Passenger side floorboard wet? Try this!

My 1995 RM Wagon recently contracted the "my passenger side floorboard is sopping wet" disease. Water was leaking down from behind the evaporator cover, right against the firewall. I removed the evaporator cover 3 times trying to get it sealed up. No dice. It was not leaking in from the cowl during rainstorms. It was not due to the elbow being absent on the drain tube. Gremlins were not sneaking in and dumping their bathwater on my carpet(although that's the way it smelled).

Turns out my AC refrigerant levels were low - like only half full. It was running so cold that it made a BUNCH of water. The whole bottom of the evap cover was sweaty it was so cold.

I always thought the AC would blow warm air if levels were low - but my half-full AC system was frosty, arctically cold. Never would have known the freon was low.

Just something else to check, thought I'd post this in case it might help someone in the future. Good luck!

Thanks Doug and I am sure that others will chime in,this is going to be interesting!Never heard of this happening before but anything is possible!

Is there any fluid draining from the drain tube when this event takes place? Make sure the evaporator drain is clear.

Put a set of gauges on this thing and let us know what the low side readings are, sounds like the low pressure cycling switch is not doing it job, especially if the system is frosting.

where is the evaporator drain? I never see any water coming out of my car and now it's started to smell kinda bad.

Drain is right under the heater core connections on the firewall (in the engine compartment). There should be a 90 degree elbow on there pointing at the ground. I have two cars currently without engines, so if you need a pic, LMK!

first check that the drain elbow is still there. If not Advanced Auto sells a PVC elbow that works as a replacement. Without this piece the water drains out of the evaporator and back in & along the firewall.

How was it determined that the charge quantity was low? Was it evacuated and weighed? If so, then ignore this post. But, if you just looked at the low side pressure gauge then read on...

The charge cannot be accurately determined by pressure. The system is designed to shut off the compressor when the low pressure side is drawn down to approximately 23psi (assuming R-134a). The pressure and the temperature are directly related, so pressures below 23 psi cause the temperature to be below freezing -- causing the frost that you saw building up on the accumulator as the condensation freezes and also where you can't see: around the evaporator fins. If allowed to stay cold enough, the evaporator fins would eventually clog with frost, and air couldn't pass through. The compressor restarts when the pressure rises to 40 psi. At that point, any developing frost has warmed back to condensation and can drip off the evaporator to either the drain or your carpet. Note that the accumulator has no fins, nor a fan blowing warm air directly over it's surface, so it may retain a thin layer of frost.

As gmtech already intimated, The pressure will drop below 23 psi if the low pressure cycling switch is not adjusted properly. To adjust, unplug the connector from the switch to reveal a slot-head screw. Clockwise raises the pressure. Use tiny increments -- 1/16 of a turn at a time. Plug it back in and verify the pressure between each adjustment.

It is certainly possible to add more refrigerant, to the point that the compressor cannot draw the low side below 23 psi, but that is overcharging the system. Overcharging will reduce the efficiency of the system, as it prevents complete vapourization of the refrigerant. So it certainly will keep the evaporator from getting as cold. However, preventing complete vapourization of the refrigerant is very risky: the compressor is only designed to pump vapour. If liquid is sucked into the compressor (known as "liquid slugging") the compressor can be irreparably damaged.

If you are interested in learning more, I wrote a long thread about auto AC, tailored to the B-body systems. Basic principles of Auto AC