85 A/C temp sensor?

heidi85ho · Posted: Sun May 29, 2016 12:23 pm Post subject: 85 A/C temp sensor?

Wondering if anyone has experienced failure of the evaporator temperature sensor in the a/c system?
The sender in my 85 seems to have failed. Bypassing the sender allows the a/c to run. When operating, both low and high pressures are normal and cooling is sufficient. The resistance reading on the sender hits 6,000 ohms on a 1k scale, so I think it history.
Big questions are availability and removal.
From searching I can't find the specific part, but I think I have seen one for a bmw that I could make work.
Removal looks to be a bear, so I was wondering about running with it bypassed.
Thoughts?
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85 westy-1.9-standard trans, FAS GenV 2.0

dhaavers · Posted: Sun May 29, 2016 5:53 pm Post subject: Re: 85 a/c ?

IIRC there was a thread on this exact topic just a week or two ago...???

Not sure where exactly, but it sounds familiar. Sorry not more help... Embarassed

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86 White Wolfsburg Westy Weekender
"The WonderVan"
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dobryan · Posted: Sun May 29, 2016 5:59 pm Post subject: Re: 85 a/c ?

Seems to me syncrojael did something like this with a bypass switch.... not sure though....
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Howesight · Posted: Sun May 29, 2016 6:00 pm Post subject: Re: 85 a/c ?

The 1985 units were oddballs. Can you post a pic of your AC temp and fan dash switch to help identify?
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'86 Syncro Westy SVX

heidi85ho · Posted: Mon May 30, 2016 3:58 am Post subject: Re: 85 a/c ?

My searches came up with a good parts and wiring diagram posted by Westified in 2015. But unfortunately there are no part numbers.
And Cellardoors post of his total a/c rehab was fabulous.

Only one post, by turbo2cv, indicating trouble with the controller, bypassed the evaporator temp sensor as a work around for the controller.

No posts that I have found deal with actually replacing a failed evap temp sensor. Since they are usually inserted into the fins of the evap coil, I wonder if sticking one into the mesh in the front of the coil wold be ok. Or just leaving it bypassed, as turbo2cv has done.

Howesight, here pix of my fan/temp controller and also the temp sensor connection in the evap coil area. And also the parts and wiring diagram I found.
The part being #24.

Also, as a note, the two gray wires connecting the temp sensor show a slight melt point in the insulation. I have checked carefully and there is no shorting going on. The insulation is still complete.

Image may have been reduced in size. Click image to view fullscreen.

[/img]
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85 westy-1.9-standard trans, FAS GenV 2.0

dhaavers · Posted: Mon May 30, 2016 5:19 am Post subject: Re: 85 a/c ?

heidi85ho · Posted: Mon May 30, 2016 6:01 am Post subject: Re: 85 a/c ?

Wish it were that simple!
In my first post I said I bypassed the sensor. Unplugging and jumping it was how I bypassed. So I temporarily reattached for the photo.
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85 westy-1.9-standard trans, FAS GenV 2.0

heidi85ho · Posted: Mon May 30, 2016 7:52 am Post subject: Re: 85 a/c ?

Dave....dobryan

Thanks for the pointer. I searched syncro jaels posts and found reference to the temp sensor and its bypass on page 48 of his red tek conversion post.
Good info. Great memory on your part!
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85 westy-1.9-standard trans, FAS GenV 2.0

Farf · Posted: Mon May 30, 2016 11:43 am Post subject: Re: 85 a/c ?

A reading of 6000 on the K Ohm scale definitely sounds like a bad thermistor. I went ahead and checked my thermistor (easily accessed and removed) and measured the resistance when I placed it in the freezer:

At 0 degrees F (-17.8 C) - 39.4 K Ohms

At Room temp of 71 degrees F (21.7 C) - 5.54 K Ohms

It appears that the thermistor is probably a 5K NTC thermistor, see chart below.

http://mcshaneinc.com/html/TS141_Specs.html#CurveTable

You can probably get one for a few bucks and make your own replacement abandoning your existing one in place or get motivated and solder in a new thermistor in place of the old. My thermistor is accessed from the rear where it is inserted into the coil behind the grille. I don't think running the a/c without freeze protection is a good long term solution.

