Is there a relay for the air suspension compressor on my car.

Congratulations you have air suspension! Most likely you have a leak somewhere which is why people convert older cars to standard suspension.

I checked for leaks, but found none. any other suggestions.

Check for leaks until you find it.

I’d check the the sensors....there are 2 for the front and one for the rear. My rear went out it actually wasn’t the sensor. It was the small adjustment rod on the sensor that rusted and fell off. $75 bucks from dealer. Like $260 for sensor with rod. Hope it helps. Look up ride height sensors.