dryer cut off if vent hose is connected to dryer

We have similar problem. We use the dryer vent cleaning apparatus with the drill and there is no clog. But it will cut off if vent hose is connected to dryer. If I don’t have it connected. It will dry a load of clothes. We did have a dryer repair man come out to replace the heating coil. It’s snapped right away when he turned it on .He took it away and brought it back. We didn’t have this drying problem before he did this repair. If I don’t have it connected. It will dry a load of clothes. We did have a dryer repair man come out to replace the heating coil. It’s snapped right away when he turned it on the first time. That meant he had it touching the metal. I am wondering if he blew some type of fuse And just used the same coil without replacing it? I just can’t understand why it won’t work when not vented. It is only 9 feet long for the vent hose. Unless we get an answer I’ll have to buy a new dryer and see if this solves the problem. So confused!