Thermostat Adjustment

[Mike Jean Bandfield]

We did a 3 week winter trip and found that when we set the thermostat on 69 the furnace would come on at 63 and shut off at 75. Sound familiar?

The thermostat has an adjustment call the "anticipator" that controls the duration of burn cycles. From the factory, ours was set at the lowest setting. A look at the manual does not provide any direction as to where it should be set. There's a direction to put it at the same setting as the unit you are replacing. That's not much help because we replaced the whole RV not just the thermostat.

As a starting point I set the anticipator at mid range and found it to be quite satisfactory. The unit does not cycle too frequently and the temperature stays within comfortable swings. The trade-of is the extra use of battery power which I haven't quantified and possible harm to the furnace over time if you set the cycle too short however, then manual doesn't state what is considered too short.

To adjust, remove the cover on your thermostat and you should see an adjustment similar to the one I've pictured below. I set mine for .27 - YMMV.

Mike

[Trisha]

Wow, What a difference. I always wondered why it had to oscillate (temp wise) so badly. It really doesn't cylce a whole lot more often but it doesn't overheat me so much now and it doesn't get so cold. I am SO glad you posted that!!! Thank you thank you thank you!

Trish

[bcope01]

I set mine for .27 - YMMV.

Mike and Patricia:

Now that you've both completed a winter season with your Suburban furnace thermostat anticipators set at .27, I was wondering if you've experienced any problems with the lower setting.

I ask because the Suburban Technical Manual (an excellent document on the installation, operation, cleaning and maintenance, trouble shooting, and parts specifications), states that for funances manufactured from 1985 forward, the anticipator should be set at .7 based on the amp draw (.5 for furnances made before 1985). See pages 4 and 9 of the manual for a detailed discussion on the Suburban thermostat and how they arrived at a .7 anticipator setting. The manual can be found at:

http://pweb.amerion.com/~scopedude/pdfs ... Manual.pdf

I'm not sure how critical the setting is, but wouldn't want anyone to experience an early furnance failure due to an incorrect anticipator setting.

Bill

[Mike Jean Bandfield]

Bill, thanks for the manual. It is much appreciated. I searched high and low for more info without results. And the data sheet supplied by the factory was inadequate.

We spent about a month on the road this past winter with no problems and were much more comfortable than the factory setting of 1.

Next winter I'll try .7. If it goes back to a 12 degree swing I'll do some more testing but just might split the difference and live with the risk.

Mike

[Trisha]

I did not set my quite to .27. Unfortunately, I don't have the rig here to go look. I hate having to say that. What a pain...

However, it was close to that and i was quite comfortable.

For the sake of discussion, why would they allow a setting that would destroy the device? Or even considerably shorten it's life? If having tthe thermostate be adjustable is harmful, then why do it? Since it is adjustable and flexible, I am assuming that it is not deliterious to the equipment. I should be able to assume that manufacturers won't allow you to set things to self-destruct without at least a warning, and I didn't see one.

Yeah, I took it to philisophical. Practically, I found Mike's advice to be most helpful as I was freezing my buns off before it kicked on, and then it had me sweating before it turned off. Can't imagine that would be good for MY eventual health....

I did find that it's easier to keep up on heating if you use the heat strip (if you have one) that comes on the rooftop air unit. Matter of fact, it was more stable at keeping me right at 70 than the furnace, which I only used if it got into the 20s. Unless I didn't have shore power.

I've never had the furnace drain the batteries overnight, btw, even with heavy use. But if I'm boondocking like that, I either have to run the generator for other reasons anyway, or I'm on the road and the alternator has the batteries recharged to peak before the next night.

Maybe once the batteries are more seriously old.?

Please tell me, though, if you know instances of manufacturers that make things easily adjustable into ranges that will self destruct the item, without at least pointing out the danger?

Thanks,
Pat-trish

[bcope01]

I did a little more research online and was able to identify one potentially serious downside to setting the anticipator at too low a setting:

Lower setting values for shorter cycles, higher for longer cycles. Older standard furnaces this is usually 0.2 to 0.4 amps. Mid-efficiency and high-efficiency are longer 0.8 to 1.2. The burner should run for at least 2 -3 the minutes before turning off. Short cycles will result in flue gas condensation. The condensed flue gas is very acidic and can prematurely rust out the furnace, vent connector and chimney. As little as one season can rot out a heat exchanger.

The complete discussion can be found at:
http://www.hvacoracle.com/cgi-bin/publi ... &s=heating

Bill

[Mike Jean Bandfield]

The complete discussion can be found at:
http://www.hvacoracle.com/cgi-bin/publi ... &s=heating

That's a good technical explanation of the anticipator operation. I've saved it to my technical file. It's nice to understand the potential consequences of fooling around with the setting.

It would appear that the factory setting of 1.4 is the "lowest risk & highest efficiency" setting. However, this comes at the price of also being the "least comfortable" setting.

By the way, the cycling at the lower setting doesn't seem too extreme. The furnace comes on and stays on for at least 5+ minutes depending on how cold it is outside. I doubt that anyone having the same furnace as ours would have damaged anything. So I'm not too concerned about it. Even so we will move it to the recomended seting of .7 and see how it works next fall.

Mike

[Trisha]

That is interesting. A little better understanding now.

I do believe the cycles worked at Mike said though, at least 5 minutes though Inever timed them. I will this fall.

Patricia