replacing ceiling fan with only 2 older wires in ceiling

So, stupidly I didn't take a shot of what was there before.
I tried testing the two wires by holding a simple voltage tester. Each lights up only when both are touched and they look exactly alike. Can I use them interchangeably safely?
Do I attach both the blue and black from the fan to one from the ceiling and the white to the other one?

 

You need a real tester, not a non contact tester, either a multimeter or neon test light.

If you have a house ground at the light using a multimeter test each wire to ground. The one that shows ~120 volts is hot.

If no house ground you will need a grounded extension cord plugged into an known correctly wired receptacle*. With the switch on test from the wide slot of the extension cord to the each wire. The wire that shows ~120v is your hot. The remaining wire is neutral. Connect fan black and fan blue to hot. White to neutral.

*You can also use a polarized non grounded extension cord.

 

thanks ray- will follow the steps you've provided!

 

Correction it must be either a grounded extension cord or a polarized extension cord. I have corrected the omission in my preceding post.

 

ok. got it........ thanks

 

What kind of junction box are you using?

 

hmm- not really sure how to answer that question- it's the existing one that was there for the previous fan. The other fan worked (spun, light worked)- it just got overly wobbly and all attempts to fix were fruitless.

 

So- getting to this now-
I am supposed to insert the wire I'm testing into the larger slot on the extension cord? Where do I place the probes from the multimeter?

 

NO. That could be a dead short and big boom. Follow the logic of what you are doing. You are checking each wire to neutral of the extension cord. One probe to the wide slot of the extension cord and the other probe to the wire being tested.

The box does not seem to be flush to the ceiling, is it? Does it use 10-24 fixture screws to hold the fan bracket? If it uses 8-32 it is not rated for fans.