If the condensate is piped to a drain connected to a sewer system with either a dry trap or no trap, the fan could induce the flow of odor into your air handler.
Pour some water into the trap.
By trap I mean a loop in the piping that will retain an amount of water to act as a seal.

can you take a picture of the condensate, and what the tech did? I'll bet you have an open sewer line connected to it.

It is unhealthy to have your a/c draining into your sewer or sewer vent piping.It is a code violation as well and should be corrected.The smell is Methane gas from the sewer amoung other things.

A heat pump should be treated with algacide tablets placed in the indoor coil drain pan area Because :
Over the summer months algae forms in the coil drain pan in addition to the Indoor coil fins as the coil stays 40 degrees while in the cooling mode.
During the Heating season the same coil and pan area stay very hot , while in the heating mode. This cooks the algae and creates a objectionable odor in the conditioned space.
Be sure to replace the filter when it becomes dirty ...above all be sure to turn the unit off when changeing the filter as to avoid dust from going into the unit.
Have the contractor provid a drain outside known as a french drain or dry well the spec's are on the web.

Googe

Instead of a 3000 dollar french drain, you can get the contractor to install a small condensate pump that has a 3/8" plastic tubing that can run out with the copper linesets. This will get the line out of the sewer line, and should only cost around 250.00