Go Back  DoItYourself.com Community Forums > Heating, Cooling, Air Conditioning, Ventilation and T-Stat Controls > Air Conditioning and Cooling Systems
Reload this Page >

Contactor or temp sensor issue; contactor works in day, not at night (cooling)

Contactor or temp sensor issue; contactor works in day, not at night (cooling)


  #1  
Old 08-26-12, 03:42 PM
H
Member
Thread Starter
Join Date: Aug 2012
Posts: 4
Upvotes: 0
Received 0 Upvotes on 0 Posts
Exclamation Contactor or temp sensor issue; contactor works in day, not at night (cooling)

We have an older RUUD 10 SEER heat pump and it's been working fine until last week.

The inside unit model is UBHA-17J15MUAAI.
The outside unit model is UPKA-036JAZ.

The thermostat is a Honeywell PRO TH3000 Series. It's a digital non-programmable thermostat. It is not the original one we started with, which was manual, but our heat pump company installed the new one for us a couple years ago and it has not given us any problems.

There is nothing flashing on the display or any sort of error codes. It looks normal when this problem happens.


It's summer time; we've set the thermostat for COOL @ 77 F.


I noticed one night last week, at 11 pm, that cold air was not coming from the vents. T-stat was still set for 77 but the inside temp had climbed to 79. The inside unit (air handler) was running fine. The outside unit (fan/compressor) was not running. Instead, I could hear a click, click, clicking sound in the outdoor unit.

I removed the service panel and I could see that the contactor was making the noise. It wouldn't pull closed, but it would jiggle every time the electricity tried to pull it down into position. I could hold down the contactor by hand, and the compressor & fan would begin working... but I could still feel the clicking as I held it down. Letting go would just allow it to spring back up into the open position.

The outside temperature here lately has been a high of 85 F and a low of 60 F. Our thermostat inside is almost always set for 77-78 F in the summer.

During the daytime, the heat pump works perfect. The air is super cold like it should be, and runs without any noises or issues. It works fine all day long until the outside temperature starts to drop below 70-something. Then the contactor refuses to work. The next morning, it will magically work perfect again.... but this doesn't happen every night. It's a completely random intermittent problem... but when it does fail to close, it is always at night.

When I catch it happening, I set the t-stat to OFF and the fan to ON, so we can at least circulate the air inside and give the outside unit a rest (no clicking during the night).

The house is still hot from the daytime sun, and inside temperature will stay around 79-80 for the rest of the night unless it magically decides to keep working for the rest of the night, in which case it will run as it should without issue.

It's as if our heat pump is trying to tell us to turn off the unit and open some windows to let cool air in at night... it's haunted!


If the contactor wasn't getting enough current or if it were worn out in some way, it shouldn't be working at all, right? Or it would get stuck in the closed position.

All I can think of is maybe there's something wrong with a temperature sensor somewhere in the outside unit... and when it senses the cool night air it decides to quit closing.

Contactor part number is 42-25101-01, and would be a simple and cheap part to replace, but if it works perfect in the daytime then it must be something else...

If you have any suggestions for me, I'd be glad to hear it! I do not have a multimeter for testing but I can get one to use.

I'm also having a lot of trouble finding information on how to troubleshoot (or where to locate) the outside ambient temperature sensor. All I can find is some obscure references for the defrost timer (T1/T2/T3 = 30/60/90 minutes) but that is for winter time use when the heat is selected. Just for kicks, I've tried putting it on either of those 3 settings just to be sure it wasn't that.

I can't think of anything else at the moment that can help with a diagnosis via the internet. Feel free to ask anything and I'll try to answer with as much detail as possible.

Please help!
 
  #2  
Old 08-26-12, 06:53 PM
F
Member
Join Date: Mar 2006
Location: Wet side of Washington state.
Posts: 16,321
Received 39 Upvotes on 31 Posts
I know almost nothing about heat pump control circuits but I'll give it a shot. I don't think that the problem is with the defrost timer or any outside temperature sensor. Even in defrost cycle the heat pumps I am familiar with run the compressor, they just cycle the reversing valve.

Normally if a contactor coil was going to be intermittent it would be much more likely to fail during the hotter periods rather than at night so this is a definite stumper for me. It could be a case of low voltage at the contactor coil but you need to have the meter to measure that. I think the voltage would have to be really low, probably less than about 16 volts before the contactor would drop out from a normally energized position.

It just might be a low suction pressure issue along with leaking suction valves on the compressor itself along with a low refrigerant level but I'm really pulling that from left field. Also, this would only apply if the unit had a low suction pressure safety switch in the control circuit.
 
  #3  
Old 08-27-12, 09:53 AM
H
Member
Thread Starter
Join Date: Aug 2012
Posts: 4
Upvotes: 0
Received 0 Upvotes on 0 Posts
Yep it's certainly a stumper. it's definitely an ambient temperature related issue. Letting the unit simply rest for several hours, or all night, doesn't help at all... it waits until the ambient outside temperature has warmed up before deciding to work. I just haven't pinpointed the exact temperature at which the unit fails to close the contactor.

But like I said, if it were to be low voltage, then there's no reason for it to work flawlessly when it's warm outside and then fail to close when the sun starts going down.... the difference between 80 and 70 degrees should be negligible to it.

But maybe, just maybe, it is getting low voltage but just enough to work when it's warmed up by the sun... and that slight temperature difference outside at night is enough to make the contactor to not want to stick closed?

Then again, when it's failing to close, and I hold down the contactor, it keeps getting the same jolt of electricity every second, click click click, and I can feel it every time it kicks.

We've reluctantly called the so-called "professionals" to come take a look at it, so they might stop by later today... I just don't know what time of day they'll come, they might not find what's wrong with it during the daytime.

In the meantime I'm still welcoming any info or advice!
 
  #4  
Old 08-27-12, 03:44 PM
hvactechfw's Avatar
Member
Join Date: Jan 2011
Posts: 5,491
Upvotes: 0
Received 4 Upvotes on 4 Posts
you will need to trace the low voltage circuit from the air handler to the HP and find if and where there is a thermostat that is keeping the the contactor from receiving power to close the contacts.
 
  #5  
Old 08-30-12, 12:58 PM
H
Member
Thread Starter
Join Date: Aug 2012
Posts: 4
Upvotes: 0
Received 0 Upvotes on 0 Posts
The contactor was replaced, but it was still behaving the same way, not working at night when it's cooler outside.

The compressor time delay relay has now been replaced too, so I'm waiting to see how that works out.

I don't know enough about this stuff to test things with my own voltage meter, and we can't get anyone to come out to check on it in the middle of the night when the problem presents itself...

I'll come back to update this thread once the culprit is definitively tracked down.
 
  #6  
Old 08-30-12, 02:34 PM
R
Member
Join Date: Apr 2011
Location: nj
Posts: 526
Upvotes: 0
Received 0 Upvotes on 0 Posts
Is there an outdoor cutoff that will keep the unit off if its cooler outside??
 
  #7  
Old 09-09-12, 01:05 PM
H
Member
Thread Starter
Join Date: Aug 2012
Posts: 4
Upvotes: 0
Received 0 Upvotes on 0 Posts
It turns out that it was a bad time delay relay, which is the little black box that wires come from before they get to the contactor. It was a simple $25 part. The old contactor was still working fine, but it was also very worn and corroded so we kept the new contactor too since it was only $20. As long as the compressor keeps working, our unit should be good for several more years of use now. Thanks for the replies/help!
 
 

Thread Tools
Search this Thread
 
Ask a Question
Question Title:
Description:
Your question will be posted in: