How do remove the pressure ,before you add r34 cooler

On your gauge,is "red" high pressure or low pressure?
If you are seeing a high pressure on your low side connected gauge and the compressor is not running,that is a "full charge" or better stabilized in the system.If your compressor is not "kicking in" you may have a defective electrical component in the A/C system.With the engine running,you can jump 12v power the the compressor clutch momentarily just to see if it is working.Don't leave it jumped to long as the system is designed to cycle with pressure from the low side pressure switch which is the next place to check and the compressor can also be jumped at the low side switch.
If your "red" is low or no pressure,then you have a leak and repairs to the system to stop the leak will have to be made.You can add 134a at this time with the engine running and A/C requested,and as pressure rises in the A/C system,the compressor should "kick in" and cold air should start flowing in your dash vents.45 degrees at the dash vent airflow temp usually equals a full charge.
DO NOT add any aftermarket "134a" that shows an EXPLOSIVE label on it.These are not 134a and are usually butane and/or propane mixes that you MAY NOT want spraying on you in a collision/any situation where the A/C system has become ruptured/compromised.

I looked at info for 1500--5.7L engine.
6 psi @ 1000 rpms
18 psi@2000 rpms
24 psi @ 4000 rpms

Sometimes, you can use analog gage in place of oil pressure sending unit and double check oil pressure that way. If oil pressure is actually low, if high mileage engine, I doubt replacing oil pump will help. I just wanted to add, check oil pressure engine warmed up.

if it is a 2000 nav it should not take freon it should be r34 you can buy this at your local walmart you add it to the upper cap in the engine compartment should be rite off the fire wall on that vehical i belive the passenger side

Hello! I believe you have an air bubble blocking the thermostat...Since you just changed it, the cooling system needs to be blead of trapped air...Start the engine with the radiator cap off, heat on high and let the engine run until all air has escaped...Slowly add 50/50 until all air is expelled and radiator is topped off...Replace the cap with a new one...Send a comment...Guru...saailer

I’m happy to help further over the phone at https://www.6ya.com/expert/david_6df67de3b14de867

The pressure on the low side it not very meaningful by itself.
What matters is the difference between the high and low.
The low normally can be up to 120 psi or so, and the high side can be twice that.
But when the AC is running, the low side should drop to less than when it is off.
But there could be lots of reasons for it not being very cold.
The pump clutch could be failing to engage. The release valve should be not opening. The air flaps could be letting heater air in instead of cold. The AC condenser fan fan or relay could be bad.
Etc.

May just need to be recharged, if r34 is too low, ac will not kick in, Wal-mart sells recharge kits and cans of r34 (insctructions are on kit)...expect to pay around $50 total if you do it yourself. If that doesn't work you may have to replace the AC compressor.

1. Drain anti_freeze low pressure air through the heater core will help empty it)
   
2. Disconnect Heater core hoses on the engine compartment side of the firewall.
3. Remove cover panel under dash.
4. Remove dash board brace (small support brace that runs from firewall to glove box shroud surround.)
5. Remove lower air box section. ( Many small screws so be sure you get them all)
6. Remove air conditioning evaporator (Some times this requires the disconnection of hoses in the engine compartment, But try to work around that first to avoid having to recharge your air conditioner.)
7. Remove the heater core mounting straps and screws.
8. Wiggle the heater core towards the glove box to extract the steel hoses from the firewall bushings/seals.
9. Be careful not to spill any remaining anti-freeze on the carpet.
10. If you had a leaky heater core be sure to clean the air box the best you can to keep the anti-freeze smell out of the car.
    
11. Reverse this procedure to install the new heater core.

I hope that helps someone in some way. It's not complicated but it is a pain in the rump to be upside down for that long. You may need to take several breaks during this process to give your neck and back a break as well as your knuckles... It's not an easy repair but it is pretty straight forward.

If I left any thing out please feel free to add comments to these instructions. Generally these instructions should cover most years of Buick Roadmasters.

Just an additional note:
If you have to disconnect your air you may have to upgrade your entire system to the new R34 system instead of R12 because of the new environmental laws in some areas. Try to avoid this as best you can because R34 is not as effective in an older systems as it is in newer systems simply because the evaporator and condenser are smaller and they need to be large to transfer the heat in the R34. It's not nearly as effective at the transfer of heat as the environmentally unfriendly R12 was.

Basic AC system consists of Compressor pump (on engine), Condenser (front grill with radiator) and Evaporator (Firewall). Pump has two ports output (high pressure) and return (low pressure). Follow lines from pump. High side is usually between pump and condenser. Follow lines and find second port this will be low side (refill) port. Paint or replace port caps (red high, blue low). Also, refrigerant in system determines port size (R12 or R34).

if pressure is in the red when engine is running and compressor is engaged, compressor clutch turning with pulley, and not getting cold air, it seems that your compressor may need to be changed. with engine running gage should read between 30 and 60 lbs.

what gage reads high? the red or the blue gage?