Carrier AC condenser motor is intermittent

[oldmanbob]

Apologies in advance for the lengthy post... but I figured it may eliminate questions and help for a quicker diagnosis.

I have a HVAC carrier model 38cks. I have two of these units side by side, one for 1st floor, the other for the 2nd floor. I had to change the capacitor on the same one a year ago… the top of the capacitor was expanded outward, like a can of soda that was about to explode. Unit has worked fine since. I have a thermostat that seemed iffy as well, but all has ran fine.

Fast forward to just one month ago, it got real hot upstairs. I check the outside unit and the fan is not turning. I tried the fuse panels a few times, checked the thermostat, and no luck. I looked under the service panel and looked at the physical appearance of the capacitor (GE model 97f9834). No bursting at the seams as noticed on the previous capacitor that went bad. So I decide to check voltage.

This is where I really struggle. Using a voltmeter and where and what to test .I put a voltage tester to what I think is correct and all seems ok. I tested where I thought I should be getting voltage. On the outside unit, the wires come into it. The green wire seems to go to ground right against the unit itself. The two other wires, which I believe are hot connect to something the schematic drawing labels: “CONT”. I have no idea what that means. But it is a little plastic looking black box type item that has a few wires, blue, black yellow couple of yellow wires and a black wire going from it. It has two yellows coming from it… one I think to the compressor, and the other to the capacitor. This seems to be the only hot wire to the capacitor. Using a voltmeter, when I touch one lead of the voltmeter to the incoming yellow and the other black lead of the voltmeter to the unit (ground) the voltmeter reads 120 or 121. it also reads the same on the other yellow, as well both other wire connection on the top of the capacitor where the brown and blue wire connect to the top of the capacitor. All read 120, but seem a little rusty on the tabs coming on top of the capacitor. But I hopefully concluded the capacitor is fine. Sorry for the painful descriptions, but I have no knowledge on correct terminology. I would have called an HVAC company but I am still looking for a job and dollars are tight.
I put the service panel back on and go inside to search the internet for suggestions. ½ hr later, I go back outside and the darn fan is running. In a couple of hours, my home is now very cool and comfortable upstairs and downstairs. I then concluded I had a faulty thermostat that was iffy. But as long as everything worked, I left it be.
Today, the unit quit again. It got up to 87 degrees upstairs. I killed power and replaced the thermostat. That was easy as I had all wires labeled correctly before starting. The fan outside was still not turning.
With power off, I removed the service panel. The capacitor looked fine. The fan blade turns easily by flicking it. No noise is heard not nor is any resistance felt when manually spinning the fan blade. I hit power on and check all plugs on top of capacitor, all seem to have correct voltage. I took my digital camera to gets pictures of all wiring and all behind the service panel so I have a record of what is there. I put service panel back on and turn on breaker. No luck. I take the model number of condenser fan motor and go back to internet. I spend an hour or so and find some info on replacing fan motor but get confused to continued references to motherboard and contactor. I do not know where theses two items are to check for any loose wires, etc.

I decide to go back outside, kill power and remove leads from capacitor and use a small emery board on the capacitor metal wire leads to remove the rusty connections. When I get to unit, the fan is spinning!!! Cold air is coming from all vents upstairs. I killed power and still used emery board to try and clean contacts. Fan came right back on when power was restored and is still going strong. I was also considering changing out the capacitor even though the voltage on all leads seemed fine. When the first one went out a year ago on this same unit, it was on a weekend and I had to go without for a day until I could buy a replacement capacitor. So I bought an extra capacitor last year just in case. I have two units that it fits, I was employed then and the extra 40 bucks for an extra capacitor seemed a reasonable cost in case a capacitor died again.
So this is where I am at. I have a unit now working again, but has stopped twice without reason in the last 30 days or so. I can’t trust it as I do not know if or when it may stop again. Hopefully some of you can give me a suggestion or two. The fan motor alone seems to run about $200 but I do not know if I can buy one at a supply house as I am not a licensed HVAC technician.

