A/C line frozen,outside unit won't shut off

[jonmiles]

Hello again:
(Lazypup) You remember our last problem with the outside unit was about 2 wks ago. The A/C has been working fine for the past 2 weeks. We leave it set at 78 cool and the outside temps have been about 85 so it has been running on and off during the day.

I wake up today and notice the outside unit is running but the inside fan is not ? I check the thermostat and it is set to 80 which I did last night before going to bed and the inside temp shows 77, (because it is colder outside overnight). I'm thinking the contactor relay must be stuck closed from when it was running during the day and the outside unit has been running for who knows how long. maybe 24 hrs. I walk outside to look at the unit and see the lines are very frozen from the compressor to the inside coils. So I shut the unit off from the breaker box. I remove the service panel on the A/C unit and remove the contactor relay cover and find the main power wire for the contactor is burned and the contractor has gotten so hot it's contact points are burned. The main power wire got so hot it melted the casing on it and the wires from the super boost melted into the main wire. Lucky for me the casing on the super boost wire didn't melt and allow wire to wire contact but I'm sure it wouldn't have been much longer before that happened if I hadn't shut the unit down. I took pictures to show the current condition of the brand new ( 2 week old) contractor relay and the main power wire attached to it.

Can someone please tell me if the contactor relay stuck in the closed position and caused such a load on the contact points and wires that they melted ? And what would have caused the contactor relay to stick closed when it has a cover over it to prevent anything from interferring with it's operation.

Next question. Why didn't the defrost sensor switch the unit into defrost mode to prevent it from freezing ?

Is this a common problem with the contactor relay sticking ?

I was told before to never run the outside unit without the inside fan running because it would cause the unit to freeze up. It sure did freeze up, BIG TIME!

Any ideas ? Thanks for your help in advance. : )


PICTURES (DIRECT LINKS)

http://img100.exs.cx/img100/3909/outsideunitfrozenlinepic.jpg

http://img100.exs.cx/img100/7830/Mainpowercontactorwireburned.jpg

http://img100.exs.cx/img100/5614/Contactorrelaywithburnedwire.jpg

[LazyPup]

The ice was caused because the condensing unit continued to run after the inside unit fan shut down. First the inside coil ices, then the suction line right on back to the condensing unit.

The defrost sensor only senses ice on the outside condensing unit coil when a heat pump is set on heat mode.

It appears as if the condensing unit contactor overheated and stuck in the closed position. I would suspect that you possibly had the wrong contactor.

You will have to begin by changing the contactor. NOTE: Check the manufacturers data plate on the condensing unit. Heat pumps and larger AC often use 40 or even 50 amp rated contactors, while most AC units use a 30amp contactor. It is very easy to get the wrong contactor as they all look the same. You must check the label to insure you have the right one. Contactors must be rated equal to or greater than the demand load of the unit.

The problem can also arise from a loose wire terminal. Even a slightly loose wire connection will result in an excessive amp draw. Check all wire terminals and connections on the compressor, capacitor and fan circuits. If you see any evidence of a burnt or corroded wire end, cut the bad part off and get back to clean wire.

If it is necessary to replace any wires make sure the replacement wire is the same guage and has an insulation rating to match the original wire.

Check both the fan and hermetic sides of the motor capacitor. A faulty capacitor will result in a very high amp draw.

Thoroughly check the outside fan motor. If the condenser fan motor stops the refrigerant head pressure will go excessively high and result in a high amp draw on the compressor. In addition, if the fan motor stopped as a result of a bearing seizing up, the fan motor will be in a locked rotor condition and the motor amp draw will be excessively high.

Once you have the contactor replaced and can get the unit running it would be best to use a snap on amp meter to check total amp draw to the condening unit. If the total amp draw is higher than the rating you should then check compressor amp draw and motor amp draw to determine what is causing the excessive load.

NOTE: kirchoffs law states that the amount of amperage leaving a circuit is equal to all applied amperages. Since motors have amperage applied on both the start and run windings you must take the amp reading on the motor common wire to get the total amp draw.

Most homeowners or DIY'ers are not familiar with snap on ampmeters as they are a fairly expensive piece of test equipment, ranging from about $75 to $150. Although that may seem a bit much for homeowners occassional use they are a very rugged (I have been using my Sperry SPR 300 since 1985), easy to use piece of equipment that is almost indespensible to electricians, HVAC/ Refrigeration techs, motor techs or appliance servicemen.

Most of the snap on amp meters combine all the features of the common VOM (Volt/Ohm/Milliameter) as well as having the ability to measure amp loads up to 300 amps or more.

To take an amp reading you first select the appropriate scale for the anticipated amperage, then depress the side button and the jaws open. Snap the jaws over the wire in question and you instantly get the reading. I have added a photo of a snap on ampmeter checking a wire in a breaker box.

