Last year I had a Lennox XP15 heat pump installed along with a CBX27 air handler (with heating parts). I live in Montreal and the temperature can get really cold during the winter. At one point it was -9F and the heat pump was still working. I was told that usually a heat pump stops working around 5 F so I was getting worried. I called my installer and he told me not to worry, that the system would switch automatically to the furnace when the temperature would get too cold. Well, after a few days of cold temperature, the heap pump stopped working but then when the temperature got warmer, the heat pump wouldn't start up again. I called my tech guy and after a few weeks of waiting, he finally showed up and to make a long story short, he had to replace 2 parts (one being the motor part), and install a thermostat outside (in the heat pump). He basically blamed Lennox for the failure but I'm 99% sure it's because the heap pump kept running in really cold weather.

He installed a thermostat, A19AGC-77 from Johnson Controls:

The are 2 pdf files with some information. He told me that he set up the thermostat so that when the temperature goes below 5F, the heap pump stops.

But something is still wrong and it looks like he inversed the wiring because instead of having the heap pump stop working when it's too cold, the heap pump stops working when it's too hot, which is what happened when the temperature went up to 10F recently.

When I explained the problem he told me that it's probably a faulty thermostat. He's supposed to come back in a few days to take a look. Meanwhile I manually calibrated the dial and pointer to 60F so my heap pump doesn't stop working in cold weather. If it gets below -9F, I still have the option to switch to emergency heat from my inside thermostat, a White-Rodgers.

I've attached a few pictures I took of the outside thermostat. I hope someone can tell me if there is an error in his wiring. There are 3 connectors below the temperature indicator, from top to bottom they are Yellow, Blue and Red. It looks like the connections he made are as followed:

[Yellow wire] to [Red connector]
[Black wire] to [Blue connector]
[Purple and White wire] to [Yellow connector]

Can someone tell me what is wrong with that ? My gut feeling is that it's bad wiring.

More info on the thermostat is available in the pdf files

Thanks in advance !