Jump to content

Need an AC sensor ID'd......


Murphy

Recommended Posts

Since I had my AC system converted to R134 it's been sooo nice, but we have a small problem and determined it to be a faulty sensor on top of the firewall housing. I beleive this sensor shutsdown the compressor in case of a freeze-up situation......ANyway, I have a picture of it here. The intermitent problem was that the compressor would shutdown from time to time for no apparrent reason. Touching/tapping the wires on this sensor would cause the compressor to kick in again. We've wired around it for now.....

ACsensors_zpsd2780054.jpg

Link to comment
Share on other sites

I believe the part you’re asking about is the ambient temperature switch. It functions when the control is set to bi-level. It prevents the compressor from operating when the air temperature is below 37 degrees F. This protects the evaporator from freezing up and stopping the air flow and thus burning up the fan motor.

It's connected to the thermal fuse at the "B" pin.

Link to comment
Share on other sites

I have two part numbers for that part. The first one covers 1971~1975 "ALL Passenger" P/N 7934224. The next one is P/N 3917359. Either one will work. You can find them in junk yards for a buck or two. If you have to have a new one be prepared to pay for it. They go for about $100.00 plus on Ebay. IE:

 

link

Link to comment
Share on other sites

Murphy,

 

If you wish to test yours before you spend your cash, do this:

 

1. Take it out by removing the two screws.

2. Test to see if the switch is closed with a continuity tester. You should have a complete circuit.

3. Put it in the freezer for about 10 minutes.

4. Remove it from the freezer and run the same continuity test. It should show an open circuit.

5. Wait a few minutes and listen for the switch to click.

6. Run the continuity test again you should have a closed circuit again. If these tests all pass the switch is good.

Link to comment
Share on other sites

Thanks Joe, Oddly enough, I see 2 parts, Part #3917359 and #3971359. The correct number is 3917359, the sellers on ebay have typoed this several times.........I'm going to test as you mentioned. Thanks again. In my photo above, what is the other electrical connection at the front of the evaporator box?

 

Several sellers mention in their description "with auto-temperature control" What does that really mean?

I also see numbers 483326 & 9343146.....

Link to comment
Share on other sites

Murph,

 

I also noticed the Ebay sellers were using a transposed number in their advertisements. They're just not reading the boxes correctly I believe.

 

The other device shown in your picture is the blower resister. In short, what it does, is provide the resistance needed to reduce the fan blower speed for the lower settings on the dash switch. Each setting routes the power through one of the resistor coils causing the fan to run at a reduced speed. On a 4 speed switch, like the ones used in an A/C car, the high position on the switch is the only one that runs direct to the fan motor. It’s mounted in the evaporator box so air flows across it to prevent it from over heating.

 

The other part numbers you asked about are not in my parts book. My book only covers Chevrolet part numbers from 1960 to 1975. These parts may be from a different car line IE: Buick or Oldsmobile etc. or from later years after 1975.

 

As far as I know, for the ambient switch there were two basic designs. One had a low temperature of 37 degrees and a high of 53 degrees. The other design has a low of 29 degrees and a high of 44 degrees. The latter one was used only in the huge Impala/Caprice station wagons of the early to late 1970’s. Other part number differences are most likely to be related to mounting configuration or materials used in construction of the unit.

Link to comment
Share on other sites

Thanks again Joe, well I performed your test, and this switch worked perfectly 5 times in a row. I cleaned up the spade connectors and we'll see if I have an more issues????

 

On a side note, after shining a light into the opening for this switch, I could see a few leaves & debris stuck to the grillwork. With a modified 3/4" hose on the shop vac, I must have sucked out enough leaves & junk to fill a pint jar. How'd that stuff get there????

Link to comment
Share on other sites

Murphy,

There really isn't a filter in that system. Leaves and such that collect above in the space at the top of the cowl can, over time; get drawn in with the inlet air. A clean out is the only way to get it all out of there. You'd have to remove the right inner wheel well and all the associated brackets and equipment. Then remove the passenger half of the outer evaporator box/cover. This is no small project as it involves opening the A/C system to dismantle everything. Your method of using a shop vac and just working at it as best you can is the next best option you have. In doing this, take care not to damage the fins on the evaporator coils with the shop vac. It will reduce the amount of air that passes over and through them thus reducing your cool air inside.

 

If you have any other questions just ask. As I tell all my friends, "I can help you fix it or help you break it. We'll have to see which one it is". kicking

 

JC

Link to comment
Share on other sites

"Several sellers mention in their description "with auto-temperature control" What does that really mean?"

 

That is the set and forget system. Set your temp, turn on the system, and it automatically works to keep the interior at that temp.

 

http://automotivemileposts.com/autobrevity/atc.html

Link to comment
Share on other sites

Steve,

 

I saw that in some of the advertisements too and it made me wonder where they found that information.

While there are many parts listed specifically for the Auto Temperature Control feature such as; actuator, Amplifier Assembly, Aspirator assembly, bearing packing and many others, they do not list a difference in the ambient temperature switch.

I’d just like to know where those sellers found that information.

Link to comment
Share on other sites

"I’d just like to know where those sellers found that information."

 

I'm sure some sellers are basing their info on google searches and past ebay ads. Research, as Murphy is doing here, is a must before buying.

Link to comment
Share on other sites

The odd shaped rubber boot at the bottom of the evaporator box, I'm assuming, is to keep debris from plugging the drain. Mine is torn and barely hanging on, any one have one off a parts car they can part with?

In Arizona, the heat is murder on rubber, plastic, and wiring and finding one at a junkyard is futile.....

Link to comment
Share on other sites

Join the conversation

You can post now and register later. If you have an account, sign in now to post with your account.

Guest
Reply to this topic...

×   Pasted as rich text.   Paste as plain text instead

  Only 75 emoji are allowed.

×   Your link has been automatically embedded.   Display as a link instead

×   Your previous content has been restored.   Clear editor

×   You cannot paste images directly. Upload or insert images from URL.

×
×
  • Create New...