It has fittings for a standard R-134a guage set. Low side is up high on the drivers' fenderwell, just in front of the forward firewall. High side is down near the front of the compressor, near the condenser and fan belt. Can't really get them wrong, as high and low side are different...

As a quick and dirty test you can try jumpering the low pressure switch on the dryer. If the compressor starts, it is an indication the system is too low on refrigerant to operate. If forget which one of the two switches on the dryer is the low pressure switch. But if the electric fans on the condensor start up when you test it; then it's the other one...

- JimY