Why does my car shake and drive like its weighed down when the AC is on?

I've got a 2001 Honda Accord 4cyl. I got it a year ago at 196k miles and it now has 198k miles and it's been well maintained in the past and we've kept it pretty well maintained but the AC makes the car shake no matter what, and when it's driving with it on, it doesn't accelerate as fast. My dad said its just stealing horsepower but I don't think my car should shake like it does. I don't want to spend the money to get a mechanic to look at it just yet and either way my parents don't believe me so I came to the Internet for help.

Somebody could have overcharged the A/C system (a DIY'er) causing too much pressure in the system requiring a lot of horsepower from the engine. Take it to an A/C shop for a check up.

John's right people think more is better when it's not and can cause just what your experiencing.

Aircon can add quite a load to the engine, so your dad is correct, it is parasitic on engine power.

Usually, the cause is not the aircon but is usually due to a badly maintained engine coping badly with the additional load, but if the engine is well maintained at regular intervals then it's worth looking at the aircon again; the pump pulley is belt driven and runs all the time the engine is running, but is freewheeling when the aircon is turned off. Turning it on causes a clutch to engage so that the pulley operates the aircon pump; if the pump is the original unit then it's highly likely that the clutch mechanism is badly worn and not able to drive the pump consistently.

If the car works flawlessly under all conditions except when the aircon is turned on then that confirms the diagnosis.

So you have two choices: get the aircon repaired (potentially very expensive) or remove the fuse to the aircon and disable it as the erratic load isn't good for the engine. If the car is otherwise excellent and you live somewhere that aircon is vital then you might decide that it's worth getting it repaired; if you're lucky it may be just the solenoid which operates the clutch or the clutch itself might be separately replaceable from the aircon pump. I'd suggest that it's at least worth taking the car to an aircon specialist to get a diagnosis and you can then decide what to do.

In the very front of the engine compartment is a special radiator that's connected to the A/C system. This is the condenser, and if air can't flow easily thru it then condensation won't occur properly which drives up high-side pressure and that impedes compressor rotation, in turn impeding engine rotation. Check to see if debris is plugging the fins where air passes. Don't be afraid to hose out any dirt, bugs, leaves out with a hose. Also, while spraying it with water, have someone inside the car with it running to see if the air cools down.

Make sure the condenser fan is working when the A/C is on. This is the large front engine fan on the driver's side. If not spinning, you could look at the fuse, or test it by running 12V directly to the connector on the fan assembly to see if it works at all (black to black, red to red…). They are cheap on eBay just make sure it's broke before ordering a new/used one. If you rule these out, then you are looking at an expensive trip to the mechanic.

Like others say, the AC system itself could be fine, but shaking under AC load could indicate a number of engine problems - ask your auto parts store about tuning up the engine.