In the heating cycle, you don't want the fan running much at all after strips/heat pump shuts off. No more than 10-15 seconds. I have also had our installers not connect the high voltage properly when changing an electric heat air handler. Depending on the heat kit they put in the air handler, it may run off one 220V circuit or it may require two 220V circuits. It is a common screw up on change outs with air handlers. So the installers, in all their infinite wisdom, will simply hook up one set of strips and not hook up the others. This can leave the fan thinking the unconnected set of strips is still on. Thus, the reason the fan is still running so long. My bet is that a set of strips are not connected or they put a smaller heat kit in than what you had before. I hope they are honest with you if this happened because you are at their mercy unless you get some other company to come look at the install.
I have no idea what your set up is but to further clarify. All air handlers are supplied with no heat strips. We order the "heat strip kit" separately from the air handler, depending on what the high voltage electrical to your air handler requires. But just take a 4 ton air handler for example. Let's say your air handler has a single 100 amp 220V circuit feeding it. Typically, it would use a 20 KW kit. 4 heat strips. Each strip pulls 20 amps. I can order that kit as a single circuit kit for your 80 amps worth of heat strips. I can also get the same 4 strips in a kit with two separate circuits, 40 each circuit or 60 on one circuit and 20 on the other circuit or even 2 strips at 40 amps each. The reason all those add up to 80 amps is the fan motor will come on with one of those circuits and accounts for the missing 20 amps in my examples. The motor doesn't pull 20 amps but you need the extra 20 amps as wiggle room in total amps pulled. The kit I order depends on whether you have a single circuit of 100 amps or two circuits with that 100 amps divided between the two. This same situation applies to all air handler sizes. Sometimes a company will replace your old 4 strip unit with a 3 strip kit for your new air handler. It can be done a myriad of ways depending on the way they decided to set it up. But the single restricting factor is the high voltage circuit supplied to your existing air handler at the time. Is it one large circuit or two smaller circuits? Hope I did not confuse the issue. I was just trying to explain how the kit could be different than what you had and this will affect the units operation. The blower fan is either on the one single circuit kit or if it is a two circuit kit it is on one of the two. In any case, the fan won't shut off until it knows the last strip is off. It sounds like your fan thinks one or more strips are still on for that 2.5 minutes.
This is not typically something we discuss with the home owner because it is more of an application issue than an optional issue. It is our job to match equipment to electrical supplied. If we get it wrong, we get situations like yours and have to replace the kit with one that matches your existing wiring without overloading the wire\breaker size.
If you can tell me what size unit you have and what size breaker in your panel is feeding it, one breaker or two separate breakers, I can tell you specifically what has happened that is creating the issue. I have to go to work at 10:30 this morning and won't be back until around midnight. So I will reply later if you need more clarification.
