I have just completed replacing all of the A/C lines, cleaning of the evaporator, and replacing compressor seal on my 86 Carrera. Now my evaporator is icing up after less then an hour of use. Hopw do I know this besides the smell when I shut the car off and restart a few minutes later I have to turn the a/c off and on a couple of times to get it to work. Any ideas on how to prevent this short of not using it?

Thanks

Ken

 

Sounds like your system is low on refrigerant.

Kirk

82SC

 

Just had it charged up also. Is my problem indictative of low coolant?
When the system is working it blows very cold air.

 

Cleaning of the evaporator......

Early systems used a capillary tube and/or bulb (looks like a simple but thick wire) to "sense" the temperature of the airflow from, around, and at the surface of the evaporator. If enough of the tube or bulb is not close enough to the evaporator surface the compressor will cycle too often and the condensed moisture will freeze.

 

I have the capillary tube. After cleaning the evap and reinstalling it I had a problem with placement of the tube in the box. I tried (doing it blind) to get it to cover most of the evap only to have it contact the fan while running.
I removed and reinserted it down through or along side the evap.
What is and how do you get the proper placement of the tube?

 

First, remove the capilary tube along with the atatched A/C switch and put in a freezer to confirm that the switch, in full cool position, will still open at sub-freezing levels. Very common failure is this assembly.

 

The capilary tube should not go along the side of the evaporator. It should go into a protective tube that goes down inside of the evap. If you break the capilary tube the gas inside will come out making it useless.

 

There is no protective tube in the evap box. No signs of one either.

 

Maybe someone who has access to PET right now can ck to make sure that is applicable to your year model. I've never seen one without it. It's not easy to install. You always feel like you're going to break something. You have to get it all the way in and it can't hit the evap tubes head on or it will stop early.

 

What is PET? The hole where I inserted the tube is located on the top of the box. I believe I got it down the side of the box. I am sure it is touching part of the evap though.

 

PET is the parts disc from porsche. It's illeagle to have a copy so I'm sure no one here has one. The tube goes almost straight down into the evap. towards the back of the car slightly. if you just shove the tube in without the tube inserted 1st I doubt it will make it all the way. Also you have to ck the specs. My manuals are at work. Their is a spec on how deep the tube is supposed to be.

 

Thanks

 

Ksarver, you're temperature switch may be working to good. If you have the temperature switch turned to max cooling, try running it at a higher temp setting. This allows the icing to dissipate and then you can find the right position, somewhere between the two. It's happened to me on two different cars. May not be your problem, but try it.

 

Ken,

If you want to test the function of your thermostat you don't need to remove the entire unit (pita). You can simply remove the aluminum sensing tube from the evaporator coil, do not bend it sharply or break the sealed aluminum tube because it contains refrigerant gas which contracts and expands with the temperature of the evaporator; turning the compressor on and off.

Assuming there no other issues with the AC circuits; if all other parts of the circuits such as fuses, relays, wire connections, etc. are working). Air temperature where you are working should be above 60F.

Remove the sensing tube from evaporator. Prepare a tall glass filled with chopped ice and salt. Set aside your Scotch or Bourbon for later. Source a digital thermometer and insert in the glass; this we quite helpful to tell you the temperature the thermostat is seeing; naturally dependent upon the accuracy of the digital thermometer.

With your battery fully charged, with ign key on in the accessory position, turn on RH AC fan speed switch.

With the sensing tube out of the evaporator, turn LH thermostat **** fully CW (right) to max cold position. The compressor clutch should engage and the front condenser blower motor should come on. If not, you can the thermostat is defective.

Slowly turn the thermostat CCW (left) until the compressor clutch releases and front condenser blower motor turns off. If it does turn off you can assume that function in the thermostat switch is working. If the compressor and fan does not turn off when the thermostat switch is fully CCW to the off position then you can assume the thermostat is defective.

Insert the sensing tube down into the glass's ice mixture approximately 4 inches or so. Observe the digital thermometer's temperature, hopefully you will be near or below 33F or so. Turn the thermostat **** fully CW, the clutch and fan should turn off. If not you can assume thermostat is defective.

An alternative method to ice an water is a freeze aerosol used to test electronic circuits, certain aerosols that vapor off quickly (be careful of flammables) and refrigerant (watch out for the EPA and tree huggers).

In terms of a good working thermostat not doing its job: most common issue is the thermostat sensing tube is not make good contact with the cooling fins in the evaporator coil. This is because when tube is inserted in the coil the aluminum fins are near dead soft, no memory, they do not spring back and make good contact with the tube. This would require you to locate a position of fresh unbent fins adjacent to the area where the tube was originally located. Depending upon the year of your evaporator, pre 86 or 86 and onward, the locations and angle of insertion of the sensing tube are different. And, if you have an aftermarket evaporator coil, say a serpentine design, you will need to contact the supplier and ask them for the best location.

Feel free to PM if you need more help.

Thermostat Discussed here

 

The only thermostatic switch control failure I have experienced involved the electrical contacts being stuck closed, WELDED together, actually. Not saying the loss of refrigerant inside the tube isn't common, especially when work has been done in that area.

The compressor clutch is a fairly HIGH electrical load, INDUCTIVE load to boot. That inductive "kick" over thousands upon thousands of cycles will sometimes (often?) result in welding the contacts together.

Forcing the contacts open and filing them smooth again will get you going until you can get a replacement installed.