[jonmiles]

Lazypup, Wow! great reply. Thanks

The contactor relay I replaced was not bad but was showing wear after many years so I thought why not replace it while I was at it. The new one was EXACTLY the same rated because I took the old one with me and matched them exactly. And remember the unit had been running on the old one for years with no problems.

The capacitor was just checked out 2 weeks ago and I added a super boost to the unit for extra help because the parts guy told me I should have one for a heat pump and it shows one as optional in the wiring shcematic. I installed a brand new fan motor 2 weeks ago too and it was still working fine when I turned the breaker off to kill the outside unit.

What does make sense is a loose wire. Notice in the picture of the contactor relay that only one side of the relay is burned/colored ?

The wire which is burned in the picture came off of that same side and when I touched the wire it came loose from the screw which would indicate it was very loose.

So it sounds like the problem was caused by a loose main wire connected to the contactor relay and everything else followed after the contactor stuck.

Would you replace the contactor relay or just connect the wire better this time and run it to see what happens ?

picture of original contactor relay

http://img85.exs.cx/img85/7038/originalcontactorrelaysinceweboughthouse.jpg

thanks again
Jon

[LazyPup]

That is a cuttler-hamer contactor which is a very highly respected manufacturer of quality materials. If it was working ok there should be no problem with using it again.

Examine the electrical contacts where the moving armature opens and closes. If they are not burnt or pitted you should have no problem.

i would suggest you get a product called "Nolox" which is an antioxidant to put on the wire ends and in the contactor main wire terminals before you reccnnect it.

Nolox is sort of a thick gray paste that comes in a plastic squeeze bottle and is made to put on electrical contacts to prevent corrosion and it helps dissipate heat. (Do not put it on the contacts where the moving armature meets the contactor fixed contacts).

It is also a good idea to put a bit of Nolox in wirenuts before making up joints that are outdoors or exposed to humidity or extremes of temperature.

You may be able to find it at the big home supply stores, if not, you can get it at any commercial electrical supply house.

[jonmiles]

Thanks Lazypup

So you wouldn't use the one that is on the unit now. The one I installed 2 weeks ago. There is a picture URL of it on the original post showing the relay. The old cuttler-hamer contactor had pits on the shunts/contacts which is why I replaced it.

[jonmiles]

I found the problem.

The contactor relay was broken. The screw where you connect the 240 main power wires cracked the plastic inside where another little phillips screw held the contact plate in place this vibrated out and then the main screw and plate was able to move causing the heat build up. I have to say the new contactor relay I installed the first time 2 weeks ago was a very poorly made part. After wrenching on cars and motorcycles I know not to over tighten anything with plastic : ) and was very careful not to tighten more than needed to keep the wire in place. But when the wire continued to move back and forth I continued to tighten very slowly until I heard the crack of plastic but at that time didn't find anything loose and the wire was tight so I pulled on it a little to make double sure and figured it must not have been a problem (wishful thinking). Needless to say it was and I found out the hard way when my wire came loose.

I now have a new contactor relay which is a much better part starting with metal blocks for the screws with copper terminals and FLA 40 rather than FLA 30 and RES 50 rather than RES 40.In other words it is a much higher end relay then the first one I purchased. And it cost almost twice as much too. I installed it with no problem and no cracking plastic : ). If I would have known what a poorly made part I was purchasing the first time I would have bought the more expensive one. And because I bought it at a wholesale warehouse and I'm not a HVAC TECH they wouldn't warranty it. Which made things harder to accept when buying poorly made parts. Oh well, it was still cheaper than that service call. And I learned a little bit more........

Thanks Again.

Jon

[LazyPup]

John,,

For the record, the relay pictured in your last post has a severely burnt contact on the right side, that is why I suggested considering the original, but since as you say, it also had pits on the contacts you definitely did the right thing by getting a new one.

We are certainly glad to hear that you now have everything under control, and based upon what you stated it appears you have done an excellant job of troubleshooting.

If its any consolation most parts houses have a no return policy on electrical parts. That rule applies to trained service techs as well as over the counter cash sales. Ask any tech and they will tell you war stories of how many repeat service calls we made learning that lesson.

[jonmiles]

The parts guy told me he has cracked many himself before learning to just tighten enough to hold the wire. I replied, if the part had metal blocks for the screws this wouldn't be a problem. He said, I know but nobody wants to pay the extra money and after you learn not to tighten the screws on the cheap ones they will work and you can make more money on the service call. It's all about saving a dollar.

He didn't sell me the first one, it was another place. The guy who sold me the higher end part is who helped me with the trouble shooting as well.

All is well again : ) Thanks for everything