A heating techniction may have caused my heat exchanger to crack...? ?

Explain the non compatibility issue please. Becouse I don't understand why that would be. 

Heat exchanges do crack, may or may not have anything to do with last years tech. This one is saying you need a new tank and a new furnace, I'd be getting a second opinion.

First of all how do you KNOW the heat exchanger is ACTUALLY cracked?

Without tearing the furnace apart and using a camera, it's impossible to tell.

Blaming a cracked heat exchanger is the oldest scam in the HVAC business.

That way they can sell you a new furnace and central air you don't need.

My furnace is 58 years old and my heat exchanger is fine although several crooked furnace techs tried to say it was cracked and i needed to buy a new system.

Naturally they didn't show me any pictures, video, or proof so i told them take a hike.

I bought my own video inspection camera for $59 and unlike the furnace con men i fully disassembled the back of the furnace then carefully looked at every square inch of the heat exchanger and of course found NOTHING.

And yes, the explosion COULD have caused damage to the heat exchanger, burners, flue pipes, AC evaporator, etc.

IT may have been caused by the previous technician (or just old age) but it is way to late to do anything about it now. Should have addressed the issue with the company that sealed the vent closed and had a second company come in and inspect for damage right after the explosion. 

yes.  the explosion and violent across the room throwing of the heat exchanger could well have damaged it.  alas, the time to inspect it was immediately after it happened.  you're unlikely to get much out of that company now.  Assuming your approaches to them are ignored or rebuffed, I suggest the following ideas -- a) hire a solicitor or attorney to sue them, and/or b) make sure to post multiple nasty reviews citing their person's ignorance and malfeasance which caused damage ...

That sensor will shut down the furnace if it is disabled or clogged.

So will a flame rollout sensor.

It would be hard to prove he was the one who did it, after a year.

His counterclaim is that he didn't do it, and YOU did.

The explosion may be caused by something unrelated to that sensor.

One or two of the burners might not have lit when the furnace came on and spewed fuel into the heat exchanger. Another one that did fire probably caused the fuel vapors to ignite and explode.

No way to really know for sure.

About your A/C.

You can have an air handler installed just for that and not have to spend massive cash on a new system.

Air handler is just two plenums, your evaporator coil, drain line, blower, and some wiring to tie it in.

Same principle as a dual furnace setup except the heat part is in a different air handler.

You could also get mini split systems too, which can be cheaper on the utility bill if you use them appropriately (manual zone control).

Just so ya know:

Unless your furnace is really old, heat exchangers can be replaced. If this is done, ask nicely if the repairman can spray PAM on the new gasket (keeps it from shrinking and very hard to burn VERY). Makes the gasket easier to remove in the future.

Same with a draft inducer gasket. PAM!

Also, if you have insurance, check your policy. If you have home warranty insurance, check that policy.

I would say yes, there is a very good chance.  

What you need to do is have the current company evaluate your system. Explain what the previous technician did ....and have this current company supply you with probability as to the cause....and effect of the explosion on the heat exchanger. Maybe it will go somewhere ...maybe not, but it's worth a try. Any pictures you have would be helpful