Scroll Compressor draws about 10 amps more than it should

[timebuilder]

First of all, you need to measure voltage at the terminals, because you can't assume you don't have a bad wire, a bad crimp or a bad connection at the compressor itself. Second are you a homeowner or a technician?

[Saturatedpsi]

Got my doubts, based on the reported suction pressures, but I'm not there so...

[Butch1234]

I am a licensed professional electrical and nuclear engineer with extensive expereince.

[timebuilder]

In that case this thread belongs in the AOP section.

I am the son of an engineer and I have really extensive experience and I can tell you that there is a broad difference between being an engineer and being the guy who fixes things. This is mainly manifested in the difference between the world of theory and the world of reality.

Btw, Butch was my name my parents called me until I went to private school!

[Saturatedpsi]

I am a licensed professional electrical and nuclear engineer with extensive expereince.

You're over-qualified for heat pump diagnostics...

[Saturatedpsi]

In that case this thread belongs in the AOP section.

Please make an exception in this case...I'd really like to see the final analysis/diagnosis.

[Butch1234]

you are correct...but I am also a ham radio operator and an over the road truck driver at one time...I know which end of a soldering iron to pick up.... I designed this system to a large degree...or have had to fix what the original supplier provided ....a real real long story...maybe will post once we get this fixed I will let you guys know if it is the CPR the more we talk about it here the more we are convinced this is the problem but will check tonight...I appreciate the feedback because as you well know...when you have a technical problem that does not make sense you got to bounce ideas off other folks to see if you can sort it out...thanks

[koolkahuna]

Removed post.

[koolkahuna]

Place a service call with a professional hvac/r service company, ask for their best tech, he will come and tell you what you did wrong. You aren't qualified to work on this my friend. Just like I'm not qualified to work on nuclear powered toilets...
I have run into your type before, you have the theory, education and paper on the wall. You just can't do it in the field like those of us that are trained to do this.
I see what you are missing but I ain't tellin'. Did you pull a permit for a pressure vessel system? Are you licensed?

Uh-huh.

Sent from my SGH-I747M using Tapatalk 2

[timebuilder]

Please make an exception in this case...I'd really like to see the final analysis/diagnosis.

Moving a thread would be up to the mods.

I too, am curious about the outcome. I just think we need to ask questions about the poster sooner, so we don't end up with tech stuff being indexed by google.

[Butch1234]

actually I am qualified and I am working side by side with the contractor that put the system in...so if you know something that we are missing you could point it out

[Butch1234]

CPR Valve update
We adjusted the CPR valve to see if it would lower the motor current. Lowering the suction pressure to 40 psi did lower the current but not to the compressor manufacturers value. The motor current was still about 8+ amps above the table for the compressor. At 40 psi the suction line iced up since the line temp was about 20 F so since it did not really lower the motor current (went down about 2 amps only) we tweaked it back to about 65 psi ( 36 F). The CPR was supposed to be factory set at 70 psi but we found it closer to 60 psi in actual use. The CPR valve (I think it is a Sporlan valve) did not respond the way I have seen other pressure regulators behave. The CPR valve is between the accumulator and the compressor suction (loop pipe after CPR valve). The adjustment screw (fine thread) has about .75 inch travel. The response to adjustments is pretty flat (no change) over most of the span….so one could probably leave the setting almost anywhere and get the 60-65 psi suction pressure we were getting. On the surface it appears the valve is working OK but I would have expected a more responsive behavior to the adjustments….also when the compressor was shut down and then restarted the setting seemed to drift higher (at 62 psi before shutdown…at 69 psi when restarted then the suction pressure would drift lower as the compressor ran, i.e. back towards say 64 psi). Perhaps someone on this board has experience adjusting these valves and can comment on what we saw. In any case the rattle in the compressor subsided a little with our tweaking and that was a good thing.

So for now still no idea as to why we are drawing the high current. My suspicion is that the mass flow rate through the compressor is much higher than the table and this is why the current is high…I have seen that with centrifugal pumps…but the suction and discharge pressure would also reflect the higher mass flow rate????? So back to the drawing board????

[OldSchoolMech]

So your an engineer bust out a Enthalpy chart and map out your refrigeration cycle.

So you check the charge yet?

