The first time he had any trouble with the new arm was during a mission in a town on the outskirts of Houston.
It was a simple mission. Him and Sam were meant to scope out the area, see if anything weird was happening at the diner next to the motel they were staying in.
Weird, as in, was the diner just a front for HYDRA or other evil organization's labs or recruitment or was it a real diner?
On their second day there, they're lending more towards the former.
As him and Sam swallowed down their charred burgers and undercooked slivers of potatoes the dinner dared called french fries, in what they had deemed a makeshift date, Bucky could hear the waitress pace nervously around in the walled-off kitchen. An advantage of the knockoff serum, of course, had been increased hearing. Sometimes it could be obnoxious, but sometimes it could be helpful, so he's not going to complain about it.
The waitress, with her platinum blonde hair and uneasy smile, was the only person they'd encountered at the diner. They'd been here last night, too, and she'd been the one to seat and serve them just as she had done tonight. Both times, him and Sam were the only customers in the diner. Either it's that much of a small town or the residents know the food is terrible and steer clear.
Maybe it's both.
As he was nibbling on a french fry, he heard another set of footsteps join in with the waitress's pacing.
He kicked his leg into Sam's shin, a knee-jerk reaction to the addition of the new footsteps. They weren't talking, or at least Bucky couldn't hear them.
"Ow! Man, what the fu-" Sam yelped, cutting himself off when he said Bucky pointing accusingly at the wall separating the dining room from the kitchen, and then held up two fingers.
'there's two?' Sam mouthed, and Bucky nodded.
Just as Bucky was getting ready to respond, it went back to only one person's footsteps and the waitress came out of the kitchen door a moment later, her hair a little disheveled.
"You both done?" She questioned as she fixed stray hairs back into her ponytail, taking the plates from them before they had a chance to respond.
She pulled a check out of her apron, along with a pen.
"Handle this when you're ready." She nodded to them, then took the plates back into the kitchen.
"What, no asking us if we want coffee or dessert?" Sam commented in a disapproving whisper, shaking his head as Bucky pulled a twenty dollar bill out of his jeans' pocket and set it on the check.
"Let's get out of here before they start shooting." Bucky whispered back. The twenty would cover their meal, and whatever organization is running this place can keep the charge. He's pretty sure that waitress was a word away from pulling a gun out of her apron instead of a pen.
They slid out of the booth and made their way to the glass door that served as an entrance, quickly tiptoeing out of the place and out into the hot, blazing weather of Texas in the middle of July.
Immediately, Bucky felt like he was on fire.
Surprisingly, he hated higher temperatures more than lower ones. Sure, the winter months kept him on the edge of a panic attack because of flashbacks, but the cold was familiar, at least.
The heat wasn't.
The worst part was the vibranium of his arm felt as though it was sizzling with warmth. Just a few seconds in the sun and the arm felt like it was overheating, in a way that it never had before.
The arm's excessive heat was making his entire body hotter, and by the time he and Sam returned to their motel room, he felt as though he was covered in sweat.
Once the door was locked, Sam turned around and locked eyes with Bucky, immediately realizing that something was wrong.
"Are you okay?" He asked, and Bucky just swallowed and nodded, the air conditioning in the room blowing over him feeling like the biggest relief.
"Yeah. Just...hot." He said, blinking dark spots out of his eyesight. "I'm...gonna go shower."
Sam didn't question him as he retreated to the ensuite bathroom and closed the door.
Bucky relaxed under the freezing stream of water, finally cooling off.
A few weeks later, it happened again, but in the opposite temperature.
Him and Sam were on a mission in Canada. Snow covered all they could see as they exited the abandoned HYDRA base they had just inspected.
Bucky vaguely remembered being kept in this base between missions a few times. There was a room they assumed was used to be used for cryofreeze, although there wasn't a cryofreeze chamber in it, leading them to suspect it had been removed before the base was evacuated.
They found a few files. Nothing substantial. A few holding records of the Winter Soldier, as well as a few agent reports. They'd file them away in the databases, just in case they could ever be of use, but the mission was mostly a bust.
Now they were just waiting for extraction.
"I've got your coordinates. Extraction ETA is three minutes." Sharon spoke from the comms line.
"Thanks, Shar. You're the best." Sam replied.
"I told you to stop calling me that, Wilson." She said harshly, but Bucky could tell she was smiling through the comms line.
Bucky exhaled, watching his breath turn into a little white cloud from the cold.
His entire body was freezing.
His metal arm felt numb. He wasn't sure if it was the sensation sensors malfunctioning or if it was the cold that was causing it.
He started shaking by the time Sharon said their extraction was a minute away.
Sam noticed his behavior, the shivering and clattering of teeth, and quickly moved to wrap his arms around his boyfriend.
Despite the fact that Sam had been out in the snow for as long as Bucky has, he's warmer. His chest feels like a radiator, and Bucky soaks up heat like he hasn't seen the sun in decades.
"Thirty seconds out." Sharon reports, just as Bucky hears the whirling of a helicopter engine in the distance.
It gets closer and closer until it's deafening, and then the helicopter hovers over a patch of snow and the entrance on the side slides open.
Sam helps Bucky walk towards it, a hand over his shoulder and another on his waist, steadying him.
Once they're safely in the helicopter and seated behind the pilot, and Bucky is slightly warming up alongside his arm, Sam finally speaks again.
"Flashback?" He asks quietly, as if fearful to pull on that thread.
