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Littledj 06-21-2008 04:57 PM

Microwave Fan Turns on Air Conditioning - help please
I have had over 7 heating and air conditioning companies come to my place here in Calgary, Alberta and nobody can help or simply say everything is wired properly. The problem is this: When the thermostat is on "off" and my wife turns on the microwave fan the air conditioner will kick in and drop the house as cold as possible - all this happens with the thermostat in the "off" position and the thermostat fan on "automatic." A guy came on Friday and said this was impossible while I was away on business. I tried it when I came home and reproduced the problem in 30 seconds. I think the problem is that these technicians may not be trained electricians?? This is unreal!! Please help .........and thanks so much!!!!!

geo fan 06-21-2008 05:28 PM

I would not critisize the hvac guys . There is just about no way that could happen that I could imagine with out a manufactured cause . In other words this has either ben a problem from day one or work was receintly done to cause this. That being said the electritian that wired the line voltage is to blame and there is a splice that was thought to power the fan is back feeding to the equip . I would recomend running a new power line from your breaker box to the fan . wire nut and abandon the old wires in junction box . this will most likely be simplier then pulling your hair out tracing out the wires. If the problem persistes call a preist not your hvac guy:thumbup:

Littledj 06-21-2008 05:50 PM

Sears had one of their subtrades wire up the central air 5 years after the house was built. I appreciate your comments!

statman 06-21-2008 10:54 PM

I have got to see this! I own my own HVAC company in Calgary...give me a call 226-6066 and I will try and get over there sometime later this week. Is this fan the exhaust fan for your range as well? Is it a gas range? I suspect that you have a code required air make up system for your house which is designed to ventilate the house when you are cooking. Unfortunately. many people in the trade use the g (fan) terminal to accomplish this but forget that the g will backfeed through the tstat and energize the y (cooling) terminal. Does the ac shut off immediately when you shut off the fan? Also try shutting off your tstat and removing the wire from y on your stat when the exhaust is running...does the ac shut off? If so, then we need to come up with an isolating relay that will prevent ac from coming on when you have the exhaust fan on. Its the only way I can think of to make that work...unfortunately city codes require the make up air system but do not specify on how it should be wired, only that it works.
Hope to hear from ya, Sean
STAT Climate Control

Littledj 06-22-2008 12:15 AM

Yes, the fan is for the range as well. When the microwave/range fan (electric range) is shut off the air conditioner continues to purr, sucking up electricity and turning my house into an icebox. You have shed more light on this in a couple of paragraphs than I have been able to come up with in a year! I really cannot believe my luck. This post was out of pure desperation and I GREATLY appreciate your post. I will call you this week and thanks for taking the time to help somebody out. And yes, we have the code which requires the ventilation.

Littledj 06-22-2008 12:26 AM

Yea Hah!
I Just Turned On The Microwave And The Air Conditioner Started. I Then Pulled Off The Green Y Wire Like You Said And The A/c Immediately Shut Off! Did You Descend Out Of The Sky? When Can I Call You To Finally Put An End To This? 7 Firms And Not One Was Able To Isolate The Problem Like This! Thanks!! One last thing....should I hook the green wire back up until you come out? I look forward to hearing from you.

A couple other wife turned the heat on when she came home because the house was freezing (ventilation fan off well before she left) and the bloody air conditioner remained on when the furnace heat (gas ignited) was on warming the room up. Lastly, one fellow that came said the fellow who installed the air should have put a relay in the furnace and that there wasn't one - but that didn't lead him any closer to providing answers.

biggles 06-22-2008 05:35 AM

if the fan is 115V did you try to power it up from another wall socket. what is the location of the micro fan verses the stat are they opposite each other.try removing the stat off the subbase and running the fan if the micro fan runs your 24V is crossing the power line for the kitchen fan somehow,,the stat wires from the subbase to the furnace need to be RANG OUT especially geting the heat and cooling at the same time.:eek:

8 Ball 06-22-2008 09:22 AM

PLEASE remember that some of us require closure, especialy for something like this!

How about posting what you find STATS! Was a priest and holy water required?:eek:

Littledj 06-22-2008 11:13 AM

The Priest
My wife is Catholic and says she can arrange for a priest if necessary. Her mom keeps saying we need to get the house blessed:thumbup:

statman 06-22-2008 01:29 PM

wow...being compared to angels. Never had that before. Guess I am under the gun to fix need an exorcist when ya see my bill...kidding. Call me and I will let ya know when I can get out there. Where do ya live? Im in Harvest Hills but am usually all over the city. Pretty busy until wednesday then work is just cut back to hectic but I will work ya in. Take care, Sean
You can reconnect the ac wire, but may want to shut it off when you need the exhaust fan. Or just shut off your breaker to the ac when you are using your fan. Not sure exactly how I am gonna fix it but I will fix it will definitely need a relay to isolate your cooling from the mua/ventilation system. The heat issue is the same long as the exhaust runs the ac will run. Anyhow, will see ya later this week.

Littledj 06-22-2008 02:33 PM

Not worried
Not worried at all about the bill. This is Calgary isn't it? There was once a day when you payed a good price to have a good job done. I am old school and you wont have any problems with this fella. I am in Elgin in McKenzie Towne. I will give you a call tomorrow.

8 Ball 06-27-2008 05:31 AM

O.K. its been a week... whats the deal?

statman 06-27-2008 08:24 AM

He was supposed to call me on wednesday....musta got busy but I will let ya know when i do get over there.

statman 07-02-2008 06:52 PM

Still no word...either he is busy or has figured it out. The basic issue is his ac was running when his kitchen exhaust came on. Here in canada u require the furnace fan to come on c/w a fresh air intake fan, damper and thermostat regulated heater when the exhaust is on (over 300 cfm). These exhausts have a separate pressure switch in them which most guys just wire to R and G on your furnace. The problem is that sometimes the 24v signal will backfeed from the furnace up through the thermostat and energize the Y terminal. (Y and G on some tstat subbases are interconnected. So the only real fix is to run the Y wire through a NC contact on a relay that will open Y when the exhaust is running. Hope this helps...will let ya know if I ever hear from him.

8 Ball 07-02-2008 07:37 PM

Thanks for the update. Makes sense and is logical. We dont have that requirement here in Mi., other places possibly. We prevent negative pressure with barometric dampers piped to the mechanical rm..Seems like that would be kinda pricy. Not only adding to your instal price, but operating costs.

Oh well...code is code. Thanks again.

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