QuestionMy AC works fine but at an idle and driving at slow speeds it continuously pulls allot of power from the motor. The way it happens is very jerky and doesn't feel right. Is that what happens when it needs to be refilled?
AnswerThere is the possibility that it is cycling on and off too much due to low refrigerant but you may have another problem such as an excessively high, high side pressure, defective IAC valve or compressor problem. It can certainly be felt if the system is over charged.
It is imperative that the cooling fan operates sufficiently at low speeds to help irradiate the eat away from from the condenser. If the heat does not leave the pressure goes up proportionally and the compressor will need more engine power to overcome this.
Also, another thing to look at is the IAC valve. The IAC valve commands a regulated vacuum leak past the throttle body to increase engine RPM when there is a power steering or AC compressor command into the computer.
A low system charge will make the compressor cycle very frequently but not necessarily rob the engine of power. If the system is low on charge then the compressor will not be making very high high side pressures therefore not using excessive engine power.
It might not hurt to have a tech look at the clutch cooling fan mechanism and the IAC valve. These can both be culprits.
I do have to say it is very important to verify refrigerant level before attempting advanced diagnostics. Low refrigerant is the most common AC complaint and causes the strangest of problems.
Wayne
