Hello All:

The evaporator on my '92 245 is icing up on highway drives. It seems that after about 40 minutes or so of 60mph driving, the air flow and cooling start to diminish.

If I set it from recirc to fresh and turn the AC off it will thaw gradually and you can feel the air start to flow more freely at the vents.

I had a leak in the high pressure line repaired this summer and had the system converted from the original R12 to 134a (R12 is no longer legal in Ontario).

Is evaporator freezing the result of an undercharge?


--
Herb Goltz, London, Ontario, Canada '92 245 w/109K mi

Herb, My evaporator iced up after a long highway drive also. I think with so much air flowing through the condenser at highway speed and the control button on (rec) the system become to efficient and ices up. I now set the control button to (fresh) on the highway and (rec) in town. And I have not had any more problems.
--
Bruce S. near D.C.

It could be undercharged. An undercharge gets the evaporator vapor pressure
down to where it cools less efficiently but to a colder temp. Hook up your
gauges and see what the low pressure equivalent temp is. It should NOT be
below about 34°F/2°C. You may be able to keep it from icing by always
running the fan on high, but you have to do that as soon as you turn the
AC on.
--
George Downs, Bartlesville, Oklahoma, Central US

Hi Herb,

Nice to see your evap can actually get that cold! :)

Yah I would check that the drain is not clogged and the evap housing filling with water. Basically at idle on a humid day (not many left now) run it for a few minutes and then look under the car, water should be running down around the center of the firewall area. If not water with cold blowing A/C, drain is clogged, common problem. Easy to unclog the tube from underneat, it fills with road crud.

Your 'dial' on the dash is a thermostat. It has a probe that goes into the evaporator. It is possible the person who last worked there did not install the proble correctly. Without it, it would think the evap is always cold and never cycle off the compressor clutch. Evap freezing in this mode is completely normal, it's like the dial is in the red zone. See owners manual, it explains that.

I woud make sure the probe is curretly installed in the side of tyhe evaporator (passenger side) and the thermostat switch (in the dash works as expected. ... maybe he even broke the probe.

A low charge would make is less cooling efficient, not colder. 93- 240s do not work like this, very different with the pressure sensor on the accumulator triguring the compr clutch.

Take care!
Greg Mustang
greg_mustang@hotmail.com
Montreal - Ottawa

I think the probe should be attached to the evaporator outlet pipe. This will allow the AC control system to cycle the compressor and ensure that the evaporator never ices up.
Cabbie2169

Correction: third paragrah:

"... always cold..." should be "... always warm..."

Sorry :)

Greg

Either low charge or accumulated water in the evaporator housing. Make sure the drain tube is clear and condensation is running out when the A/C is on.

My 93 245 does the same thing. Although this wasn't my problem, check your clutch cycling switch on the accumulator, by attaching a gauge to the low pressure side. Check the FAQ for the exact pressure (low 20s, I've forgotten exact pressure) at which the clutch should shut off. If too low, then the evaporator could freeze up. My 93 doesn't have an adjustable switch, but your 92 should, since it came with R12. You could try adjusting the switch to have the clutch shut off at a slightly higher pressure, but the trade off is less cooling.

The other possibility is that the system doesn't have the correct charge. The R134a systems are much more sensitive to this and the only way to really know the correct charge is to evacuate the system and refill by weight. That's why the newer 134a cars only have a low side - so gauges are not used for determining the correct charge.

BTW, did you install an adjustable VOV when you switched over?

If this isn't the problem and you find out what is, pls post it.