Heat Pumps and Electric Heating - How to check compressor start cap?

Goodman heat pump, was heating well last month. Evap and condenser fans run, thermostat shows cooling mode engaged, but compressor not running. :madhell:
Relay (contactor?) points appear closed, but compressor not happening. Has freon (guage shows pressure correct for ambient temp:D). How should I check the compressor start cap and what else should I look at? (Didn't verify power actually passing points with meter, doh! :wall: But can see typical "brownout" in house lights as compressor tries to kick in. Now that I think about it, "brownouts" were more pronounced last few months when compressor kicked in for heat, symptom of failing capacitor? :thinker:)

You chk a cap with a meter that reads mfd, make sure cap is good first. If it is and you have power to comp and it still won't start need to check comp for shorted/grounded windings

You chk a cap with a meter that reads mfd, make sure cap is good first. If it is and you have power to comp and it still won't start need to check comp for shorted/grounded windings


Any advice on how to find the spec (amount of microfarads?) I should be checking against or general spec for starting caps? What should the resistance reads be on the compressor before I declare them shorted?

There should be documents inside the cover on outside unit. Most units today have a combo cap unit for compressor and fan. I know the fan is around 4 to 6 mfd. The compressor is higher but it should be under the access cover. Look at the connection end and see if it is bulged and if so replace it. Make sure all power in panel and disconnect is off. To check for short find the power leads from relay and isolate from fan leads. Check to ground and should be an open. Across the motor itself will be a low resistance but with and accurate low reading ohm meter should see some resistance. Not sure but very low. My old unit one side had shorted internally and blew the breaker. If the cap is bad the motor will not start and should trip out from heat overload if you are lucky. You may want to get a Tech to look at it if you are not comfortable with elecricity. If the fan is runing the relay should be OK.

The mfd should be on the cap though it may be tuff to read.

For the comp. take an ohm reading between commen and start terminals then between commen and run. Those two values added together should equal the value you read between start and run:coffee:

Dang thing don't even have a start cap. The second cap I saw is actually for the fan:wall::o. So, to start all over, would the run cap keep the compressor from starting? I can hear it try, but it just don't "kick in". I can see it "load down" the lights in the house like it always does when the comp starts, and it was doing that even more noticeably than usual when in heat mode the past few months. 4 ohms on what is shown as "AUX" winding on comp, 8 ohms on "MAIN". None short to ground.:confused:
How much does a cap cost in case I wanna "diagnose by parts replacement"?

Yes the run cap can keep the comp from starting, thats the cap we have been talking about, you can get one for about $10.

As far as windings go, re-read previous post

P.S. If this was a transit bus, I'd be done by now, but belt drive compressors are SOOO much easier to diagnose.Beer 4U2

Yes the run cap can keep the comp from starting, thats the cap we have been talking about, you can get one for about $10.

As far as windings go, re-read previous post

TEN BUX??? If I'da even dreamed it would be that cheap, I'da never bugged y'all. "Diagnosis by parts R&R" it is, then.

Read 8 ohms on main to common, 4 on aux to common, open both to ground, never thought to go main to aux.

Run or Start it's the same in these things. Yours apparently has separate ones. If the cap does not help you may have to install an auxilary start kit. As they age some need the extra kick. I have seen some put on when just replacing the original cap was all that is needed. Resistances look as if they may be OK. Good Luck.

this just gets better and better. only place I could find a cap it was 30+$ because johnstone doesn't sell to the public anymore. :madhell:
that didn't get it running. found bad terminal on meter, correct read on coils is about 1.3 and 1.7 each, across both a little over 2, neither is shorted to ground.
will see if grainger has a start kit in stock. des it come with instruction even a grease monkey like me can follow? :p

this just gets better and better. only place I could find a cap it was 30+$ because johnstone doesn't sell to the public anymore. :madhell:
that didn't get it running. found bad terminal on meter, correct read on coils is about 1.3 and 1.7 each, across both a little over 2, neither is shorted to ground.
will see if grainger has a start kit in stock. des it come with instruction even a grease monkey like me can follow? :p


Graingers has hard start kit in stock. (turns out they had cap in stock, too --for 11.00$:madhell::wall:)

Wife forgot to pick up hard start kit, now waiting till Monday to find out if it works.
Anybody want a good used cap free?:cool:

Does your meter have capacitance checker? If not take your old one and drain it by shorting the terminals out. Then take your meter in the resistance and connect to terminals. Should show a near short briefly and then charge up to a high resistance and will increase as it charges to meter battery. If it shows a low resistance then it is leaking but if no charging then it is open. The best test is meter with a cap section which even cheap meters have today. Of course you have put in a new one for now. Does the compressor hum and then stop as if the overload tripped and then after a period of time try to start again? Also have you verified that the power voltage is at or near 220-230 VAC? I had overvoltage situation about 6 months before old HP shorted out. Line voltage had gotten as high as 280 volts and light blubs were popping all over the house. Power company fixed the situation but about 6 months later the compressor shorted on one side to ground. Of course this blew the breakers out. I got 22 years out of it. If hard start kit does not work then you may consider a HP TECH to look at it. Usually when a aux start kit is needed the compressor will not start at first, OL kicks and when OL resets it will hesitate and then start most of the time. You may have a bad compressor.

Does your meter have capacitance checker? If not take your old one and drain it by shorting the terminals out. Then take your meter in the resistance and connect to terminals. Should show a near short briefly and then charge up to a high resistance and will increase as it charges to meter battery. If it shows a low resistance then it is leaking but if no charging then it is open. The best test is meter with a cap section which even cheap meters have today. Of course you have put in a new one for now. Does the compressor hum and then stop as if the overload tripped and then after a period of time try to start again?
Yes, exactly.

Also have you verified that the power voltage is at or near 220-230 VAC?
Yes, 220 @ both main and aux on comp.

I had overvoltage situation about 6 months before old HP shorted out. Line voltage had gotten as high as 280 volts and light blubs were popping all over the house. Power company fixed the situation but about 6 months later the compressor shorted on one side to ground. Of course this blew the breakers out. I got 22 years out of it. If hard start kit does not work then you may consider a HP TECH to look at it. Usually when a aux start kit is needed the compressor will not start at first, OL kicks and when OL resets it will hesitate and then start most of the time. You may have a bad compressor.

Hard start kit installed today, no joy.:(

It tried to start a couple times like before, then all stopped, even condenser fan, and smoke appeared to come from defrost relay.:thumbdn:

Now even with thermostat in "off" position, contactor is closed and condenser fan tries to run (turns very slow).:wall:

Time for new unit.:madhell:

Any advice on finding contractor who would let me install, and them do the freon charge?

I really like this guy's attitude & ideas (especially the TXV thing).
heat pump repair and service without cost of replacement (http://www.toad.net/~jsmeenen/heatpump.html)

And who has the best price on a new unit?