list produces a list for a certain field. If there are multiple values in that list, timechart would have no way of knowing what to do with that, so it doesn't make sense for timechart to accept values from a list.
What is the reason for using list, and in what cases does it produce multiple results? If I were to go about this I would want two fields (apart from the timestamp): one for the temperature, and one for the location. In an example, let's call them temperature and location.
Now, some explanation on how timechart behaves: timechart needs some kind of statistical function that returns a unique value for the timespan it's operating on. If you don't define the timespan yourself it will be set dynamically depending on what timerange the whole search spans, but let's take an example where the timespan is 1 minute and that somewhere in your log you have 3 temperature readings from a certain sensor occurring in the index within 1 minute. Splunk needs to know how to give you ONE value for "temperature", even though there are 3 values of each. You can tell Splunk to just give you an average from the 3 events using the stats function avg:
... | timechart span=1m avg(temperature) as Temperature
Or, if you only want the values from the first of the events within the time period, use first instead of avg. Want the sum? Use sum. And so on. More information on statistical functions is available here: http://www.splunk.com/base/Documentation/latest/SearchReference/Stats
To make it do this split by location, just add a by directive at the end of the timechart command:
... | timechart span=1m avg(temperature) as Temperature by location
