Been trying to pick up parts at the junkyard to replace broken plastic parts.

My problem still unaddressed is I took the car for repairs as it was stalling & they changed the fuel relay. Anyway on the way home the AC would not blow cold as it always had. I was thinking somehow when they repalced the relay something happened to the AC but I have been told the ac re;ay is uner the glove compartment.

I have not checked fuses or relays as they are not that easy to get access to.
The AC blows heat ok.

Anway are there parts for my 127 K volvo that would be good for me to buy used if I found a low mileage donor?

picked up a ignition module & idle control alve as they were easy to get & sort of looked good.

I also got a master door control switch as my rear pass window button won;t work in the up.
I heard it could be cleaned but I took one apart at the junkyard & all the balls fell out.
Not easy.
Also I am still confused about dielectric grease.
Is this good & recommended to put on metal parts of switch prongs or fuses to keep a good contact or does that impede contact.

Whats the best thing to use when installing small metal parts with prongs & plugs..

Thanks