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#529376 - 07/14/05 11:56 PM Lubricating A/C Condenser Fan Motors
TxGreaseMonkey Offline


Registered: 07/14/05
Posts: 313
Loc: Texas
Life in Texas without air conditioning would be unbearable. I recommend yearly lubricating your condenser fan motor's sleeve bearings with an ISO 32 turbine oil. Top lubricants would be Amsoil's RCH Series, Synthetic RC Series Rust & Oxidation/Antiwear Gear, Bearing, and Hydraulic Oil, or Exxon Mobil's SHC624 Synthetic Motor Lubricant. Unocal 76 also makes a fine ISO 32 mineral turbine oil, available from ACE Hardware, in a 4 oz. zoom spout oiler. 15 drops of oil, per bearing, is all you need. Make sure to turn off the 220v. breaker to the air conditioner and the 110v. breaker to the furnace, before ever servicing the unit.

If you regularly hose off your condenser coils from the inside, lubricate the condenser fan motor, and replace the contactor every 6 to 8 years, you will greatly extend the life of your unit, save yourself a lot of money, and not have it die on the hottest day of the year.

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#529377 - 07/15/05 12:12 AM Re: Lubricating A/C Condenser Fan Motors
JohnnyLock Offline


Registered: 05/23/05
Posts: 51
Loc: Houston, Texas
My monster-in-law found that out the hard way this year -- in Houston -- got to about 90 F inside her house after the ac quit -- was the condensor fan motor. That is good info to know. She took it hard in the pocketbook to get it fixed (July 4th weekend).

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#529378 - 07/15/05 12:29 AM Re: Lubricating A/C Condenser Fan Motors
TxGreaseMonkey Offline


Registered: 07/14/05
Posts: 313
Loc: Texas
Condenser fan motors are thermally protected and shut down, when the bearings overheat. When that happens, it's best to replace the motor with one that comes with ball bearings.

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#529379 - 07/16/05 06:26 PM Re: Lubricating A/C Condenser Fan Motors
Kestas Offline



Registered: 06/04/02
Posts: 10774
Loc: The Motor City
What is the contactor and how difficult is it to replace?

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#529380 - 07/17/05 12:59 AM Re: Lubricating A/C Condenser Fan Motors
kenw Offline


Registered: 10/10/04
Posts: 1979
Loc: Houston
the contactor is the relay. it is usually located inside the outside (condensor) unit. I designed and built commercial AC units for a few years and I never heard of replacing the contactor unless it was broken. However I have seen several service providers recommend some rather dubious "preventive maintenance" procedures.

Undersized ones can develop pitted contacts and eventually weld themselves closed, but a properly designed one will outlast the rest of the unit.

Actually a common failure for the contactor/realy is ants....for some reason the ants are attracted to the relays and build nests all over them. It's weird but I've seen literally dozens with ant infestations. One smushed ant in the contacts means no AC...

Rather than replacing the contactor (they aren't cheap), I would apply a decent ant killer every year...

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#529381 - 07/17/05 01:05 AM Re: Lubricating A/C Condenser Fan Motors
TxGreaseMonkey Offline


Registered: 07/14/05
Posts: 313
Loc: Texas
The contactor is the main relay in your outside air conditioning unit. It's responds to your indoor thermostat, by opening and closing contact points. They are similar to the points in distributors years ago. When the points close, power flows to the compressor and to the condenser fan motor. Unfortunately, they pit, over time, as they open and close (due to arcing). As the cross-sectional area of the points is cut in half, the resistance goes up four fold (a square function). Remember the area of a circle = pi x r-squared. Replacing this relay is the key to maintaining your AC. As the risistance in the circuit goes up, your compressor gets starved for current (amperage) and it burns up. Fire ants and spiders also are attracted to the relay and become a dielectric.

Normally, 12 wires or so go to a contactor, so you have to take your time. It took me 25 minutes the first time I ever replaced one. An HVAC technician might charge you $80 - $150 for the contactor and $150 to replace it. I bought my first one for $15 and then found a place that sold me one for $9. Part of the challenge is finding a place that will deal with you. Traditionally, HVAC technicians have had this market unto themselves. Cracks are appearing, due to the internet.

[ July 17, 2005, 04:31 PM: Message edited by: TxGreaseMonkey ]

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#529382 - 07/17/05 06:42 AM Re: Lubricating A/C Condenser Fan Motors
kenw Offline


Registered: 10/10/04
Posts: 1979
Loc: Houston
Again, only an improperly sized contactor will fail in the manner you describe. The current will remove any corrosion unless the current density is too high for the surface area of the contacts, ie, the contactor was undersized. It is important that any replacement contactor be rated at the same or higher in current capacity, and of the proper voltage rating.

Typically the contactor handles 240VAC on these power contacts, buying one rated for 120VAC will work for awhile but will fail prematurely.

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#529383 - 07/17/05 09:03 AM Re: Lubricating A/C Condenser Fan Motors
TxGreaseMonkey Offline


Registered: 07/14/05
Posts: 313
Loc: Texas
kenw, most air conditioner contactors will eventually die in the manner I described, unless fire ants ruin them first. It has nothing to do with corrosion or installing an improperly sized contactor (who's stupid enough to do that, when we are talking about 240 VAC). Plain and simple, it has to do with the destruction of the contacts due to arcing; i.e., they literally erode to the point where very little is left or they weld shut. Yes, kenw, this is how most contactors "break." A few contactors bite the dust due to the 24v. coil failing. You should go back and examine the contacts on some of the commercial AC units you designed in 6 to 10 years. You will get quite an education. Experience, from working in a field for a long time, is always the best teacher. Even though I went to engineering school, experience allows me to know what I'm talking about.

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#529384 - 07/17/05 10:07 AM Re: Lubricating A/C Condenser Fan Motors
TxGreaseMonkey Offline


Registered: 07/14/05
Posts: 313
Loc: Texas
An indication that your contactor needs replacing is when the thermostat is set to air conditioning, the furnace blower is running, cold air is not coming out of the vents, and the outside air conditioner is not running. Contactor points frequently wear unevenly and at an angle. When this happens, they begin to "hang up," by not closing properly, and your compressor and condenser fan won't run. You will be amazed how much better your unit runs when the contactor is replaced. The compressor gets up to speed faster, since it is no longer being starved for current. Immediately you, and your wife, will hear and tell the difference, just like when you replaced worn, pitted points in older cars.

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#529385 - 07/18/05 03:51 AM Re: Lubricating A/C Condenser Fan Motors
kenw Offline


Registered: 10/10/04
Posts: 1979
Loc: Houston
I am a mechanical engineer, I designed not only AC, resolved escalated service calls from the field, handled all regulatory information and was responsible for all connectors for a large electronics mfg ($40B in rev).

i give up.

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