Evaporator froze up again.

[mthomas58]

Drove from Atlanta to Hilton Head today in 85 degree ambient temps (humidity high). Vent temps rose and airfow declined one hour into the trip (classic freeze up symptoms). Turned A/C off and opened up the windows for about 45 minutes, then turned fan on high and temp setting to lowest setting. All seemed well although compressor never shut off (even at lowest temp setting). Evap apparently iced up again....this time I did not notice a reduction in airflow BUT, after refueling in HH upon arrival (15-20min stop) upon start-up, ice shot out the center vents!

OK, to my point. Evap is orig and has recently been cleaned along with evap box. Thinking I need to upgrade to a modern serpentine evap unit to reduce freeze ups. If i do this, I will add a ProCooler "while im in there".

Seems like the condenser fans I've added have helped get my vent temps down but my old technology evap cannot handle it.

Make sense?

[Hugh R]

What vent temps are you getting? If around 32 you'll freeze the evaporator. On the back of the temperature control there is a little set screw you can turn to make the thermostat turn on or off at higher or lower temps. I think you screw in for higher temps, could be wrong.

[mthomas58]

I can get initial vent tems below 32 (obviously not sustainable) and I have to back off the temp control. One of my problems may be that I do not have the probe properly inseted into to evap coil....it is laying on top of the evap, therefore, not shutting off the compressor when it should. I really need to open up the evap box and fix this.

Is a higher efficiency evap coil less prone to freeze ups vs an OEM?

[patkeefe]

Either low on refrigerant, or not enough airflow over the evaporator. Those are the two most certain causes of icing.

[ipacketeer]

First of all check your connections on the A/C system and make sure there are no leaks. You can spot sometimes oil collecting dirt that is sign a of leak. You can not do much with the Evaporator unless it is leaking and needs repair or replacement. listen to what Pat said and check to see that your high and low side pressures are correct. they tell you all about the state of the refrigerant charge. If you set your evaporator fan on high it may help (this is not a solution), also it may make the cabin too cold for you.

[mthomas58]

Originally posted by patkeefe
Either low on refrigerant, or not enough airflow over the evaporator. Those are the two most certain causes of icing.

Well, I do not have barrier hoses (two replaced last year with OEM's and one orig 20 yr old hose remains) so low on R12 is certainly a possibility. I'll check and ask the tech to give me the high and low side readings (not that I understand what they mean - but I'm eager to learn).

Thanks!

[patkeefe]

Mark:
You should be in the neighborhood of 35-40 PSI low (suction) pressure, and around 160 PSI high side. This depends on cabin temp and ambient temp. Also assumes R-12 as the working fluid. Sounds like you can get away cheap on this one, and not need to completely overhaul your system.

FWIW, cars are the worst leakers of refrigerant ever. Historically, they all leak eventually.

Pat

[1982911SCTarga]

One of my problems may be that I do not have the probe properly inseted into to evap coil....it is laying on top of the evap, thereforem not shutting off the compressor when it should.

Just a wild guess here, but I think this fact might be important in the overall scheme of things.

Brian

[wilke3169]

"One of my problems may be that I do not have the probe properly inseted into to evap coil....it is laying on top of the evap, thereforem not shutting off the compressor when it should. I really need to open up teh evap box and fix this."
That is the problem I bet. The sensor if not properly installed is allowing the compressor to run continuously, dropping the coil temp below freezing. I would make that my first priority and I think your problem will be fixed.

[Jim727]

Originally posted by mthomas58
One of my problems may be that I do not have the probe properly inseted into to evap coil....it is laying on top of the evap, thereforem not shutting off the compressor when it should. I really need to open up teh evap box and fix this.

That was my first thought on reading your post. The probe slips into a brass receptacle tube which is inserted through the top of the evaporator box into the evaporator core. My understanding is that the receptacle tube should be positioned so that it contacts the cooling fins but not the refrigerant tubes if it is to correctly modulate the temps. The situation you describe would have the temp probe always sensing a warm temperature and would attempt to drive the system continuously colder.

Also, suggest you replace the old hoses with barrier hoses. Not that expensive and a huge improvement.

[mthomas58]

No brass tube in the evap coil to insert temp probe. I'll have to order a new one from our host.

[1982911SCTarga]

You could fabricate your own outer tube -- hobby shops carry thin brass tubes of various sizes. The outer tube is there to protect the probe/bulb from chafing and wear (I think) and is about 4 inches long. The end that should go about halfway into your evaporator core is crimped shut and cut at a 45-degree angle to help when it's inserted.

Another option is to post a wanted notice in the for-sale section. Likely someone's got one of those protective tubes laying around from an AC delete or repair job.

How come whoever did your evap cleaning didn't put the thermostatic control probe where it belongs?

Brian

[Barrpete]

Originally posted by mthomas58
No brass tube in the evap coil to insert temp probe. I'll have to order a new one from our host.

Or you could just take some copper tubing, crimp one end and flare the other. That's what I did when I kinked the original removing it. Just had to file the crimped end to fit into the hole in the box.

[1974carrera]

You can make the brass tube if you want. I'm installing a new serpentine evaporator and found that the brass tube in the original evaporator, was cracked. I used a beveled punch to flare the end of a ~ 5" piece of new brass tube, pinched the other end and cut to the length I needed...works perfect. In the pics below you can see the original tube is about 4 3/4" +/- long (the new one I made is a little shorter because of the way it needs to fit in the serpentine evaporator).

another thought...it could be that the flare collapsed or cracked on the end of your brass tube, allowing it to slide down into the evaporator housing.

[mthomas58]

Question on the proper method of installing the copper guide tube:

Does the guide tube get inserted into the evap cover hole after the box is closed up or does it go in before closing it up?

If the latter, the guide tube (planning on following the suggestions here and fabricating by own) would need to be shorter and the box cover would be even more difficulty to close up than it already is.

Thanks!

[1982911SCTarga]

After you close it up, or before (test fit) if you're worried about finding the location. With the evap cover and blower off, you should be able to see where the probe cover goes in (the fin's will show a sort of hole). It's a little tricky. Don't just slam the protective tube in there. On mine it went in at an angle, too.

Brian

[Jim727]

When I did mine, the evaporator box was out of the car - makes it much easier. In the car you can practice for a new career as a contortionist.

I replaced my evaporator with a Griffiths evaporator (beautiful piece!) so with the evaporator box cover off I made sure the fragile heat-transfer fins were unbent. I then put the cover back on and eased the receiver tube in until it contacted the heat-transfer fins and pressed gently to create a small dent. Removed the cover again and used a thin awl to prep the channel for the receiver tube at the location of the dent I just created, making sure the channel did not contact the primary cooling tubes. Next, cover back on and clipped closed. I noted the alignment of the crimp at the end of the receiver tube since it needs to be inserted parallel to the heat-transfer fins, not perpendicular to them or it will hang up, and dropped the receiver tube in. Properly aligned and the channel prepped, the receiver tube needed only a gentle push to slide into its final position. It isn't difficult, just requires being a bit meticulous.

If you do remove the evaporator box cover, remember that you need to reseal the opening where the expansion valve and tubing exit.

[mthomas58]

Jim727, this is exactly what I was looking for. Many thanks!
Mark

[Jim727]

My pleasure. Let us know how it goes.

[mthomas58]

OK, probe is now properly inserted in evap coil and tomorrow at lunch I'm getting a R-12 recharge. If that doesn't solve the evap freeze-up problem, my new tech suggests replacing the 20 yr old expansion valve.

Wish me luck....dog days of summer are just around the corner!