error code "dr" on frigidaire elec dryer

Dryer Repair
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1

My dryer works only in low heat mode but when attempting to start in any other mode (med. high) choice it gives the error code "dr". I thought it was the little door button because when i played with it I could get it to work for a load or 2. I replaced this button and it worked for one week. At the same time I also tightened the connections. So now, a week later I am back in the same boat and can’t get it to start at in except in the low heat mode. Getting the error code "dr" which is not even listed in my manual. Appreciate any ideas and suggestions. thank you