A/c not workin, it was about 50 degrees out side a/c low pressure only has about 20 psi, car inside only cools down to about 67 degrees, , put a can of 134a in it up the pressure on low side did not get colder, so let pressure back off , whats wrong
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try to throw cool water on the condencer front of the engine radiator and see whether any cool air comes in the car. If so see whether the pressure valve is working okey or not because might the pressure is not sufficient.
speed up engine with air on and see if compressor turns off. if it does then it is low pressure. if it has electric radiator fans they should be on when the ac is on. if they dont work then it will make the pressure higher
It all depends on the outside (ambient) air temperature. Your A/C low pressure switch is designed to turn the compressor off at 24 Psi. and turn it back on at 45 Psi. Most systems will normally run at between 25 and 40 Psi when the system is running on HIGH blower and "MAX" or "RECIRCULATE". A system that is fully charged may run at 25 Psi when the ambient temperature is 75 Deg. (F) and may run at 40 Psi when the ambient temperature is at 90 Deg. (F). (it can be even higher if ambient temperatures are higher than 90 Degrees.)
To properly diagnose a malfunctioning A/C system, the HIGH side pressure must also be checked. Restrictions in the system can make the low side pressure look normal while the high side pressure is high enough to blow hoses apart. (400+ Psi.)
These numbers are a little high depsite the high ambient conditions.Amazingly enough ,automotive low side suction pressure will equal the degrees its putting out at the evaporator coil...for instance,70 psi low side pressure will produce about 70 degrees of cooling. At 300 psi on the high side(which is high) this is about as low as the suction pressure will go....you need it to go lower.I would probably be concerned with the freon level as a slight overcharge could boost these numbers.Poor air flow through the condenser can also create a higher head pressure than desired.If possible,I would evacuate and re-charge the system with the correct amount of 134a refrigerant. Try to get those pressures lower...about 250/50 would be a decent pressure value in this ambient condition.Verify good airflow through the coils and pay close attention to any foreign debris like plastic grocery bags or wrappers covering the coils...Ive even seen these make their way between the small gap between the condenser and radiator so use a light and inspect carefully for this.Air flow through that condenser coil is vital and any deficit there will create high head pressure which obviously causes high suction pressures....good luck