Put liquid yeast in wort cooled to 70 degrees. My yeast was at 78 degrees not 70 degrees no bubbles yet.
If it is still not bubbling or showing positive signs of fermentation then IMHO the yeast should be re-pitched ASAP. This time make up a starter to check the yeast to be pitched is actually active before pitching it. I would also recommend that (at this stage) a double dose of yeast is used (eg 2 packets not just one). The priority is to get this brew fermenting in bulk before something else does that for you.
48 hours is usually a long lag time. But not always.
For more detailed answer please post your wort OG, yeast type, yeast date, amount pitched, storage conditions of yeast, how was wort oxygenated.
I would keep it below 70° though, in all cases.
This may just be lost in language, but yeast needs to be added after wort has been chilled to pitch temp.
I would also have to ask if you are certain the seal for your lid/cover is working 100%? I recently assumed that a saison I had just created wasn't fermenting and discovered that the gasket on the lid of my fermenter wasn't properly aligned and was allowing C02 out so there was no activity in my air lock. A quick fix and all was well.
In other words - check your setup and do not assume.
Can you observe a krausen on the top of your beer?
I agree, 48 hours, you should probably see something indicating that fermentation is taking place. No foam, no bubbles, however slight? Some yeasts are quite temperature sensitive, requiring a specific range to activate and work properly, however, I don't feel that 78F would be too high to kill most yeasts.
If your liquid yeast was outdated or improperly stored, it may be bad. You can add a bit of yeast nutrient and/or energizer to give it a helping hand and see if that stirs things up.
Did you oxygenate your wort with either an oxygen tank or serious stirring? Maybe that's an issue contributing to the slow start.