At what point can you increase fermentation/condition temp?

I've been reading a lot on fermentation temps in both primary and secondary fermentations. While it is pretty established that primary fermentation temperatures are more critical, there seems to be a lot of conflicting advice on this forum relating to temperatures during secondary fermentation. Some say you need to maintain the low temps used during primary, whereas others say you can let your secondary fermenter get much warmer without any ill effects.

I ask because I have a little swamp cooler that is big enough to fit 2 glass carboys. I currently have one carboy filled and will stay in primary in the cooler (@64F) for 3-4 wks before bottling (no secondary). I'd like to know whether I can pull the carboy out of the swamp cooler after 2wks (after confirming FG has been reached) and let is rest (condition?) at room temperature (71-72F) for the remaining 1-2wks, thus freeing up space for two new brews that I want to make to go into the swamp cooler?

Secondary @ 72F for a couple of weeks is fine IMO...

You'll be fine. I do the same thing. I take the primary out of the swamp cooler after fermentation is complete and let it mature at slightly warmer temperatures. Then my next batch goes into the swamp cooler and the cycle repeats. Especially if the beer is only at 72, you have nothing to worry about.

Letting your beer gradually warm up to 70ish after 3 or 4 days of fermentation is a good thing. It keeps the yeast active, which cleans up biproducts of fermentation and residual sugars. As other posters have stated, you'll be fine.

Is there any evidence to support the theory that higher temperatures help the yeast to clean up by-products of fermentation?

Yes, research "diacytel rest". Yeast generally start going dormant and flocculating when there is less sugar to consume. Slowly increasing temps keep them from passing out so soon.

Thanks Bobby, I've heard the term diacetyl rest, but always in association with lagering. I'll have to research further.

A question I have is, if the yeast becomes more active at the higher temps, then what's stopping the formation of undesirable esters that typically happen during primary fermentation at higher temps?

The esters are formed primarily during the growth and reproduction phase, i.e., after you aerate and pitch. That's why lager brewers can do a diacytel rest and not risk extra ester formation.

Correct me if I'm wrong, but I also believe yeast metabolize esters, amongst other compounds, at the end of fermentation as well, before going into hibernation mode. So even if too many esters are created early on, they get cleaned up later to a large degree provided they're not shocked into hibernation mode by a temp decrease.

I remember Jamil Z stating in one of the Brew Strong episodes that for many beers, once the reproductive stage is over, the actual temp of the beer is not as important as the slowly increasing temp, within reason. I think this cleanup process at the end is the reason why.

At any rate, the two big problems with fermentation temp that have adversely affected my beer (that have stuck out to me) are high pitching temps and low, or unsteady, finishing temps. Either one of those is sufficient for a batch to be a little off in its flavor, or at least not as good as I expected it to be. Other temp issues seem not to play as large a role in the overall quality of the finished product.

what is the highest temp you can have while conditioning? till winter really hits its been getting up to 80's in my house during the day and then cooling down to low 70's at night.

I've conditioned in the mid to high 70's routinely with no problems. I believe warmer (70's) is definitely preferred to cooler.