Problems calculating checksum for AirConditioner

I am trying to reverse engineer an AC Indoor unit <-> thermostat communication. So far I've succeeded in parsing the bits and bytes.

I discovered that the upper and lower nibbles need to be reversed to get consecutive values for temperature values, for example, so I assume that part is correct.

Also, the unit sends the payload twice, so I assume the values are correct.

Finally, I am trying to calculate the checksum of the received values, but I cannot find a pattern that results in a matching checksum.

I did notice that value change of 0x01 raises the checksum by 0x10, so I tried reversing each value and sum them up, but that did not provide the expected result. On the other hand, changing 0x10 to 0x30 does not affect the checksum at all.

Here some of the received bytes (received twice like this):

vent hex: 09 da d1 04 01 00 44 13 a4 09 00 40 10 04 01 1d cool hex: 09 d8 d1 04 01 00 40 17 a4 09 00 40 10 04 01 6a ai hex: 09 de d1 04 01 01 40 17 a4 09 00 40 10 04 01 7c dehumhex: 09 dc d1 04 01 00 40 15 24 09 00 40 10 04 01 5a heat hex: 09 d9 d1 04 01 01 40 17 a4 f1 00 40 10 04 01 4c hex: 2a d7 10 04 01 00 40 10 04 01 00 48 14 7c 09 78 1=0001 hex: 2a d7 30 04 01 00 40 10 04 01 00 48 14 7c 09 78 3=0011 hex: 2a d7 50 04 01 00 40 10 04 01 00 48 14 7c 09 79 5=0101 hex: 2a d7 70 04 01 00 40 10 04 01 00 48 14 7c 09 79 7=0111 hex: 2a d7 90 04 01 00 40 10 04 01 00 48 14 7c 09 7a 9=1001 hex: 2a d7 b0 04 01 00 40 10 04 01 00 48 14 7c 09 7a B=1011 hex: 2a d7 d0 04 01 00 40 10 04 01 00 48 14 7c 09 7b D=1101 hex: 2a d7 f0 04 01 00 40 10 04 01 00 48 14 7c 09 7b F=1111 hex: 2a d6 10 04 01 00 40 10 04 01 00 48 14 7c 09 7c hex: 2a d6 30 04 01 00 40 10 04 01 00 48 14 7c 09 7c hex: 2a d6 70 04 01 00 40 10 04 01 00 48 14 7c 09 7d hex: 2a d6 50 04 01 00 40 10 04 01 00 48 14 7c 09 7d hex: 2a d6 b0 04 01 00 40 10 04 01 00 48 14 7c 09 7e hex: 2a d6 d0 04 01 00 40 10 04 01 00 48 14 7c 09 7f hex: 2a d6 f0 04 01 00 40 10 04 01 00 48 14 7c 09 7f 

Here is some parsed output of a temperature decrease with the reversed payload(rhex):

source: 09 head 110 mode 38 modeb 11001 fan 0 bfan: 000 unkownb: 1000 swing: 4 bswing 00000100 plasma 1 tempStart: 0001 temp: 90 tempStop: 010 airclean 1 unkown: 01 01 44 splayload: e9 rest: 00 40 10 04 01 chksum: 2a hex: 09 d9 11 04 01 01 44 15 a5 e9 00 40 10 04 01 2a rhex 90 9b 88 20 80 80 22 a8 a5 97 00 02 08 20 80 54 source: 09 head 110 mode 38 modeb 11001 fan 0 bfan: 000 unkownb: 1000 swing: 4 bswing 00000100 plasma 1 tempStart: 0001 temp: 88 tempStop: 010 airclean 1 unkown: 01 01 44 splayload: e9 rest: 00 40 10 04 01 chksum: 6a hex: 09 d9 11 04 01 01 44 11 a5 e9 00 40 10 04 01 6a rhex 90 9b 88 20 80 80 22 88 a5 97 00 02 08 20 80 56 

Maybe somebody can give me a hint in the right direction.

The test setup is running in Python on a Raspberry Pi.