Slagathor

I have not driven my 4 Runner much over the last 4-5 years. I just got a new job...and the old company car is gone... I am back to using my old faithful 98 4Runner. It has 180K miles...but aside from paint scratches...is in great shape...

Except....

The A/C runs for about 1-2 hours...then stops cooling. The fan still runs...it just starts pumping out warm air. While it cools...it is very cold. The hotter it is outside, the less time it takes for the A/C to stop cooling. It it is over 100 Deg F...it only works for about 30 minutes before it stops cooling.

We had an A/C tech/mechanic check the system. It is fully charged, and no leaks at all.

I am thinking it must be a switch or relay that shorts out in higher temperature situations (thermal expansion?) If it were an actual functional component (as opposed to a control component), then the A/C would not work at all. As it is...it works great...then the refrigeration loop stops working. That has to be a control / switch / electronics issue...

Some possible causes:
1. Pressure switch. This is right above the exhaust header...in the hottest part of the engine compartment. My neighbor has a 2000 6 Cly...and it has the same A/C components. He said his Pressure Switch went bad.
2. A/C Amplified - This is what the A/C suggested we change.
3. Expansion valve - This was another suggestion by the AC tech...but this does not make sense. If this were bad...wouldn't it work poorly all the time?

Any advice on where to start?

Thanks in advance!

bicklebok

I have very limited knowledge of a/c's, but the symptom you described happened to me on another vehicle years ago. It was an orifice that becomes blocked when the a/c runs for a while. Where it's at, I couldnt tell you. Wish I could be of more help.

tunnelmotor99

Are you sure the compressor is running? If the pressure switch was bad the compressor clutch wouldn't engage. Also check the evaporator drain to see if it's clogged or otherwise not draining properly. I have seen evaporator cases fill up with water which freezes and entombs the core in ice, thus allowing no airflow across the evaporator.

DailyDrive

Not where, but when. And the when is when the A/C stops working. Begin with checking if the a/c compressor is engaged when the A/C "is not cooling".

87 'runner boosted

In my few years of working on semi's and their a/c systems (which they are all basically the same), the symptom your experiencing sounds like the system may be freezing up. When it does stop working, pop your hood and check where the lines go through the firewall, see if they are iced up at all...on trucks, I have seen ice building up to 3/4" thick around the lines. Also, as stated above by tunnelmotor, the evaporator being clogged can cause this issue, as can the orifice tube being blocked up. I dont know if you have access to recovery machines or not (as it is illegal to open an a/c system to the atmosphere, not saying you cant do it, just that its illegal), but the orifice tube will be where two lines meet and there should be about a 4" straight section of line where they connect that houses the orifice tube. Its just a little filtering device that helps contain debris in the case of an internal compressor failure that shoots metal pieces throughout system.

offset442

water in the system, you live somewhere very humid? and open the lines or replace components with out using a vacuum pump and a new dryer/filter can?

water forms crystal after the expansion valve that slowly build up and restrict the flow shutting down the compressor via the high side pressure switch, when the ice melts the pressure equalizes and it would cool again........?

jumper(short) the low side pressure switch and test repete with the high side pressure switch if it has one, if for awhile if the air flows fine you have th problem, there is also a thermal disc type switch attached to the line some where to cut out the compressor when the evaporator starts to get too cold, its function is to prevent icing of the evaporator, could be that guy thats bad, (can only bend so many times be fore failure) probably buried in the dash catacomb somewhere near or attached to the evap coil, could find its wires and short them to test it............good luck................