Basement Heat Pump High Pressure Switch

I replaced my original basement heat pump about 10 months ago with a new model 46515-811 ...an exact fit. The new unit has worked great, being used about 50% of the time since installation. Then yesterday I switched the unit on while doing some chores. First compressor started fine, but when 2nd tried to start it tripped the Surge Guard. Tried again, same thing. I had some trouble a month or so ago with my 50a circuit. This time it checked out fine but I changed to 30a, and then to generator just in case. On both 30a and generator the 2nd compressor simply failed to start.

Long story short, today I found the problem was the high pressure switch for #2 was tripped. Re-setting it restored normal operation.

Why would the high pressure switch trip? ...unit is clean, has good air flow, blowers are running as normal.  And why would the switch being tripped trip the Surge Guard?

We do not know the answer, just thinking/wondering out loud.
Is this high pressure switch a manual reset switch? Many times they are auto reset, when the pressure gets low enough.
I presuming your surge guard was tripped either by high current or low voltage. Locked rotor on compressor 2 might cause either.
I do not know if this system has 1 or 2 condenser circuits. Would think there would be no high pressure on start up unless there was a blockage in the condenser circuit. Yes I have seen it.

You mentioned previous trouble with your 50 amp circuit. Is it possible a similar problem has resurfaced. I believe the two compressors are on separate legs of the 50 amp service, so possible compressor 2 is on a troubled leg.
Just trying to give food for thought.

High pressure switch is a manual push-to-reset. I have to open a screwed shut basement door, then remove the cover to the electronics box to get to it ...minor hassle but not a big deal.

No locked compressor since it is again working after resetting the high pressure switch. I am pretty sure each compressor has it's own condenser circuit running the same condenser.

It is altogether possible there is a problem with the 240/50a shore power circuit. Power company found a bad neutral connection on top of the riser where aluminum wire hooks to copper. They redid that connection and it now reads good with my multi-meter where it did not before ...both times those readings were w/o a load so something may be happening when it gets loaded up. We will be hitting the road for a month in about 10 days so great opportunity to see how it does on several RV park shore power connections.

Paul, I know this is an old post but I?m having similar problem now with compressor 2.
When starting, it hums and trips out on the overload.
Have changed capacitors no change. Pulls about 60A but doesn?t trip breaker, o/l goes out.

Have metered what I can without pulling unit, common to start winding, common to run and start to run.
Common to start and common to run resistances added together are real clost to start to run resistance.

My question is, I didn?t see any resets. 
Would you recall where the reset is?
Thanks in advance

Bob

If the compressor is pulling 60 amps while trying to start, I would NOT think it was a tripped switch. Sounds to me like a capacitor is not producing up to par, bad connection in the start winding wire, or maybe a stuck or locked compressor. If you have an amp meter, try taking a reading on the start winding wire, while trying to start (same situation as when you saw the 60 amp load except on start winding wire, if you see anything, probably the wire in connected). Then I would think, either capacitors not producing up to par or stuck compressor. If the compressor is stuck,  I have held a larger capacitor in the circuit, just long enough to give it a start jolt and disconnect it as soon as it started, let it run for a few minutes to get the oil circulated, then it would start thereafter as it was supposed to.

Thanks Neal..
I am sure I can rule out capacitor, new installed and I swapped #1 for #2 caps. Compressor 1 started and 2 did same thing.
You?re suggesting to clamp the start winding while trying to start but not sure I am understanding what you are saying ?if you see anything the wire in connected.?  Am I correct assuming you meant if I see anything the wire is connected? What amperage would you expect to see on start winding?

I did put a 40Mfd 370VAC cap in on run, should be 30 but I had one in tool box and thought I would give it a try even though run cap should be 30Mfd 370VAC. No change.
Start compressor does have hard start relay on it.

Right now I?m thinking compressor is locked up but common, start and run combinations have me questioning myself.  Have not taken unit out, readings taken from cabinet that?s accessible from front. I can?t see that being an issue.  Not knowing what resistances should be on windings, I compared to good compressor and both units real close.