Should I check this “motherboard” or the “contactor” , if so, how and where are they. Should I bite the bullet and call an HVAC company and put more on my charge card? It is supposed to be in the 90’s or higher degrees all week and summer has not even started. Here the info on my unit. Carrier model 38cks, capacitor model is GE 97f9834, and condenser fan motor i9s a ¼ hp motor but the label has two different numbers that come back to a fan motor : Carrier 5kcp39egs070s and Cpn hc39ge237a, I just figure if the cost wholesale is 175 to 200, then by the time an HVAC company charges me a trip and diagnosis fee, their up charge on the motor and then labor cost .. my guess is 500 to 600 dollars service call on my 7 year old ac unit.
Thanks in advance or any and all suggestions or ideas.
Bob

[paul52446m]

Apologies in advance for the lengthy post... but I figured it may eliminate questions and help for a quicker diagnosis.

I have a HVAC carrier model 38cks. I have two of these units side by side, one for 1st floor, the other for the 2nd floor. I had to change the capacitor on the same one a year ago… the top of the capacitor was expanded outward, like a can of soda that was about to explode. Unit has worked fine since. I have a thermostat that seemed iffy as well, but all has ran fine.

Fast forward to just one month ago, it got real hot upstairs. I check the outside unit and the fan is not turning. I tried the fuse panels a few times, checked the thermostat, and no luck. I looked under the service panel and looked at the physical appearance of the capacitor (GE model 97f9834). No bursting at the seams as noticed on the previous capacitor that went bad. So I decide to check voltage.

This is where I really struggle. Using a voltmeter and where and what to test .I put a voltage tester to what I think is correct and all seems ok. I tested where I thought I should be getting voltage. On the outside unit, the wires come into it. The green wire seems to go to ground right against the unit itself. The two other wires, which I believe are hot connect to something the schematic drawing labels: “CONT”. I have no idea what that means. But it is a little plastic looking black box type item that has a few wires, blue, black yellow couple of yellow wires and a black wire going from it. It has two yellows coming from it… one I think to the compressor, and the other to the capacitor. This seems to be the only hot wire to the capacitor. Using a voltmeter, when I touch one lead of the voltmeter to the incoming yellow and the other black lead of the voltmeter to the unit (ground) the voltmeter reads 120 or 121. it also reads the same on the other yellow, as well both other wire connection on the top of the capacitor where the brown and blue wire connect to the top of the capacitor. All read 120, but seem a little rusty on the tabs coming on top of the capacitor. But I hopefully concluded the capacitor is fine. Sorry for the painful descriptions, but I have no knowledge on correct terminology. I would have called an HVAC company but I am still looking for a job and dollars are tight.
I put the service panel back on and go inside to search the internet for suggestions. ½ hr later, I go back outside and the darn fan is running. In a couple of hours, my home is now very cool and comfortable upstairs and downstairs. I then concluded I had a faulty thermostat that was iffy. But as long as everything worked, I left it be.
Today, the unit quit again. It got up to 87 degrees upstairs. I killed power and replaced the thermostat. That was easy as I had all wires labeled correctly before starting. The fan outside was still not turning.
With power off, I removed the service panel. The capacitor looked fine. The fan blade turns easily by flicking it. No noise is heard not nor is any resistance felt when manually spinning the fan blade. I hit power on and check all plugs on top of capacitor, all seem to have correct voltage. I took my digital camera to gets pictures of all wiring and all behind the service panel so I have a record of what is there. I put service panel back on and turn on breaker. No luck. I take the model number of condenser fan motor and go back to internet. I spend an hour or so and find some info on replacing fan motor but get confused to continued references to motherboard and contactor. I do not know where theses two items are to check for any loose wires, etc.

I decide to go back outside, kill power and remove leads from capacitor and use a small emery board on the capacitor metal wire leads to remove the rusty connections. When I get to unit, the fan is spinning!!! Cold air is coming from all vents upstairs. I killed power and still used emery board to try and clean contacts. Fan came right back on when power was restored and is still going strong. I was also considering changing out the capacitor even though the voltage on all leads seemed fine. When the first one went out a year ago on this same unit, it was on a weekend and I had to go without for a day until I could buy a replacement capacitor. So I bought an extra capacitor last year just in case. I have two units that it fits, I was employed then and the extra 40 bucks for an extra capacitor seemed a reasonable cost in case a capacitor died again.
So this is where I am at. I have a unit now working again, but has stopped twice without reason in the last 30 days or so. I can’t trust it as I do not know if or when it may stop again. Hopefully some of you can give me a suggestion or two. The fan motor alone seems to run about $200 but I do not know if I can buy one at a supply house as I am not a licensed HVAC technician.

