A/C freeze ups

[oceanworker]

I just converted my r-12 system to r-134 w/ new accumulator, compressor (clutch was shot), and rubber hoses, etc. It is sure cold but every 15 minutes the evaporator core freezes up and it hardly blows any cool air thru the vents. After a while it seems to thaw out and is good and cool again.
I read from previous posts that it may be the clutch pressure switch on the accumulator causing the compressor not to cycle off when the evaporator gets too cold.
Am I on the right track? Thanks in advance to anyone smarter than me.

 

[yob_yeknom]

Don't have an answer, sorry.

The same thing is happening to a friend's Acura Integra and she wants me to fix it, but I don't know where to start. It will actually begin to blow frost from the vents right before it freezes up.

Any ideas?

 

[TDG]

I think you are on the right track with the clutch cycling swith. Does the AC system cycle on and off or does it just keep on running?

You should be able to purchase an AC pressure gauge at most auto parts stores, hook it up to the low side and watch the pressure while on max AC with the blower running at full speed. The AC system should cycle off when the pressure drops to 25 psi and cycle back on when it comes up to about 44 psi.

Or you could just save your cash and buy a new clutch cycling swith.

 

[Robb]

Does the blower blow fine before it freezes? All outlets open and blowing a good amount? Frozen coils are a sign of not enough air being moved across it.

Robb

 

[oceanworker]

Yes. The blower runs good until the evaporator freezes up. then I think all the frost and ice on it restricts the flow. After about 10 minutes it seems to "thaw out" and the blower blows good again.
I was told by someone that this problem can be caused by a bad pressure switch not allowing the compressor to cycle off when the evaporator starts to freeze, but ford tells me that when the ambient (outside) temperature is higher than 90 degrees, the compressor wont cycle off.
Any ideas?

 

[Robb]

I'm not sure on the 90 degree thing. That would be the same as saying that when it is 90 degrees outside, your house a/c should never cut off (at least this would be true, if you were using max a/c in vehicle). If airflow is good, perhaps the refrigerant metering device (not sure which type Xs use) or sensing bulb may be shot.

Robb

 

[TDG]

Explorers use a fixed orifice tube system which what I think you are referring to by metering device. I didn't notice it mentioned but did you mess with the orifice tube at all while you were doing your conversion?

I think would be a good idea to go with the gauge setup so you can see what pressure the evaporator core is running at. The basic idea behind the clutch cycling switch is to control the evaporator core pressure at a point where the plate-fin surface of the evaporator temperature will be maintained slightly above freezing.

At high ambient or humidity levels the AC compressor may never shut off, but at the same time the evaporator core pressure should never drop to the point where it starts to freeze.

 

[SWLathrop]

Another thing to check for is the thermostat for the evaporator. I had the one on my 88 Ranger go south on me. Ford wanted $45. I just took it out of the system. Ended up with the exact problem described. Thermostat cuts the compressor out to avoid evaporator feeze-up.

 

[tac0meat]

i get this same problem too, my a/c blows hard and cold (at highway speeds) but after a little while will freeze up and still blow very cold but not much airflow, i have found that by turnning the compressor off but leavin the blower goin it will thaw out and i just engage the compressor when the air starts to warm up, it will then be good to go for an hour or so

 

[Matthewacuna85]

Has anyone figured this issue yet? My Ex acts like it's freezing up on the highway, the fan still blows but hardly comes out of the vents. The rear a/c still blows and it's cold. It's only in the highway, been told it's not moving enough air, could it be the fan clutch? Thanks for the input!