Not sure if you?re A/C trade (I?m not, I?m electrician) but from your experience could it be locked up due to bad valve?

Appreciate any guidance

Bob

Bob T said:

Thanks Neal..
I am sure I can rule out capacitor, new installed and I swapped #1 for #2 caps. Compressor 1 started and 2 did same thing.
You’re suggesting to clamp the start winding while trying to start but not sure I am understanding what you are saying “if you see anything the wire in connected.”  Am I correct assuming you meant if I see anything the wire is connected? What amperage would you expect to see on start winding?

I did put a 40Mfd 370VAC cap in on run, should be 30 but I had one in tool box and thought I would give it a try even though run cap should be 30Mfd 370VAC. No change.
Start compressor does have hard start relay on it.

Right now I’m thinking compressor is locked up but common, start and run combinations have me questioning myself.  Have not taken unit out, readings taken from cabinet that’s accessible from front. I can’t see that being an issue.  Not knowing what resistances should be on windings, I compared to good compressor and both units real close.

Not sure if you’re A/C trade (I’m not, I’m electrician) but from your experience could it be locked up due to bad valve?

Appreciate any guidance

Bob

Click to expand...

The reason I said anything (amps) on the start winding is because it may vary from compressor running or not running. Also we have been retired 15 or more years, so not sure I remember everything correctly. I think a 40 MFD capacitor might register around 8 or 9 amps when compressor is running, but might not till it gets up to speed. Can't remember. Also if the start capacitor is a time unit (electronic) rather than a start relay type, you might see the amps on the start winding first go up to whatever (run + start) then fall some (run only when the start falls out). Most times the start will be 2 to 4 times the run capacity. We would normally check start capacitor operation by clamping the amp meter around the start capacitor wire only, start the compressor and watch the amps jump up, then quickly fall out.

If I thought it was locked up, I would try with maybe a 100 up to 200 MFD start  capacitor and connect one wire at  compressor run capacitor common post, while holding the other wire by hand on the run capacitor start winding post, watch meter clamped on compressor contactor wire and turn it on. The meter should tell you if the compressor is running or not. Remove your hand held capacitor wire within 2-3 seconds whether it starts or not.  I have seen this start many frozen compressors.

Good luck,

PS I have seen quite a few NEW, bad capacitors.

I guess there are exceptions to every rule. My first thought was that if you see any amp reading on the start winding, it would confirm a connection to the compressor, but it could be possible the wire was burned off at the compressor terminal and shorted to the compressor cabinet, which might still give you a reading on the start winding.

You could also OHM all your wires to ground. If anything shows a connection to ground, you have to locate that problem. Would think you would see more than 60 amp draw if that were the case.

Sorry, we did not answer all your questions above.
Yes it is possible to be locked up from some broken compressor component.
It is also possible to momentarily reverse the compressor by swapping the RUN & START winding leads to the compressor. Not sure we ever did that on a scroll compressor or what the consequences might be.

Neal, once again thank you for sharing your knowledge.

Interesting idea of reversing start/run windings.  Not too sure I want to give that a shot just yet.
I?ve got a old trade school book at home that 35+ years ago was considered the bible for motors of all kinds. Can?t remember if compressors were in it or not but would probably help me to visualize what I?ve got going on here. I think I will see if I can locate it while home.

We are moving this week (further south), heading home for monthof December (Christmas) and hopefully after everything settles down again in January  I can check your suggestions.
Will let you know what I find.

Hope you have a great Thanksgiving.

All the best

Bob

I believe my problem in 2017 was a clogged filter. I believe it tried while running the heat pump months before I found was a problem. AC sign of clogged filter would be coils freezing over.  As already mentioned. I have had a locked compressor cause your problem. AND, I had a broken blower support jam the blower and prevent it from starting,  which I believe will by design prevent the compressor from starting.

Thanks Paul
Both inside and outside blowers run well, no slow starting.
Inside coil did have some dust on it but that was looked after with a vacuuming using brush.
Regularly spray down outside coil.
Have everything related to compressor 2 isolated now at breaker.

Thanks for info.

Bob