Replacing AC compressor and fan relay

billpatterson

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Hi there,

Below are Notes I took that describe what I have done regarding, 1. tracing wires and removing the black module/box, 2. testing relays, 3. proper connections, 4. AC fan and temp switches

I think the wiring upfront is OK. I am suspecting the problem is the AC temp switch as its the only aspect I have not tested. Going to look into how to test it unless someone here has a testing procedure?

Thank you again!

Accessory black box for aux fan
-gr=green, wt=white, br=brown, bk=black
-gr/wt and br/wt from black module box/relay went across front off car alongside the 12v red lead for aux fan
-br/wt patched into br/wt lead going to temp sensor on coolant divider
-gr/wt plugged into transparent connector block behind the brake booster. This connecting block was associated with zenith carb circuit

-bk/wt went to relay 86c on AC relay
-br which was ground
-gr/wt described above
-br/wt described above
*black box and wiring removed

Testing relays
-12v lead across front of car is good ~12.4v and has continuity when both ends disconnected
-tested function of my original relay and 2 aftermarket relays,
-my original relay does not have resistance between 85 and 86 = does not pass test
-aftermarket relays do have resistance between 85 and 86 and passes following relay test video
-tested relays following this video

Connections
-check for proper connections,
-properly connected to relay following diagrams and Chris’s message
-12 v is 30, aux fan is 87, 85 ground, 86 temp switch
-swapped 85 and 86; no change
-current connections at relay do not contain the 86c connection (on the original relay) back to the black module. It was installed at the dealer to turn on the aux fan when the engine got to a certain temp. If I was to add a circuit to run the aux fan to help the engines fan, I would use the (adjustable) Painless aux fan wiring kit.

AC switches
-AC fan switch circuit is working; AC switch turns off heater fan and can hear its relay click when switch on
-AC temp switch? Maybe temp switch is bad as it excites relay therefore ac pump and aux fan

Regards,
Bill

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billpatterson

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The box is still available in Germany

Hi Don
Good to know!
I removed the black box as part of understanding and addressing the AC not working issue I have. Its wiring was not the issue. BTW really like the Painless wiring kit for the aux fan. The car though runs below the 1st mark on the temp gauge :)

Bill
 
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billpatterson

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Hi
I have done a few more test suggested by HBChris (THX!). With good news at the end! These tests test the wiring and AC temp switch upstream of the relay, aux fan and AC compressor.

1. Directly power the relay from battery to 86 terminal. Result - powered aux fan and engaged the AC compressors coil; we know the relay and related wiring is OK

2. Test for 12v from AC Temp switch to 86 terminal. Result- no 12 v; circuit meter bounced between 0.5v and 0 ohms; we know its upstream of the wire connection on the AC temp switch.

3. Jump/bypass the AC temp switch. Result- Aux fan and AC coil engages; AC system blows cold; We know its the AC temp switch. Half ass Installed new AC temp switch and AC system reacts to different temp settings

However, the new temp switch is wrong configuration to mount on AC dash of my '73 E3; its base is too large (see post 21) compared to the original AC temp switch (see pics below). Watch out; same part number though!!

So...looking for a used AC temp switch. Anyone!!??

Kindest regards!

I hope this post helps others with their AC system woes.

-Bill

Bright test lamp; 12v going to AC temp switch
IMG_3157.JPG

Very dim test lamp; poor voltage out of AC temp switch; not enough to excite the relay
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Jumped AC temp switch; the AC system works again
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Original AC temp switch; anyone have a good used one for sale!!??

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HB Chris

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Congrats! The original threads are extra fine metric, the replacements are SAE and the post is larger. You can enlarge the hole as long as you have the thin nut to hold the new switch.
 

billpatterson

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Hi
I have done a few more test suggested by HBChris (THX!). With good news at the end! These tests test the wiring and AC temp switch upstream of the relay, aux fan and AC compressor.

1. Directly power the relay from battery to 86 terminal. Result - powered aux fan and engaged the AC compressors coil; we know the relay and related wiring is OK

2. Test for 12v from AC Temp switch to 86 terminal. Result- no 12 v; circuit meter bounced between 0.5v and 0 ohms; we know its upstream of the wire connection on the AC temp switch.

3. Jump/bypass the AC temp switch. Result- Aux fan and AC coil engages; AC system blows cold; We know its the AC temp switch. Half ass Installed new AC temp switch and AC system reacts to different temp settings

However, the new temp switch is wrong configuration to mount on AC dash of my '73 E3; its base is too large (see post 21) compared to the original AC temp switch (see pics below). Watch out; same part number though!!

So...looking for a used AC temp switch. Anyone!!??

Kindest regards!

I hope this post helps others with their AC system woes.

-Bill

Bright test lamp; 12v going to AC temp switch
View attachment 122234

Very dim test lamp; poor voltage out of AC temp switch; not enough to excite the relay
View attachment 122235

Jumped AC temp switch; the AC system works again
View attachment 122236

Original AC temp switch; anyone have a good used one for sale!!??

