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Auto isn't working on my system

3K views 30 replies 10 participants last post by  Chimmy 
#1 ·
Hi all,

I am having an issue with my system, and I am hoping that someone can give me a little insight.

If I have "auto" enabled the system just wont fire up. I have to manually switch to "on", and then set the panel to either "heat" or "cool".

I have installed a new thermostat so that doesn't seem to be the issue. I was wondering if there is another switch at the boiler end of things.

This is an OLD system. Here is a pic of what I considered might be the source of the problem. (shouldn't this be better enclosed???)

And advice would really be appreciated. :)

Hugh

 
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#17 ·
He said it was the limit & thermostat. Previously, he had given the $600 - $700 estimate to my wife. I'm going to have a guess that changing that part out shouldn't be anything as costly as that. I know that in an ideal world, I would replace everything. But right now, 4k .......

Thanks for the reply, I appreciate it. :)

Hugh
 
#2 ·
Does your stat use the same button to select 'auto', 'heat', or 'cool'? If so, the 'auto' refers to automatically switching between heating and cooling, not the fan. In this case, there would be another switch to control the fan.

On my stat, the auto position will not 'fire' up the heat unless there is (at least) a 10 degree difference between the 'heat' and 'cool' setpoints. This could be your problem.

If so, just put the stat on heat when you think you will need it.

V
 
#3 ·
Hi,

thanks for the reply. No, it's different buttons.

The FAN button gives me the option of AUTO/ON
The SYSTEM button gives me the options of OFF/HEAT/COOL

So it I have the FAN set to ON then of course it runs constantly. If I set it to AUTO, it doesn't kick in.

Hugh
 
#4 ·
What the auto position does is allows the fan to come on when the thermostat calls for heat or cool. In heating mode there is often a short delay before this happens....in cooling mode it often happens immediately.
Are you saying that when the unit is calling for heat the burners come on but the fan doesn't? I'm not exactly sure what issue you are having.
 
#7 ·
Thanks for the replies guys. I'll have to check in the morning (late here now) but I think that the burners come on, but not the fan. I'll double check that though.

I actually thought it was an issue with the thermostat, and I replaced it. But still the problem exists. So, if I set the timer, when the trigger time rolls around, nothing happens.

Right now, if I want heat I have to with to HEAT, and turn the fan to ON.

I really appreciate the replies, I'll have another look tomorrow and post my findings.

Thanks!!!!
 
#8 ·
There a few different types of controls that turn on the fan in a heating system. One is a fan / limit switch. It turns the fan on upon heat rise. There are types which do not rely on heat, they are timed. A model number and some pictures wouldn't hurt. I suspect that furnace is not that new. Any chance there is a schematic somewhere...perhaps on one of the removable panels?:whistling2:
 
#13 ·
If anyone has any ideas on this I would really appreciate it. Leaving the country in a few days for two weeks, and I'd like to resolve this so the wife and children are all set with auto heat.

Thanks!!!

It's time to call in a HVAC pro. You want your family safe and you don't want to have to worry while you are gone. It's cheap insurance to have it fixed correctly now, rather than wait.:yes:
 
#12 · (Edited)
call a service company if you really care about the family as it sounds like the fan limit is broken .I know this is a DIY site but sometimes we need to know when we are in over our head and call a pro. it is NOT a fix but in the thermostat set up you can set it to bring on the fan with a call for heat repeat not a fix
 
#15 · (Edited)
Ok, so you guys are stars - I think your assumptions were spot on! :)

And so, I decided to call in a pro - but I think that this has led to a little disappointment:)

As I am leaving to pick up my kids from school, a guy arrives. Fifteen minutes later my wife is calling me to say that we are pretty much in mortal danger if we run the system!

Now, it is an old system, no doubt. But it runs - and the motor was changed a year ago. We have the house smoke alarms fitted with carbon monoxide detection, so that isn't worrying me.

I asked how much it would be to just fix the current issue - $600 - $700!!! Really???!!!! I honestly cannot see how that amount of money could be spent to replace a faulty switch. Am I missing something?

Anyway, the guy was still there when I got back, and when pressed gestured to the general direction of the issue (the pic below) But he was clearly looking to have me spend 4k on a new system.

I am thinking it's the item on the left that's the problem. Anyone have any input?

So that's my story - I definitely felt that I was being led somewhat.

Hugh

EDIT - he also said my thermostat was faulty - not sure how he arrived at that, but it's only 6 months old. I know it could still be a dud, but odds are against it. Turns out, his new system comes with a thermostat! Awesome, huh?


 
#20 ·
The device on the left is the limit that prevents the burner from running. The device on the left is what runs the fan during a heat call when the thermostat is in the fan "auto" mode.
 
#21 ·
I didn't do anything. Prices were left for a total replacement.



Beenthere - you said they are both on the left. :) Can you clarify which is which. (bearing in mind my system just isn't working on auto) May I also ask, any reason why I shouldn't just source the part and fit it myself?

Thanks!!!!

Hugh
 
#24 ·
So, I decided that before changing parts myself I would get a second opinion.

Guy came out, agreed that the fan limit was not working. He cut a section out if the casing and checked the heat exchanger - and reported that he was surprised that a unit fitted when the house was built, 1972, had no cracks.

He also checked for the dangerous levels of carbon monoxide the previous guy reported, insisting that the system should NOT be switched back on - and found absolutely none!!!!

So, new switch fitted, everything working just fine - $310.

Thank you all for your help. :)
 
#25 ·
The part on the left is high temp limit,on the right is fan control.Fan control has been replaced,with a more modern fan/limit control but only fan control side is being used.To me it sounds like the fan center that is on the outside of furnace isn't wired properly.Power should be coming out of fan control,then into normally closed contacts in fan center then to the fan motor.Sounds like this is where you might be wired wrong.Fan center is added when ac was installed.
 
#31 ·
Fan relay has a NC and NO switch, low speed is the

heat speed and is run through the fan relays NC switch and is controlled by the temp delay.
When the fan relay is energized the NC opens and NO closes bringing on high speed. The fan relay is only energized in fan or cool modes, the temp delay controls heat/low speed fan
 
#30 ·
The time delay controls low/heat speed

<a href="http://tinypic.com?ref=2h4er7l" target="_blank"><img src="http://i45.tinypic.com/2h4er7l.jpg" border="0" alt="Image and video hosting by TinyPic"></a>


While the fan relay runs high or cool speed
If in heat mode the temp delay is bad, if you have a time delay or time/temp delay same goes for therm.
 

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