[Butch1234]

yes we lowered the charge a little but it is supposedly where it should be thanks

[Saturatedpsi]

CPR Valve update
We adjusted the CPR valve to see if it would lower the motor current. Lowering the suction pressure to 40 psi did lower the current but not to the compressor manufacturers value.

Which was predictable, IMO...both liquid and suction restrictions generally result in lower
amp draw.

Since the initial compressor ran "normal" (?) and the 6 (?) subsequent replacements failed (all due to high amp draw?), logic dictates something is amiss with the system.

I know of the three issues external to the compressor that will cause high amps:

1) High head pressure/compression ratio, which your reported numbers don't indicate.

2) Liquid flooding which doesn't seem to be the problem, though a superheat measurement should confirm or eliminate the possibility.

3) Some electrical issue, which you say isn't a possibility.

High head pressure is most always due to low condensing or too much refrigerant. Oftentimes a tech will overlook a liquid line restriction and overcharge in an attempt to raise saturated suction temps. They either don't measure head/subcooling or don't know what normal head and subcooling should be. That's why I initially asked if there could be a restriction between the compressor and point of high pressure measurement.

Liquid flooding, without high head pressure, could be the result of an overfeeding metering device, or high head pressure with a fixed metering device, or low evaporator heat transfer with a fixed metering device. Again, a superheat measurement will confirm that possibility.

Transient high evaporator loads on high temp applications will increase compressor amperage, but I've never seen it increase to the degree your unit is running.

If you can eliminate high head and liquid flooding, I think you should reconsider the electrical possibility, in spite of your confidence that isn't the case. Scrolls will usually start without any "start assist" components. Run some new leads (include the run cap) direct from the compressor to the line side of the contactor, by-passing the start components; start it with equalized pressures and see what happens.

[Butch1234]

thanks for the suggestions.,....on the electrical issues...we installed new capacitors, and start relay, in any case, the measured current on the capcitor leg is only about .5 amp....a permanent capacitor motor needs the 2nd winding to create a rotating field for the rotor to follow...the bulk of the current flow is in the main stator winding...the high current indicates high load on the motor/compressor which I am now assuming is becuase of high mass flow rate (m dot or dm/dt)

we are suspecting that perhaps overcharge may be the issue,,,since we hear a "rattle" in the compressor it appears that we are sucking some liquid into the compressor from the ACC...however, the R22 charge is at the recommeneded level...but many of the recommendations from the manufacturer have been "wriong"

superheat leads back to the amount of charge to some extent ...in the hot water or hot air mode the evaporator is the ground which is about 60+F right now...(pressure is about 110 psi when the system is shut down)...the CPR limits the suction pressure to about 66 psi giving a suction superheat of say 60-38 = 22 F

In the hot air mode the discharge pressure is about 220 psi which is about 110 F and the leaving air temp from the air coil in the air handler is about 85 to 90 (need to measure) which gives a superheat of about 20-25 which means the difference is less than 5 F (25-22) which should be ok if I have figured all this out while I type...howeveer, I still think we have too much R22 going through the system

[KB Cool]

What capacitor has .5 amp? If run? It should be more!!

[koolkahuna]

Okay, let's try this...

What is the full model number and serial number of your compressor?

Copeland scroll right? New?


What is the info on your txv or what type of metering device do you have?


Take and post pictures of these items if it's easier for you.


You state that there has been six(6) compressors fail on this system or five not counting this one...why did they fail?

How old is this system?

Where is this system located?
Not the address but the state, province or region is fine.
I am guessing you are in the UK? I may be wrong...No problem if you are but your power frequency would be 50hz not 60hz then.

When you stated that this was YOUR geothermal system was it for your home or Yours as in your job to solve the current problem?

When you post full answers to these questions, I will share my thoughts on your problem once you obtain professional status here.

Did you apply for pro membership on this site yet?

We have rules that we have to obey if we offer any help to others.

Otherwise there can be possible liability from injury, death or even warranty issues as a result.

So if you wanna play, get legal.
We are interested in solving the problem. That's what we do!

[Butch1234]

yes this is the run capacitor...I may have read the meter incorrectly but that is it...what do you think it should be

[KB Cool]

yes this is the run capacitor...I may have read the meter incorrectly but that is it...what do you think it should be

Way more than .5 amp! If the cap is good the start winding should be drawing several whole amps!!!!