Air conditioner never seems to shut off
I think that your coils are frozen.
Ironically, I had the same issue with my HVAC system last week, although I am a few hundred miles south of you. Had an A/C man come out and he taught me about how units freeze up. Here are some things to check:

1) Are your air filters clean? Dirty air filters can suffocate the system and reduce the amount of efficiency. They could also cause the unit to freeze up (Which I will get to in a moment). If your system has been run without filters or with dirty filters for an extended period, the coils could also be very dirty and you will need a professional to clean them.

2) Is your thermostat set to a reasonable cool temperature? Do you have it on AUTO or ON? Sometimes leaving it set to "ON" 24/7 can be detrimental to your systems health.

3) Would you say that your vents feel under-powered? If so, this may be another sign of the coils freezing.

4) Is your A/C Drain line free? The drain line is a small 3/4" PVC pipe that comes out of your unit and drains outside. If it gets clogged, then the natural condensation that your A/C unit generates can't be drained, and could cause the system to operate incorrectly. You can try vacuuming it with a wet/dry vac. It will let out somewhere outside your home, which is where you want to connect the vacuum. Don't use a regular household vacuum!
On my unit (See picture below) there is a T joint and a cleanout, so I didn't have to cut my line. I was able to pour water through it with a funnel to verify that it was not clogged.




Touch the insulated refrigerant line. You should see it uncovered right next to the indoor unit). It should be very cool to the touch. If it is only slightly cool after several minutes of running the outdoor unit, then you are probably low on refrigerant.
Is the air sufficiently cooled? Get a thermometer and measure the temperature of the air as close to the unit as you can. In my case there is an intake a few feet from it, so I measured the temp in the duct. Then, measure the temperature in a outgoing vent. The difference should be about 20 degrees (F). If it's less (it was about 11 for me), then you may not have enough refrigerant in your lines.


So here is something to try:
Turn OFF your A/C, and run the fan only. So turn your thermostat to OFF and the fan to ON (not auto). This will help defrost the coils. After about 4 hours, cut on the air again. Does the air feel significantly cooler and at a better air flow rate? This may indicate that the coils did in fact freeze.



When your coils freeze, it reduces airflow. The outside unit keeps pumping cold refrigerant through the system, thus making the problem worse. Sometimes the ice will make the air feel very humid, but because only a small amount of air can go through, the house will not cool.

It's okay if your coils freeze up once in a blue moon, (once or twice a year). But, if you are having to defrost every day like I was, then you need to call a repairman. You likely have a refrigerant leak. This is nothing to panic over - it's not like Carbon Monoxide or anything, but, it means that your system is burning electricity like no tomorrow ($$$) and you are still cooking in your own castle.

The repairman will assess if you have a leak and what your pressure is and should be at. He will refill your lines (and replace them if he needs to). While the bill will be high, I ended up saving $200 a month on my power bill after he came out (House went from 4000kwh to 1200kwh).

Note: Don't try to recharge the A/C refrigerant with an OTC kit, there are multiple kinds of refrigerant, and you should never mix them. A professional can properly assess what kind of refrigerant you need, if there is a leak, and what your options are to fix it.

Good Luck!