Stay away from R10.4.0 for now at least for 1534P switch - I have it working on two 1638Ps with no fan problem. I discovered that when you downgrade to R10.3.1 nothing happens and the fans are still stalled but if you downgrade and hard reboot (pull the plug) the next time switch boots up everything is working correctly.
It has recently been discovered that running R10.4.0 on 2nd Generation NetVanta 1534s and 2nd Generation NetVanta 1544s could cause the chassis fans to function improperly. Without these fans working as intended, the switches could eventually overheat and become damaged. As a precaution, ADTRAN has pulled this firmware from the website for both of these products.
Until this issue is addressed, ADTRAN recommends running AOS version R10.3.1 or any other previous software revision on these switches. This issue will be resolved in the next feature release available for the 2nd generation 1534 and 2nd generation 1544, which will be R10.5.0. This software is tentatively scheduled for release on November 12. If you are using features in R10.4.0, most notably AWCP for NetVanta 160 APs, and cannot delay using these features until the next release, please contact ADTRAN Support for a temporary engineering build you can run until R10.5.0 is generally available.
We apologize for any inconvenience this may cause you. If you have questions about this, please contact ADTRAN Support by sending an email to email@example.com , calling 888-423-8726, or opening a webticket using the following link: https://www.adtran.com/openacase