Solenoid valve?


  #1  
Old 08-30-08, 02:44 PM
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Question Solenoid valve?

I have a Whirlpool central A/C unit of some antiquity (I can't find anything on the Web that refers to or even resembles it). The unit stopped working, and I eventually traced the problem to a blown 3A fuse on the furnace control board (York Diamond 80).

The problem may have originated when something stripped about 8" of the outside control wires bare, and they shorted. After replacing the wire and fuse, I found that reapplying power would simply blow the fuse again. I had a tech look at it, and other than disconnect most of the internal and outside control wires before walking off the job, he did nothing (long story); however we did replace the control board and now the fuse held.

When (after some research) I reconnected everything, the furnace and fan are working correctly, as are the outside unit's contactor, compressor and fan. But if I connect the wires from what appears to be a liquid line solenoid valve to the thermostat control lines, it promptly blows the control board fuse again. I don't know that these lines were connected before, but I assume they were. I can find no wiring diagram for the unit (it came with the house), but it appears that the solenoid wires are supposed to connect to the contactor along with the thermostat control wires.

When I measure resistance across the solenoid, I get zero. Not low resistance, but zero. So I assume the coil is shorted, and I was shorting the thermostat control lines when connecting them to the solenoid, thus blowing the control board fuse.

I left the solenoid valve unconnected for now, and have A/C in the house when requested by the thermostat. Which is quite surprising--I thought the value should be normally closed? But the A/C in here seems as cool as ever, which I don't understand. Any ideas?

I also have two other questions:

Am I damaging my unit by running without this valve? I assume it's running at lower efficiency than it should, and maybe all the refrigerant's collecting in the condenser at the valve. How harmful is this?

How do I go about replacing the solenoid valve? Can I remove it without the line spewing coolant? And are these solenoids relatively generic, if I match the physical dimensions and control voltage?

Ok, a third question: Am I totally off the wall on thinking the solenoid is the problem?

Thanks for any and all help!
 

Last edited by homeklutz; 08-30-08 at 04:15 PM.
  #2  
Old 08-30-08, 05:41 PM
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Since most of the super techs are not on tonight, I will try to help.
Sounds to me that since this is an AC only unit and you have found what you think to be a solenoid in a hot line, that you are probably looking at the high press switch. If you try to read the resistance, and it is the switch then it should read zero ohms. It is meant to be connected in series with the control circuit to shut the unit down in case of a press beyound its setting.
What I don't understand is why the wires were just hanging from it when it should be in the circuit. If I am right, it will blow your control volt fuse if you apply control voltage.
Hope this helps. Unless you have more info to offer, I will sign off here and you will have to wait until one of the regular techies are back on line.
 
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Old 08-30-08, 06:02 PM
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Thanks gardener321,
You may be right--I didn't see an external coil. From a horizontal liquid line, there is another line running vertical (up) for about 12", capped with something that has 2 yellow wires coming out. Would this be typical for a pressure switch?

The tech that walked off the job left it with wires dangling, I'm just trying to put them back with the most educated guesswork I can muster. The wire ends look to me to have been attached before. The other dangling wires were the t-stat controls, and two wires attached to the contactor where the t-stat control wires should go. So my best guess was that the yellow leads should be wire-nutted together with the t-stat control to the contactor.

I have been running without it for several hours now and no breakers or fuses have gone yet.

If I understand you correctly, running without it should do no harm in itself, though I risk problems if pressure gets out of control. Is that correct? Tomorrow (as it's dark here now) I'll put it in series as you suggest.

I knew exactly zilch about this stuff before the A/C quit and can use all the help I can get. Thank you very much!
 
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Old 08-30-08, 07:04 PM
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By tomorrow evening, the techies should be back on line. Most all of these guys are full time active service people or contractors. They have access to info galore if you give them the model and serial number of your unit they can tell you exactly at the correct place to rewire the switch. In the meantime however I would find the hot control wire (24vac)and cut it then install your hp switch in series with that wire for protection until you get the correct point of installation.
 
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Old 08-30-08, 07:17 PM
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I'm not a "techie" and my experience is with commercial and industrial sized equipment, not residential.

What you may have is a "pump down" system if you really do have a solenoid valve in the liquid line. This would cause the compressor to continue to run after the inside thermostat stopped the cooling by closing the solenoid valve and the compressor would then pump the refrigerant from the evaporator back to the condensing unit.

Some pictures of the supposed solenoid valve and the supposed pressure switch might help. Pictures need to be posted to a photo hosting site and the URLs posted here. Clear pictures, both close ups and from a distance that shows how it all fits together are best. More pictures are always better than fewer.
 
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Old 08-30-08, 08:44 PM
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Thanks, gardener321 and furd! I'm traveling tomorrow, but by sometime Monday I'll post some pictures of what I'm talking about.
 
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Old 08-31-08, 04:36 AM
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Slight correction.
Don't just wire the switch in any 24v wire, because of a possible branch circuit, you need to make sure that it is series with the one that serves the compressor contactor.
 
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Old 08-31-08, 08:50 AM
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liquid line connections

on a residential AC I doubt its a solenoid,... I too think its either a high pressure safety switch that is normally closed, or it could be a fan cycle switch that cuts the outdoor fan in and out as needed to operate during cool outdoor temps. A solenoid switch would have a coil in conjunction with a low pressure switch. As the thermostat is satisfied the coil would open and block the supply of refrigerant to the evaporator as the compressor continued to run. It would start to drop in pressure and as it hits the LP cutout setting it would open the circuit to the contactor shutting down the outdoor fan and compressor. a photo would help ID the part in question
 
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Old 09-01-08, 10:00 AM
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Ok, I've put the switch(?) in series with the control signal going to the actuator. Everything seems to be working great. I've posted some photos of the unit and the switch(?) to http://www.flickr.com/photos/27692051@N08/?saved=1. I'd appreciate anyone who can confirm what the part is.

Thanks for all the help, you guys have saved me a ton of trouble!
 
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Old 09-01-08, 10:29 AM
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That's the high pressure cut-out....one side of the 24 volt line travels through it. That is why it was open. putting 24 volts into it would be a dead short and trip your fuse at the board.
 
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Old 09-01-08, 10:35 AM
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It sure did. Thanks to everyone for the terrific help!
 
 

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