In this interesting condenser fan issue, we noticed that the condenser fan seemed weak and was blowing cold air.
Although we suspected that the compressor may have had an issue, we realized that one of the contactors hadn’t been pulled in when we opened up the panel on the condenser. It was a shunt, so we powered up one side and used meter leads to determine that the contactor itself was working fine.
We already checked the capacitor before the video started, and we had 4.9 microfarads on a 5-microfarad capacitor. The compressor drew less than 1 amp (0.6, 0.4, etc.). Our meter picked up 1.1 amps on the fan wire.
All of the components seemed to check out, so we determined that the fan was backfeeding into the compressor because of the shunt.
We disconnected the power, discharged the capacitor, and found the resistance to ground. Overall, we determined that the condenser fan issue was due to the compressor backfeeding as a result of the shunt. So, that’s why the fan was running without the contactor pulled in.
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Although we suspected that the compressor may have had an issue, we realized that one of the contactors hadn’t been pulled in when we opened up the panel on the condenser. It was a shunt, so we powered up one side and used meter leads to determine that the contactor itself was working fine.
We already checked the capacitor before the video started, and we had 4.9 microfarads on a 5-microfarad capacitor. The compressor drew less than 1 amp (0.6, 0.4, etc.). Our meter picked up 1.1 amps on the fan wire.
All of the components seemed to check out, so we determined that the fan was backfeeding into the compressor because of the shunt.
We disconnected the power, discharged the capacitor, and found the resistance to ground. Overall, we determined that the condenser fan issue was due to the compressor backfeeding as a result of the shunt. So, that’s why the fan was running without the contactor pulled in.
Read all the tech tips, take the quizzes, and find our handy calculators at https://www.hvacrschool.com/.
Learn more about the 2022 HVACR Training Symposium at https://hvacrschool.com/symposium/.
I always walk by and put my hand over the system. This one, i noticed, wasn't blowing that good and it's blowing cold air first thought compressor. Little did i know, and i open the system got a contactor not pulled in so i'm like hmm, okay, of course it's a shunt, so i'm gon na power up one side for you guys across the top bottom of a contactor, it's open, which is good. It's closed contact is working right.
I went ahead and went and already checked my capacitor, the microfarads, it's rated for five, it's 4.9. This is what i found funny. So i got my compressor amp in that six on one i got my compressor amp and a5 compressor. Wrapping the two fan: it's going to be my fan, wire 1.1 contactors not pulled in just to remind you so go ahead and the end starts up higher.
The amp draw is actually higher. When i do check this, i just can't hold the camera. At the same time, so all the components check out good. It's just back feeding from my fan into my compressor, all because of the shunt.
So when i go ahead and i'm just disconnect power go ahead and discharge the cap, i don't know about you guys, but i always like using players. I typically don't wear gloves. Let's go ahead and put it on resistance, i'm using a fluke. 902 fc i'm gon na go ahead and do resistance to ground on my on my fan, so you can see that down in that corner right there.
I got resistance to ground on all of my legs, my windows, so internally, this fan motor is back feeding from the shunt into the compressor and into the fans making it run when the contactor is not pulled in. So this was a fun one yeah. So if you ever come across that make sure you uh check some things to ground thanks for watching our video, if you enjoyed it and got something out of it, if you wouldn't mind hitting the thumbs up button to like the video subscribe to the channel and Click the notifications bell to be notified when new videos come out. Hvac school is far more than a youtube channel.
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A lot of stuff going on here.
Great video. I did not know this was a thing.
I've seen that before! Such a strange problem lol!
What you guys mean to say is not that the compressor or condensor was grounded. They are all grounded if installed according to electrical and safety code. If it were not grounded, your breaker would never trip when you get a ground fault (internal short circuit) from one of the hot legs to the compressor housing. If the condensor unit/compressor were not grounded (according to code) it would be floating electrically, and when the compressor develops a "short circuit" from one of the windings to the case, you would then have an energized chassis at line voltage waiting to shock the next person who leans up or grabs or touches the chassis!!!
For all the "experts" in the comments saying the problem was the "Compressor was grounded" or "Condensor was grounded":… Does an AC unit need to be grounded?
Yes, the case is grounded. If the air conditioner is installed properly and is plugged into a properly grounded 3-prong outlet, no special precautions are needed to ground the air conditioner.
What you guys mean to say is not that the compressor or condensor was grounded. They are all grounded if installed according to electrical and safety code. If it were not grounded, your breaker would never trip when you get a ground fault (internal short circuit) from one of the hot legs to the compressor housing. If the condensor unit/compressor were total ungrounded and floating electrically from earth, you would have an energized chassis at line voltage waiting to shock the next person who leans up or grabs or touches the chassis!!!
This explanation was seriously lacking:
shunt
1. provide (an electrical current) with a conductor joining two points of a circuit, through which more or less of the current may be diverted.
"these components are designed to shunt electrical surges away from microcircuits"
noun
2. an electrical conductor joining two points of a circuit, through which more or less of a current may be diverted.
I'm confused. If power is leaking through to ground to make a complete path for the circuit, wouldn't you get shocked or possibly electrocuted when touching the unit since current is literally passing through the metal of the condensing unit???
Wait, so current was flowing through ground?
If so, wouldn't that blow a fuse or trip the breaker?
Good one! I recently had a cap at a friend's house I changed the cap and the cap must have been so low it reversed the direction of the fan whoever worked on it before, left it like that. And it was running backwards with the new cap I installed. If I hadn't taken a pic before I would not have believed it. Basically i reverse the start and run wires then it ran fine. Service area Barrhaven??
Fan shorted and equipment not grounded
I’ve come across this twice on carrier units. But never looked into why. Thanks for doing that , makes sense. I’ve also had to replace a shunt contactor on a Lennox unit , to quiet it down on shut down. I didn’t believe the tech support , but it did the trick.
I hate shunt contactors. Are you in Ottawa ?
I’m just curious but what would happen if someone got rid of that shunt contactor and stuck a double pole in there instead? Are you in Orleans ?
Compressor current may be flowing thru the compressor windings to the grounded fan motor. Never did like those single pole break contactors.
I think he ment to say "farads" not "farens"
I had one years ago that was grounding the furnace through the line set and would not let the flame bar ground properly. Turns out the ground to the air handler was bad, everything worked fine til the fan motor on the condenser started grounding sending a few volts down the line set and they tried turning on heat. Burn for a few seconds then out. Grounds seemed ok but I finally removed the ground from the furnace to test it and nothing. Open circuit. Then when doing the same for the condenser I found 15 volts to ground between the chassis and ground wire. Checked the ground to another and it was fine. Ran a temporary ground wire from the breaker box to the condenser and 15 volts. Removed the fan motor and problem solved. First time i had seen a fan motor work fine but partially grounding. What a pain in the butt but those jobs test us and teach us lessons we remember forever. Now I check a perfectly fine motor to ground if anything weird happens.
I had this with a crankcase heater issue. Replaced it and issue resolved. Service area Kanata??
I've seen a similar issue a few times but, it was always a grounded compressor. When the contactor closed it would trip the breaker.
This is an awesome tutorial experience thanks for sharing top notch content 👍
I had this happen 2 years ago with a fan lead wire that was pinched underneath the top of the condenser. There was nothing actually wrong with the motor itself, it was just a wire that was shorted to the condenser case.
I've had this happen to me 1 time. I did end up replacing the fan motor and it was resolved.
Would a new two-pole contactor eliminate the back feeding from the fan in this case?
What was the calculus? A bad fan motor back feeding? Or a weak magnet in the contactor ?