Good luck, Mike

kamzcab86 · Posted: Mon May 30, 2016 12:05 pm Post subject: Re: 85 a/c?

heidi85ho · Posted: Mon May 30, 2016 1:01 pm Post subject: Re: 85 A/C temp sensor?

Farf
Thanks for the input. Your plan of abandoning the current one is my thinking also. Since mine is inserted from the top, I plan to just leave it and insert one thru the back of the evaporator. The specs were what I needed.

Kam
Thanks for the part number. I did end up finding it a JimEllis Vw in Atlanta, but like you said...NLA
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85 westy-1.9-standard trans, FAS GenV 2.0

Farf · Posted: Mon May 30, 2016 4:53 pm Post subject: Re: 85 A/C temp sensor?

Just for clarification, when you measured the resistance on the K Ohm scale did you actually read 6000.00 or 6.0? If you read 6.0 your evap. sensor may not be bad and the problem could be with your dash thermostat or the inter-connecting wires.

Mike

heidi85ho · Posted: Tue May 31, 2016 7:50 am Post subject: Re: 85 A/C temp sensor?

Farf
I have an inexpensive sears analog meter.
It has one resistance scale....labeled X1k
When checking the temp sensor, ambient temp 85f, a/c off, the needle rests at 6 on the very top scale pictured below
With the sensor bypassed the dash mounted on/off thermostat switch works fine, turning the compressor on and off with rotation of the thermostat rotary dial.

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85 westy-1.9-standard trans, FAS GenV 2.0

Farf · Posted: Tue May 31, 2016 8:51 am Post subject: Re: 85 A/C temp sensor?

Ah, you got me by doing the math for me. So, 6000 Ohms @ 85F. If the chart I attached in the earlier post is actually correct, I would think you would see around 4100 Ohms @ 85F. Not sure if thats enough difference to keep your a/c from operating. Anyway, thermistors are cheap and easy to get, so hopefully that will take care of your problem. As a side note, I checked the resistance of the thermostat control on the dash from the point where the evap. sensor plugs in.

At 76F:
Max Cool: 49.8 K Ohms
Warmest Setting: 268.5 K Ohms

Somewhere in all of this, the various resistances conspire to send a millivolt signal to the solid state control in the dash, maybe I'll figure it out someday.

Good luck,
Mike

heidi85ho · Posted: Tue May 31, 2016 4:46 pm Post subject: Re: 85 A/C temp sensor?

Farf
Out of curiosity, since your temp sensor enters the coil from the back, what does it look like?
Is it the metal probe style? If so, how long is it?
I have found this one on Amazon of all places, but am concerned it may be to long.
http://www.amazon.com/ACM-C-Evaporator-Temperature...ure+sensor
Thanks
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85 westy-1.9-standard trans, FAS GenV 2.0

Farf · Posted: Tue May 31, 2016 6:58 pm Post subject: Re: 85 A/C temp sensor?

No metel sheath or probe, its exactly like yours, just stuck into the coil about an inch or so. The sensor end looks like the attached image below with some heat shrink on it. I'm out of town tonight will snap pic tomorrow.

Mike

http://www.mouser.com/Search/m_ProductDetail.aspx?...fgodw18JNQ

Farf · Posted: Wed Jun 01, 2016 4:40 pm Post subject: Re: 85 A/C temp sensor?

The red end contains the thermister and it looks like it was dipped in some plastic goop similar to a tool handle. The plug end is quite common, I've seen them at the hardware store. I think if you can find a 5000 ohm @ 25C NTC thermister you could make your own.
Once again, don't know if it will work but the above mentioned thermister temp/resistance chart corresponds fairly well with my sensor.

Mike


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