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wheelsup 05-03-2012 11:15 PM

HVAC condensor fan outside intermittant
2 Attachment(s)
I've got 2 units and noticed a few days ago, while the downstairs unit cycled on, the air was warm. And got warmer. Didn't get cold quickly. Ran outside and saw the blower/fan motor on top was not turning.

Quickly ran inside, turned the unit off with the T-stat. Went outside, spun the motor by hand, it is smooth. No roughness or binding.

Go inside, flip the unit on with the T-stat, motor outside turns on and runs fine. Inside temps coming out of the duct are around 45F, inside temps around 75F and outside around 70F. Same for the upstairs unit, so the downstairs unit seems to be OK even after running with no blower for 3 mins or so.

I'm new to electrical. Don't know anything save for doing basic wiring and even then I have to follow books step by step.

Took the cover off the unit and looked at the cap - contacts were covered in rust from the fan motor. Aha! I think. Cleaned it off and good to go for 3 days. Now again, tonight, blowing warm air and fan outside is not moving, but you can clearly hear the compressor inside working. So I don't think it's the compressor.

Also - the below cap - I believe runs BOTH the fan and compressor, correct? It's a dual purpose cap? Which is odd that the compressor starts, but the fan does not. Almost makes me think the fan motor might be the issue. I have to replace the cap anyway if replacing the fan motor so might as well replace it but would like to know how to test the cap to see if it's OK. If it's OK then I'll call a tech but my guess is the fan motor is bad.

Thoughts? Where to go from here? Luckily we have two units so I can troubleshoot a bit before calling a pro.

Before cleaning:


Thanks for any help. I'm not very confident with electrical stuff but am willing to learn as I go.

hvactech126 05-03-2012 11:53 PM

Replacing the cap is much cheaper the purchasing a meter to test the cap.

Doc Holliday 05-03-2012 11:53 PM

Nope, it's the cap. Yes, it's called a dual run capacitor. If you have an electrical digital meter that reads microfarads (uf) you can test the cap. A dual run cap shares the common but internally herm and fan are individual. Happens all the time, one side will fail and the other will still be good.

Two ways to go about reparing this, either one new dual run cap of the same size or one single run cap for the fan, usually 5 mfd (uf).

The fan cap will be less expensive than a new dual run capacitor but will require an extra wire to jump from the common from the old cap's common to one side of the new fan cap. The fan wire will go to the other side of the fan cap.

Doc Holliday 05-03-2012 11:58 PM

Btw, don't go sticking your fingers in there with electricity to it, Also, discharge any possible electricity stored in the cap (with power off first to the unit) by sticking a screwdriver across the poles and even then don't touch the prongs with your fingers. Just not good practice.

wheelsup 05-04-2012 12:25 AM

2 Attachment(s)

Originally Posted by Doc Holliday (Post 914079)
Btw, don't go sticking your fingers in there with electricity to it, Also, discharge any possible electricity stored in the cap (with power off first to the unit) by sticking a screwdriver across the poles and even then don't touch the prongs with your fingers. Just not good practice.

Thanks Doc.

Is it OK to short out the cap with the wires still on? I flipped the breakers for the unit but wasn't sure about shorting the cap. Can you short it out by laying the screwdriver across all combinations of the poles? Should you unplug the wires connected first? Or is there a way to do it? IIRC I have two yellow wires on one side, one to the fan, one to the relay, one brown, and one blue to I have no clue.

Here is my cap. I found a similar one on Grainger so I will be ordering shortly. As luck would have it I leave for 4 days tomorrow so my wife will just have to use the upstairs one while I'm gone over the weekend.

If I read it right, I'm looking for a 35/5 370v cap? $30 shipped not bad

Would this one work as well? I have a Gringer local to me so I could pick it up:

wheelsup 05-04-2012 12:53 AM

Also, one pole should be marked "Herm" which is the blue wire - runs the compressor. One pole marked "fan", brown wire. The other pole is unmarked but should have the two yellows plugged into it, correct?

EDIT: Searched some more, found my answers, damn learning a lot thanks guys.

REP 05-04-2012 01:42 AM

Yes the cap you have picked out is the correct one a 35/5 370volt.
Hook it up the same as the old one.Caps are cheap and even if you need a motor you always change the cap when you put new motor on.
If you find out it dosen't solve the problem then you will need a new motor and reuse the new cap.
While you have everything open and are working on it,you might just as well clean the spades on the contactor too.
you should have no problem so good luck.

wheelsup 05-04-2012 07:56 AM

Bought a new cap. New one tests 36/5. Old one tests 30/5. The 5 is the fan. So it appears as thought the cap is not the problem for the fan, although it does need to be replaced because it's out of spec on the compressor side. Any ideas how to test the motor? Is there a way?

I don't like throwing parts, and don't want this to continue as it will overheat if it goes unchecked. My main concern is getting it fixed.

