71 Cheyenne Forensic Heat A/C Rebuild

[FrankC]

Getting around to tackling my issues with heat and air this weekend and discovered the PO had removed or bypassed several key parts of the heat and A/C systems. It is factory installed air.

I am missing the Vacuum Reservoir and A/C Heater Valve for starters.

I have the location for the A/C Heater Valve and purchased a new one today.

I will be ordering a Vacuum tank, but need a picture of where it mounts on the firewall (if that is indeed where it goes). The hoses from the control were of course rotted, but push through a firewall grommet. (I assume the two hoses come out there.) One should go to the vacuum tank, the other would go to the A/C Actuator under the hood and it has a 't' to the heater control valve.

My control head vacuum switch has only 2 ports, not three. Was there a change in 71?

The vacuum canister should have another line that attaches to a source. The PO put a Holley Dominator manifold, so I will need to find a port there or on the base of the carb.

In the interior, should the passenger kick panel actuator have only the diaphram without a manual override like the driver's side? In otherwords, do factory air trucks have only an actuator on that side?

Final question: Anyone using Silicon based vacuum lines? Does anyone have a good source?

Thanks and sorry for the long post.

Frank

[FrankC]

ttt - a picture would be great. Any 71 or 72 owners there have pics to share?

Obtained parts - except vacuum hose.

[Classic Heartbeat]

I will be ordering a Vacuum tank, but need a picture of where it mounts on the firewall

Mounts on the evaporator core housing.

Final question: Anyone using Silicon based vacuum lines? Does anyone have a good source?

I purchased mine from O'Reillys.

Now to the vacuum line routing....... Lets see if I can remember this off the top of my head...
The first line goes from manifold vacuum source to the vacuum reservoir mounted to the evaporator core housing.
From there you run a line into the cab to the input side of the heater & A/C control.
From there to above the heater core box, where you will place a "T".
Run a line from the "T" to the vent door vacuum actuator. Run another line from the other side of the "T" outside the firewall toward the firewall vent valve actuator. Just befor the firewall vent valve actuator you will place another "T in the line. Run a line from the "T" to the vent valve actuator and the other side goes to the hot water shut off valve.
This is not the way it was routed from the factory, but because you have only a 2 possition Heater/AC control this is the way it should be done. WES

[Andy4639]

Here is my factory looking system. It has been swapped out to run 134-A now though.

[FrankC]

Thanks to everyone who responded.

Is there a seperate bracket to mount the Vacuum Reservoir or is it molded to
the part itself?

What size vacuum line 3/16 or 1/4 inch OD?

[Andy4639]

Here is another schematic for you.



Mine are 1/4" if I'm not mistaken.
Oh the driver's side is manual the passenger side is auto but some leave the rod on it after they swap. I never hooked mine up at all to the vacuume lines.

[john]

Originally Posted by FrankC

Thanks to everyone who responded.

Is there a seperate bracket to mount the Vacuum Reservoir or is it molded to
the part itself?

What size vacuum line 3/16 or 1/4 inch OD?

I think that bracket is used only on 4X4's. classic heartbeat pic is for 2WD. Dont know line size offhand.

[BobbyK]

Here's a link to All the pic's I took when rebuilding my 71 Blazer's factory A/C system.

http://public.fotki.com/blazbk/blaze...d_of_ac_syste/

The pic's show the whole system dissembled,cleaned and either painted or powder coated, then reassembled.

This is the unit all "prettied up" before being re-installed.











.

[BobbyK]

Oh ya... I converted to R-134 during the rebuild.




.

[VA72C10]

Good info in this thread for me when I re-install my system