My AC keeps burning transformers in the past 6-9 months. I had a
RiteTemp 8022 thermostat before, and it worked fine for AC, but burnt
transformer whenever switched to Heat. The primary of the transformer
was burned out everytime. The transformer is 220V input for the 24V
output.

Later I found I had wrong thermostat and also bad wiring to the
thermostat. I install a new expensive transformer (about $40 vs $10
for the regular one) with pop-up switch (sorry, I don't know the exact
name. It's kind of transformer with a reset switch giving certain
protection) and replaced the thermostat by RiteTemp 8010 with wiring
instruction from the RiteTemp support. Both AC and Heat worked well
for about 3 months. Now, the transformer is bad again. However, both
the primary and secondary seem fine, but the reset switch of the
transformer went bad.

The possible reasons I can think a
1) The tenent turn on/off the thermostat too often (This is for the
rent house).
2) The tenent set the temperature too low for Cool and too high for
Heat, so that the AC/Heat hard gets rest.
3) The AC/Heat unit is two old. It is about 10 years old.

Do you have any idea what is the problem?
How can I find the problem and correct it?

Following is the wiring for the RiteTemp 8010 as you
taught me:

(Left are terminals from AC unit, right are terminals on RiteTemp 8010)
R to RH with Jumper to RC
O to O
G to G
Y to Y with jumper to the W terminal
W to W2
B to C
Others are not used.

Thanks for help.

Scott