View attachment 122237

View attachment 122238

Hi
I found the AC temp switch I purchased using the OE part number is too long for the space for the original switch. But I found a aftermarket switch from Rock Auto and it fits and works. It does use a brass nut vs the original circle 'nut' but it works! I included pictures below. I have another on order from Amazon.ca which is actually made by the same company as the switch I removed (by Ranco/Made in Mexico); It'll be a back up. The Rock Auto feels a lil wimpy but...it works.

Regards
Bill


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72CS

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Hello Bill, Can you pass along the links to the Rock Auto and Amazon switches you mentioned? I tried using the PN from the pic but no luck. I have an intermittent problem with my A/C. I haven't finished checking things out but I seem to be only getting between 7 and 8 volts out of the temp switch (maybe this is normal?) and the fan relay might be wonky. Anyways I figured having the temp switch on hand would be a good idea... Thanks
 

billpatterson

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Hello Bill, Can you pass along the links to the Rock Auto and Amazon switches you mentioned? I tried using the PN from the pic but no luck. I have an intermittent problem with my A/C. I haven't finished checking things out but I seem to be only getting between 7 and 8 volts out of the temp switch (maybe this is normal?) and the fan relay might be wonky. Anyways I figured having the temp switch on hand would be a good idea... Thanks

For sure,

Rock Auto - https://www.rockauto.com/en/parts/gpd,1711239,a/c+thermo+switch,11284

Amazon.ca - https://www.amazon.ca/UAC-SW-6490C-C-Thermostat/dp/B003R43E0O

The Amzon.ca switch feels a lil better quality. Both are made oversees by the same company.


I had the same issue; lower voltage coming out of the temp switch,

Bright test lamp; 12v going to AC temp switch
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Very dim test lamp; poor voltage out of AC temp switch; not enough to excite the relay
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All the best,
Bill
 

sfdon

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Given up on sourcing the ceramic stock AC blower fan switch.

We use the Indak now.


Knowing that the original item (both versions) are NLA and old ones are often junk we decided to come up with an inexpensive basic unit for the cars in the shop getting AC work done.



This is a 2 stage AC blower fan switch from USA (Indak) that replaces the factory switch that has not been produced since 1992 and has since likely cracked from heat and turned green from corrosion.


It is not a potentiometer type like the original that gets so hot and cracks- there is no resister in the switch so it does not get hot.

When installed you have 2 speeds -off of course plus (low and high)

it’s plug and play- disconnect your current switch - plug in the 4 new connectors into the existing wiring and you are done.


Sorry- NOT FOR 1974 MODEL YEAR OR LATER CARS!
 

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72CS

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Thanks Bill! Already placed my order. My temp switch seemed to be acting like a random number generator, it would give a voltage anywhere from 1 to 10... I will probably try and clean the original unit, or just replace it.

BTW the Indak 2 speed switch seems to no longer be available.

Cheers
 

sfdon

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Thanks Bill! Already placed my order. My temp switch seemed to be acting like a random number generator, it would give a voltage anywhere from 1 to 10... I will probably try and clean the original unit, or just replace it.

BTW the Indak 2 speed switch seems to no longer be available.

Cheers
I ordered 10 today.
 

sfdon

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That’s a 3 speed fan switch. L M H

with only one resister in the box you need a 2 speed switch. L H


supply houses carry them.
 

Sean Haas

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I was trying to install sfdon's Indak solution, found the resistor in the evap box doesn't work. So if I want multiple speeds seems like:
-I have to replace this resistor, I know the originals are NLA and I thought I recall from somewhere that you can use one from an E12 or E21 but I don't see those either is there a way to replace?
-Use one of the freaky Indak switches with the resistor coils on the switch - but I didn't see any with 4 terminals, just B/L/H to run a fan but no C "common" terminal to power the compressor
-Live with my full-on only fan and be glad I even have air. Which is fine but it would be nice to tone it down a bit.
Suggestions welcome if anyone has tackled this.
 

billpatterson

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Hi Sean
It looks like other AC resistors may work; certainly worthy of further investigation.



Regards
Bill
 

Sean Haas

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thanks bill, was looking but didn't spot those - I did manage to find an Indak switch with the resistor at Napa for $20 and they had a good pic of the back - for the record the terminals are B,M and C- I'm going to see how that works since I've got the other switch wired in and if it doesn't I'll see about replacing the resistor, that first one you listed is probably pretty much the same as what is in there I'm guessing.

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sfdon

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Be careful- on a tired fan that coil will be glowing bright Orange.
at night it’s a sight to see.
 

Sean Haas

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Yeah, it concerns me a bit, since it was relatively cheap and since I know this kind of switch was used in a lot of applications I figured I'd see how went or if it would freak me out too much - my other thought being I have a hot coil either way, it's just that I can see this one whereas the other one is hidden in the evap box - I think from some old threads I came across if I'm correct you tried these for a bit before changing to the two-speed switch - would you just not do it? I can try to track down the resistor for the evap box and go that route instead.
 

HB Chris

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Where is this resistor? When I had my evap box apart I don’t remember this but it might just be old age. I do remember these in the 2002 heater box.
 
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