Danfoss compressor running backwards

[kengineering]

I am replacing the compressor in a Euopean display case. It originaly had a 230-240 V , 50Hz. 404A condensing unit with a cap start induction run fractional hermetic. It is relatively new and the compressor was already removed when I started work on it. The owner was told by the previous serviceman who never returned, it burned out because of the difference in cycles here in the US causing it to run faster. I installed the new compressor, which in the 60Hz conversion model, only comes in a cap start cap run set up. It has a potential relay instead of the cmr relay that was on the original. Problem..Compressor starts and runs but dosn't pump anything. The gauges show nothing. In fact if anything the suction pressure rises slightly then it goes off on overload. After much checking and rechecking i figure there is a mechanical problem so I recovered the charge and pulled off the suction discharge lines. Just for kicks I turn on the compressor and it is running in reverse? The suction line is blowing and the discharge sucking.
I'm really losing hair over this one. Ken

[Dan]

Sounds like some sort of rotational compressor such as a scroll or rotary instead of a reciprocating compressor with pistons. What's the compressor model? Not sure I understand why a single phase compressor would have reversibility, though.

You come up with interesting stuff, Ken.

[Rob S]

Had a simular problem once. Had to install a superbooster on a PSC compressor to get it up and running for the time being. After I did the Condensor fan started to run backwords. Disconnected the compressor and removed the start-assit. Condensor fan began to run the normal direction again. I put my hand on my head and said.... Why Me?
Only explanation which made since.. start-assit was causing the volt/amp lead/lag to do something very weird. Just wish I had a scope capable of checking the cycles at the time.
Corrected with some higher voltage/mfd run caps. May have just been the Pot Relay not opening properly. Didn't have another start-assit to try at the time. Was a weekend call.

[afeef]

dear ken
if the compressor is semi-hermatic as you said,
the only reason i am thinking about is:
some one had instauled the valve plate 180 degree of its original direction,,,,in this case the suction valve will face the discharge line , and the discharge valve will face the suction line
so the refrigerant will pushed over the suction line
this is the only explanation i can give to your case
open the valve plate and check the direction of suction +discharge valves
replay me please
regards
faithfully
afeef

[kengineering]

The compressor is not semi hermetic it is a fully Hermetic Danfoss sc15clx recip compressor. It is rated for 230-240 volts. I have measured the voltage on site to be 210 volts. I have removed the supplied start kit and connected a run cap. I have left the relay out and used a jumper to the start winding to get it going and it still started with reverse rotation.
Ken

[BESC5240]

Maybe a silly question Ken, but is there no mix up between de discharge and the prosess tube (they have the same connection size: both 1/4").
On this compressor the discharge is just beneeth the suction (next to the junction box). The process tube is to the other side.
Bruno

[Peter_1]

The compressor is not semi hermetic it is a fully Hermetic Danfoss sc15clx recip compressor. It is rated for 230-240 volts. I have measured the voltage on site to be 210 volts. I have removed the supplied start kit and connected a run cap. I have left the relay out and used a jumper to the start winding to get it going and it still started with reverse rotation.
Ken

How do you know it's running backwards?
Even if it runs backwards, discharge remains discharge and suction remains suction.
Afeef, you can't open a Danfoss compressor. Think BESC5240 gave the correct answer.
What have you done with the process tube?
It goes in overload because you are pushing everyting in the closed discharge tube.
Measure once current.

[davej]

been watching this thread and agree with Peter it is not like a scroll pot. it will only discharge out of the same ports. respectfully suggest you check you have used the correct ports, i have attached a link to the info on the pot which may assist.

http://rc.danfoss.com/TechnicalInfo/...2_Cf54r302.pdf

[kengineering]

Davej,
I have the same pdf from Danfoss. Great information but it wasn't much help with this problem. The 60 cycle replacement for the US was a physical clone of the original. All tubes and the fusite conection are identical. This has been checked.

How do you know it's running backwards?

That is to say, before I tore out my last hair, I removed the compressor from the the suction and discharge lines but left it in the electrical circut. I started the compressor open to atmospere and the suction line ( the larger dia.of the two copper connections and located above the smaller dia. discharge line.)was blowing. I expected to feel it suck. The discharge line was sucking but it was weak.

I have been on the phone with Danfoss and thier Engineers are scratching heads trying to figure this out. It'll be reterned to them but I'd sure like to cut it open myself. Anyone know if you could use a plasma cutter on one?

Keep the cards and letters comming boys and girls
Thanks , Ken

[Peter_1]

Ken, I opened several small compressors.
You don't need a plasma cutter, you just need a grinder and grind the welding where they have joined the 2 parts together.
It will open like nothing.
If it's true what you're saying, then you have a collector item.
Sell it on Ebay.
Like last week here in Belgium: they filled in teh Coca Cola factory some Fanta botlles with colc and vice versa.
These has become collector items.

[Double V]

Hi Ken

I started the compressor open to atmospere and the suction line ( the larger dia.of the two copper connections and located above the smaller dia. discharge line.)was blowing. I expected to feel it suck. The discharge line was sucking but it was weak. 

Was the discharge & suction weak. If this is the case, I have seen compressors with similar symptoms, when opened i have found a small part of the gasket blown. Therefore it discharges into the housing of the compressor & feels like outlet presuure on the suction pipe. It is very weak though & you should be able to block both the discharge & suction pies with the compressor still running.

[Peter_1]

Ken, what was finally the solution for your problem? We're eager to learn something.

[old gas bottle]

cant see it running backwards or connected up wrong that would be insulting,i got caught out once where the rubber sealing bung had been broken off down the suction port in the comp on a new cabinet,poke a brazing rod down there and see if its blocked,may even be full of braze,[not being funny]worth a try,or dump it and fit another one.

[wambat]

Normally a small single phase reciprocating compressor doesn't care which way it's rotating it will pump either way, however, if the valves are defective then it may not pump at all

[nazimzamur]

Change the compressor with a new one and give back it to dealer.

[Ireland]

I agree with the last couple of posts.

It must be installed wrong or the pot is knackered.

Either way it will have to come out.

Stick in another pot, possibly a different make to be double-sure, and I reckon you'll hear no more from it.

[Ireland]

Actually I just saw the date of the first post.

What was actually wrong????????

[NoNickName]

There are two ways to start a single phase induction motor: split phase or capacitor.
Split phase is normally used when high starting torque is required, which is the case of a compressor.
If the start winding of the split phase is wired with reverse polarity, the motor will start the other way around.

[Ireland]

It still won't matter with a pot.

The piston will go "down and up" instead of "up and down".......... lol

The pot must be faulty or fitted with the pipes on backwards.

[NoNickName]

It still won't matter with a pot.

Of course, this is clear. It was just to emphasize that a single phase motor CAN actually turn the other way around