I am seeking advise on what is the right approach.
I had an HVAC technician come out and replace refrigerant in one of our AC units (this was done through home warranty company).
I then had another company come out that was not linked to home waranty company and had good ratings in our area, this was after an issue with the other AC Unit. The second company told me that anytime refrigerant is exchanged a drier has to be replaced as well (to prevent moisture) Now the cost of this service is ~$300 (sounds like for refrigerant exchange+drier). I called the original HVAC guy and was told that they don't change drier with refrigerant exchanges. That the reason I was told to change it is because the other company makes more money by doing services that are not necessary.

So who to believe?

 

What is a refrigerant exchange?
Any time the system is opened to the atmosphere the drier should be changed.

 

Exchange ? Do you mean refrigerant added to a working system ?

 

One of units was "low on freon", unit was "recharged" with Freon 410a. The HVAC company (through home warranty) that did this recharge did not replace the drier. When I asked them about this they said they do not replace drier when they recharge. I'm not sure if the system was opened to the atmosphere when a recharge is done.
But the the other HVAC company with much better reviews said it is standard practice to do so.

 

You don't just add refrigerant you look for a leak. Did the Home Warranty HVAC company do that? I''l bet they didn't because they are working on very slim profit margins.

 

Low on refrigerant does not require a filter replacement.

Only when there is 0 refrigerant in the system for an extended period of time or the system is cut open is a filter/dryer replaced.

 

My question is where the Freon went, Freon does not get used it has to leak.

 

Refrigerant is not a consumable material. If the charge was low, you have a leak and the refrigerant will leak out again.
It is not good for the unit to operate while low on charge. It can cause serious compressor damage.
It is not surprising your home warranty is doing substandard work. They have long been known to do such things.

 

After the first service where they replaced the freon AC worked for 2 days then began blowing hot air. They came out a second time and determined that evaporator coil (located in attic) had a leak and replaced the evaporator coil. After the replacement the AC unit works fine.

 

When they replaced the evaporator coil.... then the filter/dryer should have been replaced with it. The sealed system was open to the air.

 

Which answers the question did they check for a leak as they should have the first time. That sounds like a big leak to last only two days. Guess they didn't want to go into a hot attic or spend the time looking for leaks.