Where is the low side service port for A C - 1999 Pontiac Montana

Verify ambient temperature is above 65 degrees F.

1. Safety> - safety glasses, long sleeves and gloves, (exposure to refrigerant can cause frostbite).

2. Attach hoses to manifold> assembly, (hi, lo, and fill).

3. Remove caps from service ports, (Low press. Larger tube from evaporator to accumulator - passenger side over fender well; High Pressure - smaller tube from evaporator along firewall towards driver's side). Verify service> ports are clean.

4. Attach low press. and high press hoses to proper service ports.

5. Start car>, reset low refrig code, and turn ac on high and fan on high.

6. Read gauges and compare with chart provided with gauge set.

7. If low and high press readings are both low, then system needs recharge.

8. To recharge, attach fill hose to can of R134a and slowly open low press valve>, (NOT HIGH PRESS VALVE), until low press side reads 40 psi.

9. When flow stops and pressures stabilize close valves> and disconnect manifold from service ports and refrigerant can. Replace service port caps.

The low side port is in the low side line from the AC compressor, this is the larger of the two lines from the compressor. The charging hose will not hook up to the wrong port as they are completely different.

The R134A connection hose will only fit on the low side service port. The high side port is bigger and will not fit that hose.

The low pressure port on the 2003 grand am is actually behind the engine, near the firewall on the passenger side. Good luck getting your hose down there though, I ended up buying an extension hose.

the low side on this year is on the larger lines of the two sizes,it will be the 1/4 in service port,the larger of the two ports the small service port is on the small line ,it is the high side ,,but that is for r12 system which it came out with,if it has been retofitted to 134a freon use it will have a different kind of service port the large line will have the smaller of the two ports it is the low side ,looks like a quick connect,,,,if it hasnt been changed over ,go to parts store and ask for service port retrofit for 134s low side ,if u do not have gauges dont get the high side service port,,,if so ask for 3/16 size high side retofit .

Should be reciever/drier pass side undehood.will be fitting with black cap their.Attach to port with charge line .Must have engine running and compressor on.

2002 is what I have. should be similar

Service Gauge Port Valves
The high-pressure service gauge port valve is located on the A/C receiver drier manifold and tube assembly.
The low pressure service gauge port valve is located on the manifold of the A/C compressor manifold and tube assembly at the A/C compressor.

Item Part Number Description 1 19860 A/C evaporator core 2 19849 Thermostatic expansion valve 3 19A834 Manifold and tube assembly—thermostatic expansion valve 4 19D850 Manifold and tube assembly—A/C compressor 5 19E762 A/C charge port valve (low side) 6 19E762 A/C pressure relief valve 7 19703 A/C compressor 8 19D594 A/C pressure transducer 9 19712 A/C condenser core 10 19D701 A/C charge port valve (high side) 11 19N585 Manifold and tube assembly—receiver drier 12 19959 Receiver drier 13 19C734 Sensor—evaporator air discharge temperature

Your service port will always be in the larger line of the two .. which is low pressure side. It might be in the dryer also which is low side.. your dryer is about 3 inches across and 8 inches long and also has your pressure switch for the AC compressor in it.. holler if you dont find it now... thanks Jerry

The Low side is always the thicker/ bigger aluminum line.