skullyyy

Hello I have a 92 300sl and recently changed the head gasket which had its ups and downs hahaha but after words I got it done and the car runs good but when I now put on the heater it blows cold air/slight warmer room temp air and makes the engine run rough any ideas maybe I did something wrong during the head gasket or forgot something but so far no leaks of coolant or oil or strange noises just curious as any info will help thank you