A/C behavior

[Pillarian]

I recently filled the A/C, perhaps too much. It now makes a "barking/hissing" noise periodically when engaged. Did I over do it? Oh by the way, the A/C barely blows cool air whereas it blew quite cold air. If I overfilled it, how do I relieve the overfill?

Thanks

 

[Rob94]

Two words: Pressure gauge. You need to know what the pressure is. Without those numbers, we can't even begin to guess how much refrigerant you have in the system.

 

[Pillarian]

Give me a range of values to look for before I get to the pressure gauge. Thank you much.

 

[SHOhhhhMan!]

High side and low side pressure should both be about ambient temp. So if it's 85 degrees out and the car hasn't been running recently, both should read about 85psi. Now, obviously if the car was run recently, the engine bay will be warmer than ambient temp.

High side pressure with the A/C running should be ambient temp x2, plus the humidity, plus or minus 20. So, say it's 70 degrees with 30% humidity. 70 x 2 = 140. 140 + 30 = 170. So high side pressure should be 150-190 psi.

Your low side should cycle from 20psi to 40psi every now and then with the A/C running. The ideal vent temp your should be getting is about 38*F.

 

[rangerj]

Adding refrigerant to a system that is not getting as cold as we would like is a common mistake. The system could be full and have all of the internal components working properly. The radiator fan may be malfunctioning, or the thermister switch in the evaporator core could be the problem. Then there is the low pressure switch, or the high pressure switch.

The point to the above is that, as stated above, the key to diagnosing A/C problems is the pressures in the low pressure side of the system, and the high pressure side of the system. Too much refrigerant can increase the high pressures so that the pressure reliefe valve lets off some pressure. That may be the noises you are hearing.

There are no magic numbers. The pressures are directly related to the ambient temperature surrounding the system, ie the under the hood temperature. This is affected by the cooling fan, or the motion of the vehicle AND the atmospheric temperature.

The automobile A/C system should be able to produce a 40 degree to 50 degree difference in the A/C air temperature (coming out of the center vent) and the outside air temperature.

So, as stated above, you need to determine the pressures in your system before anything else can be done to correct your A/C problem, that is the problem you tried to solve by adding refrigerant.

I think you can rent or borrow a set of gauges from Auto Zone for a deposit. Gauge sets are R-134a or R-12 specific. rangerj