Should I check this “motherboard” or the “contactor” , if so, how and where are they. Should I bite the bullet and call an HVAC company and put more on my charge card? It is supposed to be in the 90’s or higher degrees all week and summer has not even started. Here the info on my unit. Carrier model 38cks, capacitor model is GE 97f9834, and condenser fan motor i9s a ¼ hp motor but the label has two different numbers that come back to a fan motor : Carrier 5kcp39egs070s and Cpn hc39ge237a, I just figure if the cost wholesale is 175 to 200, then by the time an HVAC company charges me a trip and diagnosis fee, their up charge on the motor and then labor cost .. my guess is 500 to 600 dollars service call on my 7 year old ac unit.
Thanks in advance or any and all suggestions or ideas.
Bob

When the unit won't run check and see if the out door fan motor is hot, if it is the motor might be cutting out on internal over load. The motor is made to run at a certain temp. if it heats up , there is a internal thermo heat switch that will turn off the motor. Over amping can cause this. Also a bad run capacitor can make it over heat. If the fan motor turns off then the compressor can get hot and turn off on internal overload. When a sealed motor cuts out, it takes a long time to cool down and restart. Paul

[oldmanbob]

Paul, thanks for your input. The fan ran all night (thankfully) but quit again this morning. I don't know how long it had stopped running, but when I was aware of it. I borrowered my neighbors Fluke infared temp sensor, and measured the temp of the motors. The motor on the unit that was not running was 85 degress, while the twin unit which is for my downstairs (I have two units outside) the downstairs unit was runing fine and its fan housing temp was 113 degrees. All I could check is the outside fan housing temp as the fan is sealed. The opne that was running was considerably warmer than the one not working. I wonnder now if the compressor was still too hot, per your suggestion. I do not know how to check that.

I then ran to do an errand and came home3 hours later and the fan is still not kicking on at all. I took the extra new capacitor and unplugged the one currently on the unit and plugged in the new one and let it hang side by side and threw the breaker back on... still no fan.

My next thought (I'm running out of ideas) is to remove and swap the fan condenser motor with the unit that works fine. As they are identical units, this should hopefully clear up whether it is the fan or not... but my problem is that I do not know how difficult it is to remove and re install condenser fans motors, but I am about to find out. I will first cehck you tube and see if any videos on the subject are there.

Thanks for you feedback and if you have any more suggestions, I am all ears.
Thanks, bob

[oldmanbob]

found root cause

Found that the relay was not working on the contactor so we removed it and cleand uo the contact points with steel wool; still no change in problem, but when attempting to hook up thermostats leads bck to contactor we (son and I)noticed no power coming through and it should have been 24 volts. That lead us back inside to the new thermostat I installed. I had assumed it was working becuase of the readout and the fact it did cool last evening, but a quick check showeed no power to thermostat. (the readout was from the installed batteries in the thermostat) , thus we then had to take a trip to the 130 degree attic where a barrage of multimeter tests were conducted.

Finally traced down the root cause... the single piece of sheet metal that held the cover door safety switch had bent a little and the safety switch was not closing all the way, thus not allowing current to the thermostat and so on and so forth. The safety switch is mounted on a small bend of sheet metal. Thus a little jury rigging to make sure the safety swicth stayed closed when cover is on took care of the problem. We also ensured that the safety switch still triggers when cover is off. Problem solved and total cost was time, a lot of frustration and sweat, and a cost of a new programmable thermostats (85.00) that I probably did not need.

but thanks for your help and your ideas. I still learned alot. And as today is Memorial Day, to any and all service members who may read this post soon or in the years to come, God Bless you and thank you for your service!

[HayZee518]

what you might check later down the line is to use a well insulated screwdriver to test the capacitor. jump from the COMMON terminal to either side. You will get a hefty spark if the cap is good.