78 gmc heater temp control

[78gmc1ton]

My heater control valve is missing from my truck and in looking for a replacement I have found that there are 2 different ones, 1 rpo code c41 and the other rpo code c42 and seeing that I dont have the old one to compare with I am trying to figure out which one i need. Is there any way to tell which one I need? Thanks in advance for any help!

[grampadirt]

Is there a Pick-A-Part near you?If so go there and look around,you might get lucky and see an example of what you need.

[Duelin]

Can you find the RPO code label. In the newer vehicles it is in the glove compartment. See if you can fine it and check and see which option you have.

 

Example.

 

https://www.google.com/search?q=picture+of+RPO+code+label+on+a+gmc+sierra&biw=1126&bih=865&tbm=isch&imgil=Sr7uhBcAd8zF9M%253A%253BAfua7Wwga4idvM%253Bhttps%25253A%25252F%25252Fmarksautoparts.wordpress.com%25252F2013%25252F01%25252F21%25252Fgeneral-motors-service-parts-identification-label-explained%25252F&source=iu&pf=m&fir=Sr7uhBcAd8zF9M%253A%252CAfua7Wwga4idvM%252C_&usg=__P4xR2bbHaM-1IInqpaRdmh-MX70%3D&ved=0CDEQyjdqFQoTCO7Ew8rG7MYCFQHugAodtkMGIw&ei=4WauVa7QCIHcgwS2h5mYAg#imgdii=Sr7uhBcAd8zF9M%3A%3BSr7uhBcAd8zF9M%3A%3BKb1qWoppyjACvM%3A&imgrc=Sr7uhBcAd8zF9M%3A&usg=__P4xR2bbHaM-1IInqpaRdmh-MX70%3D

[78gmc1ton]

I think I am going to check the local pull a part, they have several 73-87 chevy and gmc trucks and given the low cost I will grab a couple different ones and try them. My RPO code sheet is missing so I dont have that to work off of, I dont suppose I can use the vin to make another sheet? Thanks