Blood Bikes Wales volunteers help the NHS by delivering emergency blood, donor milk and medical equipment between hospitals.
The family said: “Helping people and volunteering as [a] street pastor for many years, Andrew had a strong Christian faith, with his life guided by his lord Jesus.
“Andrew was a farmer his whole life and it was his passion. He was well known, loved, and respected within the farming community and extremely knowledgeable.
“[This] knowledge he passed down to his children and grandchildren over the years.”
Dyfed-Powys Police said the 26-year-old man driving the Audi was arrested on suspicion of causing serious injury by careless driving.
He has been released on bail while the investigation continues.
The force are appealing for witnesses.