I arrived for a non member no heat call. I first inspect the entry way package unit located on the rooftop. I found the far right and middle burners to have had a mud dobber nest built in the manifold not allowing the gas to pass through all wire the system to fire up and run. The gas wouldn’t ignite and trip the role out switches and shut the system down on safety lock out. I remove both nest from inside of the manifold set. I replaced the weak limit switch with the owners approval. I cucumber the system on and for no issues with the system at this time. I then replaced all filters per the owner request and i found a 12†duct to be sitting in a 14†return grill. This return duct is bringing in attic air and not filtering the air in the building. I brought this up to the owners and we decided to replace the grill with the proper size fittings.