OK, it wasn't HVAC but I did do in home service for a major appliance manufacturer. 99% of service techs take as much pride in their work and reputation as everyone else but they are human and DO make mistakes.
What it sounds like to me is either one of two things:
Scenario 1 - One of the replacement parts didn't wire up exactly like the original. Manufacturers will change suppliers sometimes and while the replacement part looks the same, it may wire up differently. Sometimes you get instructions with the part as to what has changed, sometimes you don't and if you DID get instructions they are clear as mud with pictures to match. And of course the schematic provided with the original unit doesn't match what you have in your hands so it can be a guessing game.
Scenario 2 - There were more terminals than wires, tech 1 didn't diagram each wire and terminal and wound up putting a wire on what should have been an open terminal.
I've had a combination of both scenarios, especially on microwave oven capacitors. The original had one terminal for each wire (two wires, two terminals) but the replacement had 4 terminals for two wires (grouped one terminal for wire A and a choice of THREE terminals for wire B). The schematic was useless for that part because it only showed 2 wires and 2 terminals.
Since tech 1 came back a few days later and made it right indicates to me he ran into another situation like yours and once he found the issue he figured out the problem with yours. If he was intent on screwing you, he would have just said "Hey I got my $75, let them worry about it. If anyone asks, it was a simple mistake.". I saw plenty of that after homeowners called "Joe's Appliance", paid twice what factory service would have charged, it still wasn't fixed and the servicer would not come back out or return calls. Imagine what fun THAT scenario is to walk into...
Tech 2 sounds like he poked and prodded around but didn't do a THOROUGH re-diagnosis. There were only 3 techs I implicitly trusted the diagnosis of if I went back out behind one of them, usually to install parts, and one of those 3 techs was my Dad. Anyone else and I would go through my own diagnosis to make sure we were looking at the correct problem, regardless of what the tech told the homeowner or what parts were sent out. Usually the diagnosis was correct but sometimes the parts ordered weren't going to solve the root issue.
Yes, mud duabers can short a contact. Any critter that gets between or builds something between two contacts will cause a problem. I've had two cases this year like that. In one, a mouse got between L1 and L2 of a dryer teminal block and created a direct short. Messy.
![Laughing :lol:](./images/smilies/icon_lol.gif)
In the second, it was an 8-10" snake that did the same thing.
As far as the difference in pricing, it's up to the individual company what they charge for labor. AFAIK, there's no "Labor book" like what I've always been told mechanics or car dealerships use. My employer told me what I was to charge per hour or per repair and there was very little leeway (senior discounts, etc). Since both were going to cover the parts under the manufacturers warranty that tells me the manufacturer will reimburse them for the cost of the replacement parts.
If it sounds like I am defending them, I am
to a certain extent. I've BTDT, gotten a couple of t-shirts and taken the verbal abuse. I DO NOT condone lazy diagnostics or attempts to defraud a customer. I DO understand that techs are not machines with a computer brain that has the answer to every scenario.
As much as we dislike it, sometimes we just have to say "I don't know" but in my world that better be followed up with "But let me see if I can find out".