Anything else this could be? I will be calling a pro to come look next week, I don't really want to buy a new fan motor if I don't need to. Would rather spend the $$ to troubleshoot then replace if needed.

Doc Holliday 05-04-2012 09:51 AM

Nope, bu you would've needed a new cap for the new motor regarldess.

Sorry to hear that, it certainly sounded like it was the cap and not the motor. But don't worry those motors are something like $50-$100 so not expensive.

wheelsup 05-04-2012 08:11 PM


Originally Posted by Doc Holliday (Post 914200)
Nope, bu you would've needed a new cap for the new motor regarldess.

Sorry to hear that, it certainly sounded like it was the cap and not the motor. But don't worry those motors are something like $50-$100 so not expensive.

Here is my fan motor.

Just curious though, how do we know it's the motor? Nothing really much else to point to at this point, since the compressor comes on (ie replay/contactor)? Just curious if you think there is anything else to check before replacement.

Doc Holliday 05-04-2012 08:55 PM

I get that same motor for $50-$70. It's a very common 1/2 hp 1100 rpm used in many condensers. It's Grainger you're buying from, why it's so expensive. Plus you're not an hvac contractor so your prices are different.

When a motor is recieving voltage but not coming on then there's nothing else it can be. There is only the contactor which feeds one leg of power and the other leg fed through the capacitor.

There is nothing else in between.

Doc Holliday 05-04-2012 09:01 PM

You can use a 1/2 hp 230v 1075 rpm motor as it's cheaper and more common. 25 rpm less will not affect anything. We do it all the time, install 1075's instead of 1100.

wheelsup 05-07-2012 03:06 PM

Hey Doc I appreciate the responses. Just wanted to let you know I'm not leaving everyone hanging. I scheduled an appt for Wed for a pro to come out and take a look, but have also ordered the fan and another cap. I went with the OEM fan. To save $50 at most and not be able to just swap in the fan that is an exact fit made me nervous - if the motor is the culprit I'm already saving a few hundred I would guess doing it myself so I got that going for me.

Anyway the pro is coming on Wed so I will report back what he says, also checking the general health of the system which I like as well. If it is the fan I'll swap it and the two caps in and hopefully get some more life out of the system.

I am also thinking of replacing the other units fan motor as well just for preventive mx - I don't want it to fail and overheat the compressor and cause it undue stress. Any thoughts to that? Or a waste of $$ as it could go for another 5 years?

wheelsup 05-09-2012 02:02 PM

OK service tech came out today. Did a good job. Checked everything over and unit is running OK no issues with compressor and evap coil upstairs.

Said, like Doc said above, only thing it could be is the fan motor. I picked up an OEM motor from Grainger today and swapped it in, and replaced both of the capacitors on both units.

He did check the amp draw on the original motor, and said it was fine, and I ohm checked it when I got it out. 165, 120 and 45 so they all add hopefully I didn't just replace a good motor...

I suppose I could've replaced the cap and ran with it but I didn't want to take a chance of it going out again and damaging the compressor. Here's hoping it fixes the problem!

wheelsup 05-18-2012 12:42 AM

Carrier heat pump -> intermittent fan -> possible circuit board issue?
1 Attachment(s)
OK guys need some real help here as the local companies aren't helping much - nothing is getting fixed!

Previously posted about an intermittent condenser fan issue.

Tech diagnosed as bad motor, I replaced cap and motor with OEM.

Unit ran fine for a few days from what I could tell.

Then tonight, I watched the condenser fan motor turn over by itself on startup.

Almost exactly 15 minutes later, the fan stopped (hot air blowing out vents). I went out and spun it - it spins freely no binding whatsoever.

Turned unit off, turned unit on, no start on fan.

Unbuttoned unit, took power off (at breaker panel) for tstat and for unit. Unit has a separate 20 amp breaker, tstat is on the electric heat strips with a 50 amp breaker.

Poked around a few mins, put breakers back on, and condenser/compressor runs just fine!

Poking around on the circuit board my hands touch a resistor that is absolutely HOT to the touch (see pic). 150*F using an IR temp. gauge.

I'm fortunate that I have two units of the exact same kind. I turned my other unit on, resistor is showing around 65*F. Clearly an issue here.

Turned breaker off for unit. Resistor still HOT and staying that way. Turned tstat breaker off, resistor still HOT and staying that way. Ohm check is bad, shows 2 ohms (should be 330 +/- 10%).

Unplugged the board, tested resistor again, noticed it was now COLD and tested within spec (325 ohms).

Pluged board back in, breakers both still off, tstat verified off (no display) and resistor is getting hot again! It is getting power even though the breakers are OFF!

WTF is going on here?

Other unit's resistor remains cool while on and tests fine with breakers ON and the unit turned off (342 ohms). Thoughts? A circuit board issue or an electrical issue? Unit has been run for approx 7 years. Getting late I'm going to swap boards between the units tomorrow...they look the same. Should be OK right?

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