I have a 1994 g20 conversion van with front and rear ac. Since I bought it van the ac and air have not worked as they should.
The rear unit does not blow any air at all.
Check the ground for the rear fan. Often the aftermarket rear AC units don't drain properly and moisture will collect under the housing and corrode the ground for the fan. I had this happen on my 89 E150 with aftermarket rear air.
The front blow air on all fan speeds. Regardless of what air direction I set the controls to it will blow warm air to the windshield and footwell.
I am not familiar with Chevies, but on Dodges the dash vent doors that direct air to the various outlets are controlled by a vacuum modules and work via hoses and bellows that open and shut the flaps in the dash. I know older GM cars I have worked on also had the vacuum controlled HVAC system. I would start by looking at your control head for the AC. Is the vacuum line to the intake manifold hooked up? Is the control head unit working? Are all the hoses under the dash connected? Are the bellows that operate the vent doors working?
It has not blown cold air.
I tried a can of r134a, it would not go in, the gauge read in the red as overpressure.
Today I relieved some of the freon in the high valve. Now it will blow coldish air but everything is the same.
That is not how you go about charging your AC system. Overfiulling the system will cause it to go int bypass mode and not run the compressor. You need to get a set of manifold gauges for the AC system and look at both high and low side pressures. Also, the ambient temperature and humidity play important roles in system pressure. You should never put in more refrigerant than the system is designed for.
The high system pressure and poor cooling may also be due to a clogged filter in the receiver/dryer.
All things considered, unless you are willing to get the right tools, get a factory service manual, and learn how to repair the system correctly, you will be better off taking the van to a qualified AC service tech.
I just replaced the blower motor resistor as the old one was rusty. No change.
No change to.......what? The blower motor resistor in the dash only effects the front blower motor. if your fornt blower motor works fine, then a rusty ballast resistor will not impede blower performance.
Tomorrow I am going to replace the blower relay.
Again, why? If your front fan works, leave it alone. The rear fan operates independently of the front fan, does not have a resistor, and almost certainly does not have a relay.
What about the blend door?
See above. There are at least two- a hot/cold blend door and an output direction door that changes where the air comes out.
Blend doors are in the dash vent assembly, down by the heater core.
Also is there a rear blower motor and if so where is it?
Yes, it is in the rear AC unit housing.