Home HVAC: Should Condenser Fan Ever Stop?
 

I noticed yesterday that my condenser fan wasn't running at one point, although the compressor sounded as if it was running. I panicked and ran inside and shut everything off, then when I went outside about a minute later, the condenser fan was running. It was spinning smoothly, no bearing noise or anything abnormal.

Is this behavior normal? Should the condenser fan ever be stopped while the compressor is running? I always thought the two turned on at the same time.

BTW, the A/C works fine, blows cold air. I just want to be safe...

You'd better keep a close eye on that. I don't think it should ever NOT be running when the compressor is. Given long enough, the condensor temp and pressure will rise causing problems. Most have a high side limit switch or valve that will open.
It happened at the house last yr when a wire came loose on the fan motor. Compressor made all kind of racket. Scared the hell out of me. I still wonder what damage, if any, was done. Seems to work ok though.

Thanks for your feedback - that's exactly what I'm thinking. That's why I panicked and ran inside to shut it all off. Late last night it got so humid in the house that I went ahead and switched the A/C back on. I went outside to check, and the fan was indeed spinning this time, with hot air blowing, so it appeared to be working fine.

Maybe some of the other experts here have seen this happen before? Should I remove the fan and check the wiring? Or is there a circuit board that controls the fan which I should be inspecting instead?

The most probable cause is that the bearings are going bad in the condenser fan causing it to sieze up and trip it's internal overload or, it's overheating (either bearings or electrical) and tripping the overload. You should plan on replacing that condenser fan motor in the near future because either way, it's on the path to failure.

Used to, fan motors had oil ports on them and you could ressurect a motor with marginal bearings for a season or two. The last couple of times I've messed with fan motors they didn't have any oil ports.

Thanks for the tips - seems to make sense. Except I am wondering, if the fan motor was overheated and/or some sort of overload breaker was tripped, how is it that the fan started spinning when the A/C panel was switched off?

BTW - I checked the fan for oil ports and did not find any. Where can I pick up a new fan motor? Does it come with the blades or do I just transfer them over?

It is possible that the condenser fan is thermally controlled. The way to determine this is to look at the condenser control diagrams, which will show any ambient temperature-related switching in line with the condenser fan.

If there is no thermal control, I would suggest that you look for a loose connection that could cause the fan to run intermittently, and otherwise appear to be just fine when it is running ...

Thanks, Jim H - another dumb question: Where do I find such a condenser control diagram? Should it be printed somewhere on/in the unit? Or do I need to look up the make/model and see a HVAC supply store? Will they work with a non-pro?

I would check Grainger for a new condenser fan. Buy it with the blades. It's not much more expensive and you'll save yourself a lot of trouble. Those blades are not easy to remove sometimes.
Other than that try the yellow pages.

As far as the fan look for a diagram pasted on the back of the cover or folded up inside.
Get a multimeter and take amp readings and compare it to the rating on the motor. Then check for loose connections. Also check the contactor the contacts may be corroded. A new contactor should cost around $10 or so.
You could have a bad capacitor which could explain the delay in getting started.

Danny

Awesome info from everyone here - THANKS! I'll probably be fiddling with it tonight and will report back. Thanks again!

You're shutting off the 220v at the breaker before messing around with the condensor, right?

Should be able to tell if the fan motor is going by giving it a spin and checking the bearing smoothness and/or checking for side-to-side play in the shaft. If the fan is obviously on the way out, the low risk thing to do is shut down the unit until it is repaired. Running the condensor without the fan will cause other problems. Don't ask how I know this.

Another possible source of parts in town is "Adam the Answerman." Small business on Plano Rd. near LBJ. They mostly do appliance stuff, but I've purchased start capacitors there as well. Good little place.

- JimY

Just thought I'd post another observation. I haven't opened it up yet (gonna do that tomorrow), and had the wife power it off around lunchtime. However a few minutes ago I switched it back on since it was about 85 degrees upstairs and the kids were sweating in their sleep. I went outside and noticed the humming of the condenser unit with no fan running. This time I didn't power it off right away. Instead I allowed the humming to continue with the heat radiating from the condenser coils. After a couple minutes, the fan kicked in and started blowing hot air. The A/C has been blowing cold now for about 1/2 an hour and has dropped the temp a couple degrees - it is blowing pretty cold!

Again my question to the experts: Is this normal? Does my system need to reach a certain head pressure before kicking on the condenser fan? Would it be helpful to hook a manifold gauge up to see the high side pressure when the fan isn't running? I'm just worried that I'm making a big stink over nothing, but it has always been my understanding that both the compressor and the fan should kick on at the same time.

I will still be cracking it open tomorrow to inspect the contacts and relay, and to see if the capacitor is bulged; I will also check for continuity in the fan wiring to make sure there is no short to ground. And yes, of course I will switch both sets of breakers off and will disconnect the shutoff; I am also familiar with discharging the cap so I don't vaporize myself. I just hope it's something simple like theh cap or contactor...

Incidentally, if the pressure did get too high, wouldn't a high-pressure cutoff switch kick in to protect the system, along with a possible breaker trip?

I've never seen a home unit that operated the fan based on high side pressure. It's certainly possible, just never run across one. Of course, I only play an a/c repairman on the internet.

Higher end units generally have more protection switching, such as a high side cutoff. But builder grade units don't. The compressor will have a thermal overload, and eventually it would probably kick in.

Even if the fan was triggered by high side pressure, I'd expect it to start running 10 seconds after the compressor started. The pressures ramp up quickly.

There's something else going on, just don't know what.

- JimY

a newer unit MAY start the compressor first
and after a delay start the fan

that would avoid both starting at the same time
as A/C motors suck up juice to start
and need far less to run
and the coils need to heat up
before they need a fan blowing on them

in the quest for ever lower power use
some makers are try tricks like that

I would agree it's certainly possible. Not all units are built alike.

An internet search on the make and model number would probably provide specifications on the unit.

Danny