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Did you short the low pressure switch when you added refrigerant? It's the only way I can get enough into a flat system and draw the enough refrigerant in to allow the clutch to engage.
R-134 or R-12? So the whole system is 36 psig if the compressor has not run. If ambient temperature is 70 degrees F. The static (saturation) pressure should be about 70 psig for both R-12 and R-134A. At 90 degrees F ambient temp the pressures should read about 100 psig if you have some liquid refrigerant in the system. I agree with ykf7b0 that you need to bypass the low pressure switch or find a way to get enough refrigerant in the system to allow the low pressure switch to reset so it can cycle to allow charging more refrigerant.
I just spent an hour with the speed control wiring diagram. The switch only operates on high speed and the heater control does not change where the air is coming from - always from the heater under the dash.
I am getting 12v to the resistor which is new, for all speeds so the speed selector switch seems to be sending power. I think it might be the heater control selector switch ?
St. Jude Donor '05-'06,'11,'13-'14,'16,'18,'19,'24, '25
If you have 12 volts on the 3 different wires (while changing fan speed) going to the resister pack then the issue will be in the wiring between the resister pack and the blower motor relay. The voltage should be lower coming out of the resister pack for each coil (resistance wire) going to the blower relay. Try the blower relay to start and see if the wires from the resister pack are sending voltage there then from there to the blower motor.
If you only have 36 psi chances are you don't have enough pressure to reset the low pressure switch.
Neal
Last edited by chevymans 77; Jul 4, 2020 at 11:33 AM.
Do you own a set of auto a/c gauges? If yes, use them. If no, add refrigerant until the pressure is high enough to cycle the ac compressor on and off without jumping the low pressure switch.
When running pressure is about 100 psi and when turned off it drops to 0-5 psi. This is with the Low pressure switch jumpered out.
Doesn't seem right at all, and backwards. Static pressure as mentioned in post three depending on air temp should be lot higher. Zero pressure is empty system when static and low or going into a vacuum when running. Places like autozone lend equipment out such as AC gauges, leak tester, vacuum pumps, etc.
Picture of your gauge being used?