But Bucky just shakes his head. Surprisingly, seeing the holding files and going through a base he knew his body has been to before evoked nothing of the sort.
"Cold-induced panic attack?" He tries again, a slightly frown on his face when Bucky just shakes his head again.
"Then what's wrong, man? Are you sick?" The back of Sam's hand flies to Bucky's forehead, as if trying to take his temperature.
All his hand feels is a freezing chill.
"It's...it's, uh, my arm." He gestured vaguely. "It's changing temperature too fast. When it's hot outside, it burns up and makes me feel like I'm blazing. When it's snowing it makes my arm freeze and makes my entire body feel like a popsicle."
Sam's face twists into something unreadable, but Bucky can tell it's at least an expression of sympathy.
"Buck…" Sam pulls him into an awkward hug in the helicopter seats. "You should've told me. We can call Shuri, she can take a look at it, get you all fixed up." Sam soothes, rubbing circles into his boyfriend's back. "It's gonna be okay."
Bucky nuzzled his head into the crook of Sam's neck, once again grateful for his boyfriend's body heat. "I love you." He whispers out, and he can hear Sam smiling.
"I love you too."
"I thought I had programmed the thermoregulatory system in your arm to alert me when it began to malfunction." Shuri sighed in frustration. "When was the first time you noticed it was heating up or cooling down too quickly?"
"Uh, during an undercover mission." Bucky answered truthfully. "Investigating a diner in Texas."
Bucky sat on one of the exam tables in Shuri's lab, legs swinging off the side as Shuri scrolled through her files on a holoscreen. Sam was next to him, a hand on his flesh shoulder for support.
"Is it possible they had use of any kind of signal disruptor?" She asked. "If the signal was blocked, I wouldn't have gotten the proper alert."
"It was run by old HYDRA goons." Sam cut in. "I don't remember exactly what kind of operation they were running, but they easily could've had a signal disruptor."
Shuri nodded. "Most likely." She moved her holoscreen to the side with a flick of her finger and turned to face Bucky. "Alright. To fix this I'll need to remove your arm completely and then see exactly what I'm dealing with. The scans have shown me nothing but that something is malfunctioning. I'm unsure how long it'll take to fix until I get in there. I'll turn your tactile sensors off, followed by your sensation sensors, and then I'll be able to remove it without any semblance of pain." She explained. "Sound good?"
"If it'll fix my thermo-whatever, yeah. I'm good." Bucky confirmed.
Sam held his flesh hand as Shuri shut down the sensors, before using a few tools to remove the prosthetic from his residual limb.
"Alright." She said, finishing with peeling off the liner that protected the skin on his residual limb from irritation due to the prosthetic. "All done. I'll work on this for a bit. You two lovebirds can go around the palace or out into the country or wherever the wind takes you. Just be back by sundown." She lectured as if she was a mother watching her kid go on their first date.
Bucky ended up going back down to the village he used to reside in, dragging Sam along with him. He introduced Sam to the goats, tried to get him to read one of them a bedtime story. He refused, but that didn't mean Bucky didn't catch him singing nursery rhymes to one of the kids.
When they returned to the palace and to Shuri's lab just after sundown, she was working on something entirely different to the arm, which was sitting on her workbench, sparkling as if it had been freshly cleaned.
"Look who's finally back." She teased, putting her other project down and patting the exam table Bucky had been on earlier.
Bucky sat down as requested as Shuri picked up the arm again, pulling up her scans and a command center.
"The malfunction was minor, but was causing major problems. A simple few wires to fix and everything was back up and running as it's supposed to." Shuri reported, one arm holding the heavy metal object and the other one swiping through scans of the arm.
"I also put in something that should prevent signal disruptors from affecting it ever again." She added with a cocky grin. She was a genius and she knew it. "You ready to be attached again, Bucky?"
"More than ready." He responded, and her grin grew even wider.
She put on a new liner over his residual limb, before slowly slipping the prosthetic into place. She used a few tools to secure it in place to his shoulder, but nothing that caused him any discomfort.
"Alright." She turned back to her control panel. "I'm going to turn on the sensation sensors now, okay?"
A warm tingling spread through his arm in the span of a few seconds, before disappearing.
"Turning on tactile sensors." She warned just as the sensation had stopped.
He felt nothing that time, but when he brushed his metal fingertips across the soft sheets on the exam tables, he could swear he felt every single thread.
"Working good?" Shuri questioned, which was met by yet another nod from Bucky.
"Perfect." She pulled the holoscreen down, causing them to fade into thin air. "Now, I'm going to go steal a snack from the kitchen. Would you boys care to join me?"
After their snack run, they left on the same quinjet they arrived from, and flew back to the base in the States with the promise that Bucky would tell her if something felt wrong again.
He wasn't sure if he could uphold that promise well, but he could at least try.
Luckily, whatever Shuri had fixed worked wonderfully. His arm didn't go too hot or too cold too quickly, and it certainly didn't impact his body temperature drastically as it had before.
He can lay under copious amounts of blankets to cuddle with Sam and not worry about overheating due to his arm. He can handle a mission in the snowy mountains without too much shivering.
It had been an unpleasant few weeks before the malfunction had been repaired, when he'd been too stubborn to admit something was wrong.
But everything is okay now, and he's got the best boyfriend ever to who truly loves him, helps him through things and coaxes the stubbornness out of him.
And that was really all he needed to make him happy.