Question with proper condensation traps

[channelislands]

Okay little embaressed as a tech to ask this one, sure there have been threads about this but need to resolve some questions. Heat Pumps require a J trap to build negative pressure in line to keep condensate from blowing into cabinet and out of primary pan correct? Furnace's do not require traps due to position of coil being past heat xhcanger and away from blower correct?
And as opinion, when I go to a call and see that the secondary line is piped into the primary, I abandon the secondary and install a float switch instead. Reason being if the primary line is blocked the secondary is draining in same line obviously its just going to cause a flood. Do you abandon the line install a float switch? Or do you take the time and pipe the secondary into its own line?

[yorkdude]

You only need a trap when the condensate line is on the pull side of the fan. On upflow furnaces the condensate line coming off the coil does not need a trap ....its on the blow side. Thats how i always do it. And yes, use a secondary safety switch.

[beenthere]

As far as running a new line for the secondary on an existing system. Varies with the house.
Usually end up with a switch.
I like traps on positive pressure coils also.

[channelislands]

thanks its so hard to remember all of the ac stuff especially when you work on just about anything

[Glennhvac]

You only need a trap when the condensate line is on the pull side of the fan. On upflow furnaces the condensate line coming off the coil does not need a trap ....its on the blow side. Thats how i always do it. And yes, use a secondary safety switch.

wrong. sometimes they blow so much the condensate just swirls around. Put the trap in and spend the extra $1.15