Lubavitch institutions do not conduct conversions. I read somewhere that it is because of some agreement between the Lubavitcher Rebbe and Rabbi Moshe Feinstein.
Why does Chabad not "do" conversions?
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A Chabad rabbi is not necessarily a Rav. Most who are running Chabad houses are not. Additionally, they understand that to be fair to the people who want to convert they should ideally do so with a beis din that will universally accept that geirus including in Israel without any religious politics getting in the way. It should be noted while a Chabad Rabbi might not be in the converting beis din he might be the sponsoring Rabbi that helps the person reach out to the people who will be in charge of the conversion.