hvac is gonna be the death of me

[novassracer12]

hey everyone! im new to the site. I have a 73 c10 Cheyenne with a 350 th400. I have an issue with the hvac. I have searched for days (literally days for something even close to my problem. the fan is not spinning as fast as it should. I have already replaced the fan with a new one from a 94 Silverado, replaced the fan relay 4 times and finally yesterday I was at pick n pull and grabbed another one in hopes maybe it had something to do with new cheap china ones, replaced the fan resistor. It does work on low. when I remove the orange wire from the plug at the relay and jump it to the motor it spins a lot faster. my duct work is all solid, tight and sealed, vacuum line from manifold to vac reservoir is connected. im at a loss with this. thanks!

 

[350runner]

Welcome from Texas. Fan switch maybe?

Sent from the dust in front of you!

 

[novassracer12]

how interchangeable are the dash switches. when I was at the wrecking yard yesterday I seen a few from lat 70and newer but nothing from a 73. they have different settings then what I have

 

[89Suburban]

Just find a cheap new switch on line. I think I paid less than 10 bucks for mine.


Sent from the *******

 

[highdesertrange]

here we go again replacing parts that are not bad. find the shop manual for your truck(available on this site for free). find the trouble shooting section for your problem. find your problem and fix it. lots cheaper than throwing money and parts at it. highdesertranger

 

[350runner]

here we go again replacing parts that are not bad. find the shop manual for your truck(available on this site for free). find the trouble shooting section for your problem. find your problem and fix it. lots cheaper than throwing money and parts at it. highdesertranger

If the op has already replaced all the other system components what else is their left?

Sent from the dust in front of you!

 

[novassracer12]

highdesertrange im no newbie to wrenching. 20 years and counting plus own a successful shop. the parts needed to be changed. I wanted the fan update because everyone says it moves more air. the original relay had separated between the case and plastic, the resistor was aged pretty bad from the many years of use. so as stated from my first post Im new to the site. in fact im not the best at this computer stuff so I didn't know where to get the manual on here so if you could please explain where I go to get it. thanks

 

[chengny]

Make sure the power and ground for the control side of the relay are good. There should be an in-line fuse in the orange lead that ties into the firewall junction block and runs to the relay (different than the orange lead from the dash switch). Check that fuse - and also make sure there is continuity to ground from the negative side of the coil (a black lead from the relay):

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[novassracer12]

thanks chengny, I will be checking that out today and get back.

 

[novassracer12]

chengny, I do not have power at the smaller orange wire on the relay or ground. the blue wire has 3.88 volts, the larger orange wire has 12.68 volts and the purple wire has 3.88 I tested it with engine off key on fan speed high and heater & ac. I will run a ground jumper to it and apply power with a power probe. hard to see in the picture you posted but does the wire #52 go to the dash selector switch?

 

[novassracer12]

ok so the black wire-ground off the relay coil is infact grounded properly. hopefull its just something unplugged at the dash control. going out now to go find out.

 

[novassracer12]

chengny thank you for the diagram. helped out big time. the problem was the fan speed switch. the years got the best of it. I applied power at the orange wire on the back of the switch and fan speed went up. after messing around with the switch and putting it between high and next speed down I would get full fan speed. just pulled one from another truck I have here in the yard but does anyone know if this switch can be found new?

 

[chengny]

NOS - $28 at Classic Industries:

G2900 - 1973-82 HEATER AND AC BLOWER SWITCH
Original GM blower motor switch for 1973-82 pickups with air conditioning and 1973-82 Blazer and Jimmy models with air conditioning.

You must be registered for see images attach

http://www.classicindustries.com/product/1973/truck/parts/g2900.html

 

[novassracer12]

going to order a new switch. started pulling duct work out to clean and found a can of worms. so now its all coming out to scrub the duct work and fix a few broken things. I remember seeing some plastic tabs in another post. I got some foam tape for the box doors and to seal around the seams. I also picked up some foil tape. tomorrow I will order a new evaporater. is there anything else I can do with the stock setup to improve its efficiency. I tried posting a few pictures but cant figure out how to make the pictures small enough to upload

 

[chengny]

I tried posting a few pictures but cant figure out how to make the pictures small enough to upload

Use an outside image host. They accept huge images. Then just copy the URL link and post a thumbnail here. The viewer can then click to enlarge the image.

This one is safe and free - you just have to register

http://www.turboimagehost.com/