Checked my AC via sight glass...
 

Today I ran my AC and checked the sight glass... I got lots of bubbles until I rev'd the engine and held it (not sure what RPM but am guessing between 2500 and 3000) there. The bubbles went away until the electric fan kicked in, once it was on the bubbles reappeared. Once the fan cycled off the bubbles went away... is this normal?

to cold outside to check it
 

Hello 190D22
A sight glass is not effective below 70F..
You are wasting your time.

The sight glass has some uses... however they are never definitive. It is still valuable... if you know what the limitations (like the one Whunter mentioned for instance) of conditions and refrigerants are...
There is plenty already posted about the sight glass useage if you do a search...
With regard to bubbles the rules are different with R134a as compared to R12.

Whunter and Leathermang, mention that the rules are different for R12 vs. R134, and that the sight glass is not a good indicator when the ambient temperature is below 70F. What are the differences that one will notice in the sight glass between these two gases?

Its now 35F outside here in Montreal, and I noticed bubbles in my car as well ('95 E300 Diesel with R134) I am therefore wondering what the bubbles in the sight glass indicate.

Will these bubbles disappear once the ambient temperature reaches 70F?