My ac compressor has seized up and now needs to be replace at a cost of nearly 2,000. Maybe I can go a few weeks with out it, but I will not be able to have heat or defrost as the colder temps come in for the fall. does anyone know why this would happen? 109K on the odometer. The mechanic also suggested that I change the timing belt and the water pump (neither are broken) replacing these is also expensive. am I crazy for not changing the timing belt and water pump?
You will still have heat and defrost even without the A/C. The timing belt is due and might as well do the water pump.
“My ac compressor has seized up . . .”
I take it to mean it failed catastrophically, shooting debris into the AC system . . . unless I hear otherwise
In that case, you’ll need:
AC compressor, complete with clutch installed and pre-gapped
receiver-drier
flush the AC system
install a suction filter, so that the new AC compressor doesn’t suck in remaining debris
It’s also possible you need a new condenser. It’s now always possible . . . or advisable . . . to flush a condenser
Anything that rotates and has a bearing will eventually fail. That’s just the way of mechanical things. On a 2009 w/100K, it seems a little early. But not entirely out of line. The worker who built it might have been wanted to get a head start on a 3 day holiday and skipped some of the final adjustments and just sent it to the shipping department maybe. Who knows.
Certain things can make the bearing wear out faster, so ask your mechanic to double check the belt is the right tension, the pulley is the correct one for the application, and the other pulley’s that this belt goes around are in the same geometrical plane. There’s a special laser-guided pulley alignment gadget mechanics sometimes use to do this.
I assume the mechanic suggested the timing belt/water pump change-out b/c he knows is time for that based on the age of the car and the miles driven, and has nothing to do with the problem w/the AC compressor. It’s a pretty common thing to replace the water pump when replacing the timing belt, because it usually makes the most economic sense. But whether it makes sense or not for you depends on the way your Subaru is designed. If the mechanic would have to do most of the same work just to replace the water pump at some future date when it fails (see first sentence), that is when it makes the most economic sense to replace the water pump along with the timing belt.
I assume you’ve already unplugged the AC compressor so it doesn’t try to come on in “defrost.”
If your A/C compressor is seized or broken internally I can see that the compressor, condenser, drier, and expansion valve will need to be replaced. In addition flushing all the lines and evaporator will be required. I can see this getting to the $1500 or more range.
You should be able to have the A/C system disabled so you can use your heater or defrost this winter.
As for why it happened, well, the car has 109,000 miles on it. Moving parts fail. It happens.
And yes, according to Subaru your car is due for the routine scheduled maintenance timing belt service.
Others have posted the correct repair procedures so I will only address your question about why it happened. It could be one of several reasons.
One is that the A/C system never had the correct amount of oil to begin with and it was a dead man walking.
Two is that a refrigerant leak developed and oil was lost along with the leak. This is quite normal with age on any A/C system and more than likely the case here.
It’s also my non-scientific opinion that this could be more prevalent nowadays due to compressors being mounted down low. Many leaks are at the compressor shaft seal. The system is under high pressure even when it’s not in operation so you have the constant forcing of refrigerant oil out by the pressurized refrigerant. The down low mounting also means oil pooling down low which only exacerbates the problem.
In the old days most compressors were mounted up high in the engine compartment so while seals and clutch bearing failures would occur catastrophic compressor failures were not as big an issue unless the car had a ton of miles and age on it. Just my 2 cents… 
Everyone here has given good advice, but one thing should be stressed.
Your engine has a timing belt VS a timing chain. A chain will normally last the life of the engine. but a timing belt is normally only good for just over 100,000 miles and you’ve passed that.
If your engine is an interference engine and the belt breaks it could cost you the entire engine.
Much more than the cost to have the belt changed.
This doesn’t have to be done right today, but the longer you put it off the greater the chances that the belt will break and cause major damage.
Because winter is on it’s way…I’d opt for having the mechanic unplug the AC for now, change the timing belt and water pump soon, and comeback in late winter/early spring for the AC repair.
You’ll still have heat and defrosters!!!
Yosemite
Thanks for the opinions and advice. I didn’t think I could still have heat and defrost without replacing the AC unit. If this can be done be unplugging the AC, I will ask the mechanic to do it.
If you can locate the AC compressor, you just have to unplug the electrical to it.
you can look up the replacement part on-line (AC compressor) at NAPA/ Autozone etc, and you can get a picture of what you need to search for. It will run off the belts on the front of the motor.
Yosemite
You’ll have heat and defrost air, but the moisture will not be removed from the air. Defrost automatically uses the AC to remove the moisture from the air. Also, using defrost mode you should select the “Fresh” air setting not recirculated air.