when I use the defrost my engines rpms will power down is this the ait conditioning unti/compresser or possibly belt? this happened only after i had the spark plugs changed . have 87,000 miles on thius car
If the AC compressor is seized up, keeping the AC and defrost off, or removing the belt to the compressor, will prevent this until you can get it fixed.
The engine is supposed to compensate for the drag of the AC compressor. If it isn’t the idle control valve could be bad. You could also simply have a vacuum leak; whoever replaced the plugs could have knocked a vacuum line loose.