Freon is required to be recovered with a machine into in approved container. Realistically you have a system that may only hold 3oz of freon. You will lose that hooking up the gauges. Freon always has a smell. Be careful it can be addicting 
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Good news is it has a tap. If this is the case it will not be tough to pressure it up and charge it. There are several ways to go about this. Here is what I would do. Put a gauge on the tap. Generally if there is only one tap it is on the low pressure side. Start the unit with the gauge hooked up. When the compressor starts the pressure should drop. It may even go in a vacuum. If this happens you know your compressor is working. Lets assume your compressor is working for now. Turn the unit off and let the pressure on the gauge build back up. I would check all connections and copper joints with a spray bottle filled with soap and water. On such a small system it wouldn't take much of a loss to cause problems. If you find a leak determine if it can be fixed. Once this is done "recover" the R134a using all proper equipment following the laws of your state
Once there is no additional freon in the Engel hook it up to a vacuum pump. Let it run for 30 minutes or so. Weigh in the correct amount of R134a. You can probably do this while the system is in a vacuum without it running. Don't forget your gauges hold a little freon so you may need to add a slight bit extra. Once this is done start the unit. Be sure to replace your cap on the freon line and leak check.
If the compressor is not working electrical troubleshooting will be in order. Before you tear into the freon system make sure if there is a fan motor near the compressor it is running and the condenser fins are clear.
. Good news is it has a tap. If this is the case it will not be tough to pressure it up and charge it. There are several ways to go about this. Here is what I would do. Put a gauge on the tap. Generally if there is only one tap it is on the low pressure side. Start the unit with the gauge hooked up. When the compressor starts the pressure should drop. It may even go in a vacuum. If this happens you know your compressor is working. Lets assume your compressor is working for now. Turn the unit off and let the pressure on the gauge build back up. I would check all connections and copper joints with a spray bottle filled with soap and water. On such a small system it wouldn't take much of a loss to cause problems. If you find a leak determine if it can be fixed. Once this is done "recover" the R134a using all proper equipment following the laws of your state
Once there is no additional freon in the Engel hook it up to a vacuum pump. Let it run for 30 minutes or so. Weigh in the correct amount of R134a. You can probably do this while the system is in a vacuum without it running. Don't forget your gauges hold a little freon so you may need to add a slight bit extra. Once this is done start the unit. Be sure to replace your cap on the freon line and leak check. If the compressor is not working electrical troubleshooting will be in order. Before you tear into the freon system make sure if there is a fan motor near the compressor it is running and the condenser fins are clear.
