A/C cold then gets warm

[JHZR2]

Hello,

my father's toyota and my mother's plymouth breeze have just both experienced the same AC issue, and so I would appreciate some advice.

The AC blows cold - very nice temperature, for a while... then, all of a sudden, the air becomes warm.

Now, on the toyota (dual AC system), we see ice on the evaporator on the rear unit, yet the low side pressure is not sufficiently low to freeze the evaporator (per my pro gauges, Im seeing that the center of the evaporator should be 38F).

We cant see the front evaporator on the toyota, or the evaporator on the breeze, but they both do the same thing.

Pressures start as such that from a static equilibrium reading, there is sufficient charge to have liquid refrigerant in the system - good sign. During operation, the pressures look OK, low side between 30-40 generally, with high pressure between 175 up to 225 or so as the car heats up and the condensor gets hot (spraying water on it does not help much).

Another thing that I note is that on the breeze, the silicone-filled anti flutter needles still flutter... something that I dont see on any of our other cars.

My take is that there is too much moisture in BOTH systems, such that on each system, the expansion valve freezes up. I didnt test the breeze, but on the toyota, wen the air stps blowing cold, the high pressure is normal, but low pressure is at zero or negative.

My suggestion has been to evacuate both systems, remove receiver/dryers on both, measure oil recovered, add same quantity of new oil to new receiver/dryers, close the systems back up, pull vacuum and then recharge.

Sound right? Sound accurate? Any other ideas? What about the flutter on the gages on the breeze???

Thanks in advance!!!

JMH

 

[Dominic]

How old are these vehicles? There is deisscant in the dryer and after so many years it will fail to remove excessive moisture. Also, the regulator for the compressor might not be functioning right causing it to kick off too soon.

 

[punisher]

You don't suddenly get moisture in an AC system. The dessicant is there to remove any residual moisture left in the system during its assembly and in the refrigerant charge. A fair amount of moisture can remain in a system even after a 30 minute vac no matter what the book says.

Main sign of moisture in a system- cools fine in the morning, once ambients get above 80-85F performance falls off, and higher than normal high side pressures. Systems with a sight glass on a dryer (high side) will show bubbles even when the charge is correct.

What is the ambient when your high side pressure is 225? Do the systems have an actual expansion valve, or is it an orifice tube (CCOT) system?

 

[JHZR2]

the toyota is a 94 and the plymouth is a 97. Ambient during testing is ~83F, though temperature near the condensor is surely higher after much operation, if tested with the car stationary... That is my problem too, since we are tersting with the car sitting in one spot, it is tough to gauge what exactly is "ambient" for right near the condensor, since it is obvious that the air in front of it is hotter than the air 10 feet away, so setting high side pressure is not trivial, for what I can see.

The explanation that it cools fine then tails off is exactly what we are seeing on these two cars.. Its funny too, because the toyota has been topped off at the dealer once or twice, but the plymouth has never been touched, and the cars are run year-round with AC on. Not a problem until just recently...

Any major work is for the pros to do... but now that I have a set of real gauges, and some interest in AC systems, I enjoy learning... thanks for your insight!

Thanks!

JMH