The recent openHAB 2.3.0-SNAPSHOT builds (#1230 or newer) now support units (see announcement). So it now possible to use the updated Nest Binding (PR #3150) that natively supports Fahrenheit temperature values.
Here is a org.openhab.binding.nest-2.3.0-SNAPSHOT.jar for people who want to help testing this PR.
You’ll also need to update your Nest temperature item definitions. See the updated README for some examples.
What kind of error messages do your logs show? I’ve made a fix in the updated Nest Binding (see text above) so it can handle missing values due to missing permissions or older API versions. Any missing values will now be updated to null instead of throwing exceptions.