Apply power. It'll show you exactly what's going on.

[Stormin Mormon]

There is NO breaker or fuse trip. The compressor doesn't draw any current even though I can measure resistance across ALL the windings initially. The compressor wasn't too terribly hot. CY: As you are an electrician with excellent safety awareness, I can suggest to check at the terminal box on the side of the compressor. Be sure there is 220 VAC available during the compressor's attempts to run. More than about 10% drop will fail to start a compressor. Since it's warm at all suggests either trying to start, or the crankcase heater is active. Might want to also check for voltage drop across the contactor. See if the contactor is warm. Maybe a pitted contact point.

The measurements I gave initially sounded about right for that size compressor. If I had internal short.... I should get an external OCP trip, shouldn't I? CY: You'd think if there was a short to ground, the overload or the breaker would trip.

Steve, I already measured (and even megged) the windings. I don't find a short anywhere. The compressor has V at the terminals but doesn't draw any current. CY: Well, since you've checked for voltage.... Since you have good voltage but no current draw, the only conclusion is that the run resistance is high. I know, "no xxx, sherlock!".

I'm going for Paul's thought that the connects are dirty or loose. A condenser sitting outside for that long could stand to have that crap cleaned up, anyhow. CY: I really wonder, did you keep the V meter on while it was trying to start?

My real question, I guess... was how fast a internal O/L trip would occur... and thus indicate a mechanical problem in the compressor.. or a failure to start due to bad caps? CY: I don't know about the big compressors, but the ones I've worked on power up for about half a second, and then trip. They reset after about 60 seconds. So, you'd have to watch the ammeter and listen for one or two minutes, to hear it trying to cycle. Cleaning terminals is good. Also check for voltage drop across the single or double pole contactor. Beyond that, the compressor may not be savable.

Jake

[zero]

Jake , Even though It's been almost 20 years since I picked up my gauges for my pay, one of my most eye opening, underwear changing memories have been blown overload disks. Multicolor flames/oil and smoke, VERY loud boom. Very transformer like. 8-O After the first one (that's all it takes) I never approached a energized tin-can peckerhead the same way. (And the cover and clip DO serve there purpose.)

As I read this thread, you're definitely been playing musical chairs with this event. The last memory for me was a 10 ton 3-phase on a rooftop. (In hind site, nobody would have been there to stomp me out.) A green 3-4 foot fireball that fizzled to softball size after a good 5-7 seconds.

3 seconds before I was checking voltage at the terminals.

Corrosion can be a problem on these terminals. A visual is very deceiving. Until you pull the terminals and wire brush , then the corrosion is noticeable. A zinc-like corrosion/breakdown? Metallurgists please speak up now.

You would think they should be making them gold plated now, like my stereo cables. :o)

Good luck , Jake.

-zero

[gofish]

finish your story. were the terminals in your situation corroded? did you arrive at a conclusion as to why the peckerhead blew?

i myself have seen some mighty corroded comp spade terminals, corroded to the point that only a split bolt would work in securing a wire lead to it....though never seen one blow out just because it was corroded......

[Jake]

Neither have I... so I'd like to hear more.

I have seen them slowly melt more than once due to heat from bad connections, though... particularly on 3 phase.

Jake

[Noon-Air]

Replaced a compressor yesterday.... Bristol recip... meter said it was ok... good readings, but tripped the breaker immediately when it was energized. when I went to put the gages on it to recover the refrigerant, it was dead empty. turns out that it blew a terminal out of the peckerhead. There were no outward signs, no oil, no burnt wires... just dead compressor.

[zero]

I thought I did? No problemo.

Do not know if they were to start with, not able to determine afterwards.

I feel more exact saying when the discs failed ( the 3 I remember) either one or more terminals were hot enough to light-off the oil/refrigerant mix. (makeshift oil burner= atomized over 70 psig, spray pattern changing as the hole gets bigger, but ready to burn) or as the disc failed, the now flying energized wire/terminal arced across ground for ignition.

And of course you both are correct. I didn't mean to imply that corrosion>disc failure.

The footnote here is the pressure and fuel potential behind the tin can.

I believe the corrosion and its results are no different than any other terminal, lug or relay. In saying that, a relay or contact that has many cycles and suffered contact point degradation along WITH a bad terminal connection next to it, getting way too hot can cause the pressured disc to fail. One of these units that I remember better, was frequently tripping on internal overload. So suppose here you have a open peckerhead with a corrosion build up to cause voltage drop upon start up, causing the Klixon to trip 19 out of 20 times. Should the Klixon fail closed, you've got a hot plate wire glowing hard until the wire melts or the circuit trips or the terminal insulator fails.

Yes that was the case with myself on the first few I happen across. Noticing a large oil spray pattern from under the j-box cover? No problem. Replace compressor, another job done, the end. Man?I REALY wish someone would have told me about the fire ball potential though. Messed my mind up for a while. ( More than the average mind messedupness I wallow through) :-)

Q: Has there been a white paper or analysis that addresses this failure that anyone is aware of?

-zero

[gofish]

ok, I'll bite. How could your meter say it was ok (ohming the windings?) if one of the terminals had blown out?

[Jake]

You beat me to it, Fish...

I'm curious how that would happen too...

Let me state this whole scenario one more time.

Rheem early 90's 2 tone split. No cooling. OFM running. 230 V single phase with dual service cap (fan and Compressor). Factory hard-start (it's right on the skinny). Compressor not running. 230 v present between common and run terminals at the compressor terminal block. ~ 15 v present between common and S terminals at same. While disconnected at the contactor the compressor measures expected resistance between C and start/run. Properly rated external OCP doesn't trip. Compressor very warm to the touch... but I could keep my hand on it.

I threw the disco off and hope to get more informative info after it cools down.

I haven't gotten back out there... been busy as heck helping customers. I'll certainly do so either Friday or Saturday... the residence is an older couple and it's supposed to get really hot here in Indiana next week.

Jake

[aka-SBM]

Correct. Got one Im heading out to as soon as the supply house calls...and changing one out under warranty...its locked tight as hell, but one would never know it. Internal trips in under half a second, everything checks out fine, min draw when started, cool case.