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Your next "worry" is that the freeze switch isn't opening the compressor circuit. new, they should open just above freezing, close again before the temp gets above about 40ºF at the probe. The freeze switch is in fact a wearing part, based on the beryllium-copper diaphragm that actuates a little microswitch. The diaphragm is part of a little bellows, and metal work-hardens with flexing over time. It becomes less and less responsive until it finally sticks closed. Many folks with tired systems don't have the refrigeration-side performance needed to get the evaporator that cold, so never get to experience the "worry" over an evaporator freeze-up. You'll know it's happening as airflow falls off. Just turn the compressor off manually and let it thaw out. Best to have a functioning freeze switch especially in more humid conditions -- it will ice faster with the humidity, and will also dump cold water on your feet as it thaws. There's no guarantee that the bottom will thaw before the top, so the path to the drain hose may not be clear.
It's up to about 90 out now. I didn't go for as long of a drive, just up the road 2 miles to the post office with a couple redlights on the way and it was still getting to 40f at the vents.
Hopefully in 100 degrees as long as it's not sitting in traffic for extended periods of time, it'll keep working. But at least now, as long as that pressure switch (mercedes # 124 820 83 10 behr # 6ZL 351 022-011) works, at least the worst case scenario should be the ac just turns off rather than the compressor safety blow out.
I was thinking about the freeze switch not working now. I have a feeling that once it's warmer here it won't be getting down to 25 again anyway, but I'll look into getting a replacement freeze switch. At least it doesn't require opening the a/c system though.
I didn't check to see if I had water dripping from the drain. I didn't hear water sloshing around in the dash, so hopefully it is, but I do want to check to make sure it's clear.
I tested and confirmed that all the actuators for the flaps are holding vacuum and it sounds like they're all moving in the dash. When I turn on the AC I can hear what I assume is the recirc flap moving and pulling air from in the cabin vs from outside.
Hi Matt,
I seem to remember that the freeze switch is adjustable. You may be able to pull it out and put it in ice water, then turn a screw to change the set point. I could be wrong, or the freeze switch may simply be broken.
Good luck,
Dave
I tested and confirmed that all the actuators for the flaps are holding vacuum and it sounds like they're all moving in the dash. When I turn on the AC I can hear what I assume is the recirc flap moving and pulling air from in the cabin vs from outside.
Cool, dont be worried about the freeze switch just yet.
Driving 2 miles on a 90d day wont get the system cool inlet air to judge what the outlet really can be.
Need to measure the system inlet air temp at the floor.
It got down even further last night after 30 miles on the highway with it being about 75 ambient. Surprisingly I still had plenty of airflow on fan speed 2.
Hi Matt,
I seem to remember that the freeze switch is adjustable. You may be able to pull it out and put it in ice water, then turn a screw to change the set point. I could be wrong, or the freeze switch may simply be broken.
Good luck,
Dave
The freeze switch is in fact adjustable as Dave explains. With the cover removed (a couple screws...) and switch out of the car, there's a tiny adjustment on the microswitch position that you can adjust. The probe goes into ice water, with an accurate thermometer that has numbers you can actually read. My digital AC thermometer works, or if you have a good instant-read grilling thermometer that will work too. Use your DMM set to read Ohms/continuity at the terminals, then probe in a glass, a little water in the glass, then ice in the glass. Watch the temperature fall on the thermometer, and see where the switch opens. Should be around 35ºF (falling). Adjust if needed. Take some ice out and slowly add more water, so you can see the switch close before the temperature gets above 40ºF (rising).
As mentioned previously, the little bellows will get work-hardened where it flexes as it cycles normally. The operating range slowly expands when that happens, to a point where there isn't motion available there to cycle the switch correctly. Time for a new switch then. This is a common fatigue failure, FWIW. The switches are pretty reasonable, and the only replacement caveats are to avoid puncturing an evaporator tube when you place the probe, and avoid kinking the capillary tube. Else replacement is a whole lot faster than the testing. I've dinked with a few of these switches, and all needed replacement.
Great results, Matt. The evaporator might not ice up, if the humidity is low engough, but a properly functioning freeze switch is good protection and easy to swap.
Good luck,
Dave
Normally it is pretty humid here, but it mustn't be this week. I'll add a new freeze switch to my list of things to replace. I tried bumping the temp slider up to 70-75 last night and that didn't seem to change the temp of the air coming out to reach the new temp target, despite it being about 65 in the car at that point. So I might have some more hvac work to do still, but at least I can survive driving it around here in the summer now.
When I read about the freeze switch adjustment it brought to mind an issue I have. Air is good but after driving a while especially on the interstate I can feel a rise in temperature and a musty smell. It corrects itself after a few minutes could this be a candidate for adjustment or just cutting out the compressor and doing as designed?
Depends on the temperature but.... If it's doing that ll by itself, it's working as designed. Do the test/adjust with the ice water if the temp range you measure differs from the limits I shared. The pocket digital kitchen thermometer I use stores min and max, making the testing a snap.
I didn't pull the freeze switch off my blue car yet, but I did pull the one off my parts car. I found that the bellows on it doesn't move with temp at all (even when put in the freezer). It seems to be stuck fully extended. I'll have to pull the one off the car and see what it looks like, but I bet it's the same and just needs replaced.
Hey guys, I really enjoyed reading all of the threads about Captian OCDs AC problems! Working with HVAC of many different types and applications for about 45 years I thought everyone's comments and advise was very specific and on point! I would only add one thing. I read that you did clean and pressure washed the condenser and straightened a few fins, Excellent! Take it one step further. Soak it with a cleaner such as purple power or spray nine on the condenser, front and back (as much as possible) it wont hurt the radiator to get cleaned also and let it sit for a few minutes, then rinse thoroughly. The film from 30 plus years does insulate the metal (too much paint will also insulate the condenser). You should see a difference.
Its the same for all AC. The first 6 inches at the bottom of you home AC condenser is practically worthless because it suffers from insufficient air flow... from STUFF the air, which collects dirt, grass, leaves, etc all which slow down the air movement and cooling your refrigerant.
06-01-2019, 01:11 PM
