Could be one of the many chemicals involved in its installation. Spray adhesive, PVC primer or glue, duct sealant. If this is a new system retrofitted in place of an older one, the smell is likely duct mastic applied to the inside of the plenums to seal them. The smell will fade in time. It's not hazardous at all. If it's a totally new house, with all new equipment and flex duct, the new flex duct will have a plastic-ey smell for a while, after all, its made out of plastic.
Propane has been given a sulfur-like smell for leak detection.
Presence of sulphur.
Cobalt(II) chloride may be a reactant in a chemical reaction.
chemical change
An alteration of a substance that does not affect its chemical composition. A change in size and shape would be an example.
Low antifreeze might cause an intermittent chemical smell from the A/C on the recirculate mode. The recirculate mode is a feature of some diesel engines so that all of the air cleaners can get blown out. Perhaps the dirt is causing the chemical smell.
Changing ac components under the hood should not cause a chemical smell. If the smell changes by changing the air settings from recirculate to fresh, then there may be some chemicals on the outside of the parts. It is also possible that you damaged a part of the heater core system and the smell is antifreeze.
detect smell
If you smell antifreeze, there must be a leak somewhere. Have the cooling system pressure tested.
Bacterial, chemical
It is a chemical change because you cannot not make the smell go away, if you could it would be a physical change
A chemical system consists of the system and the surroundings. If you're dealing with a solution in a beaker, the solution would be the system and the beaker and air would be the surroundings.
you would be able to see or smell the change
There are numerous possibilities. You really need to have the cooling system pressurized to determine what is leaking.
A chemical reaction is what takes place when two or more opposing chemical come together and cause some sort of reaction, either positive or negative. An example would be mixing bleach and ammonia which will trigger a very noxious smell which can lead to serious illness.
cause its weird
This would depend on your nose. A bad CMP sensor may cause improper burning of the fuel and can give a smell out the tailpipe. Will the CMP smell? Never. A Ford camshaft syncronizer will squeek and could cause a metallic burning smell.