72 MC 350 A/T - Blower A/C Heat

[B-Man]

Ok guys and gals. There are a lot of REALLY good posts on the topic. And I've learned a lot by reading through them. But can anyone point me to specific links / vendors for replacement parts for my 72?

- Blower Switch (in dash)

- Blower Ambient Switch (mounted in plenum)

- Blower Resistor (mounted in plenum)

- Blower Relay (mounted on top of plenum)

 

The forensics:

- All of my fuses are good, proven with a test light on both sides of the fuse.

- Running a ground wire directly from the battery to the black wire plug from the relay, and a power wire directly from the battery to the purple wire spade in the relay plug results in the blower motor properly running (though seems soft).

- Turning the key on and running the blower switch up and down yields no blowing / flow ... nothing at all.

At this point I have access to everything and might as well open up the parts cannon. So where do I get good replacement parts?

[B-Man]

Ok, maybe I'm answering my own question a bit, but still looking for confirmation from the forum team here.

SWITCH

https://www.thepartsplaceinc.com/product/1972/1972-chevrolet-monte-carlo-blower-motor-switch-with-a-c-gm-6273383/93074

 

AMBIENT SWITCH

(?)

 

RESISTOR

https://www.thepartsplaceinc.com/product/1972/1972-chevrolet-monte-carlo-blower-motor-resistor-with-a-c-4-prong-gm-3949879-6262651/93621

 

RELAY

https://www.thepartsplaceinc.com/product/1972/1972-chevrolet-monte-carlo-blower-motor-relay-with-ac/44931

 

[cbolt]

The resistor itself rarely goes bad. The relay (which happens to be both links you posted) is the most likely suspect, however if you are ordering parts I would order both. 

You can check the switch continuity with a ohmmeter if you want first, or clean the switch with some of that spray electronic cleaner or denatured alcohol. If the switch contacts are corroded that will only be a temp fix tho. 

[B-Man]

@cbolt, thanks for the input 

I corrected the Switch link. Thanks for that 

So the relay is the most likely suspect, agreed. Seems like the resistor is easy enough to buy and replace, so might as well.

The switch seems like a pain in the butt to replace. But the dash pad is already off. So maybe it's not that bad. A lot of obvious rust / corrosion on the switch so seems like another no brainer.

But what's the deal with the 'ambient switch'? Any idea of that fails? And where to get one, while I'm at it?

[B-Man]

It was the relay. I popped the new one in and the HVAC panel came alive!

I went ahead and replaced the resistor since it was easy to do.

I haven't swapped out the switch in the HVAC panel yet. Will do that tomorrow if it's easy enough. Else, the new switch pill go in the miscellaneous parts bin.

As others have stated, that blower is WEAK! I will definitely have to figure out a way to address that. 

[cbolt]

I'm just going to piggyback on this thread and ask about the fusible link and fuse for the high speed blower circuit on a '72. Mine was completely melted making the fuse holder no longer serviceable so I need a new fuse holder and fusible link wire. Anyway, I found just the female fuse holder end, and it looks like the other end, male end of the fuse holder, is only available if you purchase the entire A/C harness unless I am missing something. Do I need to add fusible link wire to this frankenstein style setup as well? 

[B-Man]

@cbolt, you can see in my photo that a 30 amp 'blade fuse' is installed in my 72.  I would imagine that the OEM was an inline AG fuse.  I recall cleaning up the installation of the 30 amp blade fuse when I first bought the car and found all sorts of poor wiring connections.  But I dont recall me being the one who cut out the AG fuse and installed the blade.  Regardless, that's all you need to do to make it functional.  You can get a blade fuse holder, with fuse, at your local auto parts store, Walmart, Amazon, etc.  If you're trying to maintain an OEM look, then that's a different story.  I cant imagine you would replace an entire harness to satisfy the need for a fuse, but maybe that's what youre in to

[cbolt]

1 hour ago, B-Man said:

@cbolt, you can see in my photo that a 30 amp 'blade fuse' is installed in my 72.  I would imagine that the OEM was an inline AG fuse.  I recall cleaning up the installation of the 30 amp blade fuse when I first bought the car and found all sorts of poor wiring connections.  But I dont recall me being the one who cut out the AG fuse and installed the blade.  Regardless, that's all you need to do to make it functional.  You can get a blade fuse holder, with fuse, at your local auto parts store, Walmart, Amazon, etc.  If you're trying to maintain an OEM look, then that's a different story.  I cant imagine you would replace an entire harness to satisfy the need for a fuse, but maybe that's what youre in to

I saw what you had done, and considered it however I found the fuse holder at the local place and was just wondering if the other end, the male end, was available and whether or not I needed to add a fusible link to the whole sha-bang

[jft69z]

54 minutes ago, cbolt said:

... and was just wondering if the other end, the male end, was available and whether or not I needed to add a fusible link to the whole sha-bang

No fusible link needed, the fuse will be protecting the circuit. Make sure the parts you're buying have the capacity to handle the current of the load (30 amps in this case). 

[cbolt]

54 minutes ago, jft69z said:

No fusible link needed, the fuse will be protecting the circuit. Make sure the parts you're buying have the capacity to handle the current of the load (30 amps in this case). 

Thats all I needed to know. Thanks