All perfect praise be to Allaah, The Lord of the Worlds. I testify that there is none worthy of worship except Allaah, and that Muhammad is His Slave and Messenger.
The Hanbalis, like other scholars, hold that Ijmaaʻ (consensus of opinion) is valid evidence. All the Hanbali books of Usool Al-Fiqh mention the authoritativeness of Ijmaaʻ and they also use it as evidence. You are advised to refer to some of these Hanbali books such as Sharh Mukhtasar At-Tahreer by Al-Futoohi, Sharh Mukhtasar Ar-Rawdhah by At-Toofi, Ar-Rawdhah by Al-Muwaffaq Ibn Qudaamah. What has caused some people to have made such claims may be that Imaam Ahmad famously said, "Whoever claims Ijmaaʻ is a liar." Scholars have explained the intended meaning of that statement and underlined that Imaam Ahmad did not mean to negate the authoritativeness of Ijmaaʻ by this statement.
Al-Qaadhi Abu Yaʻla wrote, “What is apparent in this statement is that he negated the authoritativeness of Ijmaaʻ; however, this was not the intended meaning. Rather, he stated so out of caution, as there might be a different scholarly view that a scholar has not heard about, or he may have been referring to when the scholar is unaware of the difference of opinion among the righteous predecessors on any given topic, because he (Imaam Ahmad) explicitly declared the authoritativeness of Ijmaaʻ in a report (from him) by ʻAbdullaah and Abu Al-Haarith. He also claimed an Ijmaaʻ in a report by Al-Hasan ibn Thawaab, saying: "I believe that the Takbeer should start from the early morning of the Day of ʻArafah and (should proceed) until the last Day of Tashreeq." When he was asked about the evidence concerning this, he replied, "The Ijmaaʻ of ʻUmar, ʻAli, 'Abdullaah ibn Masʻood, and 'Abdullaah ibn ʻAbbaas.” [Al-Musawwadah]
Therefore, it is clear that the Hanbalis hold Ijmaaʻ to be authoritative, and whoever claims otherwise is mistaken.
Allaah Knows best.