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.

[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.




.

[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.

[69sixpackbee]

Why in the world would you ditch the original POA and go with one of those P.O.S. POA eliminators??? You went through all of the trouble of taking off the other system and you will soon find out that the orig. A6 compressor won't live too long cycling on and off. Take my advice and put the POA back on and recalibrate it to run on 134A http://www.autoacforum.com/messagevi...&threadid=6974
You will be glad you did!

Bud

[FrankC]

Ok - received the Vacuum Reservoir Tank and it has a mounting bracket built in. So it has two screws on the evaporator core case - so I am good there.

Looking at the resevoir, there appears to be a 1/4 inch inlet and a smaller 3/16 inlet. Not sure it matters, but think the larger one connects to the manifold vacuum port and the other to the control head.

I really appreciate the responses - it helps piece things together greatly.

Frank

[FrankC]

Progress!

I was able to reconstruct the missing parts - heater control valve, Vacuum resevoir, lines, grommets, etc... . In addition, I took the time to clean the boxes up and will put in new seals and ducting.

Afterwards, I noticed the Control Head Vacuum Switch (two port) has a leak.

Is this part serviceable? Or can I simply purchase it new? Or do I need to find a donor part? Everything else about the unit is in really good shape - so buying a new unit would be overkill.

Anyone have a source??

[69sixpackbee]

Hey, Frank,
Take that vacuum control switch off of the control assy. and take it apart. It has just a circlip holding the two segments together. Lap the surfaces with some 600-1000 grit paper on a flat surface. I used a granite block here at work but you can use maybe a piece of glass or a mirror for a surface. Get those things good and flat but don't take too much off. Coat the surfaces with silicone based or lithium grease and put it all back together.
It will work fine once again.

Bud

[FrankC]

Hi Bud,

Thanks for the tip. I will give it a try. It appears to be riveted - but will pull it out for closer inspection.

Frank

[stsalvage]

Originally Posted by FrankC

Hi Bud,

Thanks for the tip. I will give it a try. It appears to be riveted - but will pull it out for closer inspection.

Frank

Just one question on your build have you gone to new ducting under the dash reason why i ask most of the time the flapper is damaged or cracking and you wont get a good enough shut off of heat and cold Air its best to buy it new Me i rather by the repop controller do to the wear and tear on the leavers.Its just a matter of time to brake one remember to change all your metal cables cus they get rusty you brake your leavers i'm working on mine remember to change the relay behind the glove box it's a pain to get to but its there. trust me you don't want to go in trying to replace it you have to remove the glove box and door and some hoses to get to it

[69sixpackbee]

Originally Posted by FrankC

Hi Bud,

Thanks for the tip. I will give it a try. It appears to be riveted - but will pull it out for closer inspection.

Frank

Your're right!
I forgot that mine was riveted and I made the pin with circlip groove and topped it with a Belville washer
Either way you can drill it out and replace it with like a #4 SHCS washers and nut too.
Good luck,
Bud

[69sixpackbee]

Originally Posted by stsalvage

Just one question on your build have you gone to new ducting under the dash reason why i ask most of the time the flapper is damaged or cracking and you wont get a good enough shut off of heat and cold Air its best to buy it new Me i rather by the repop controller do to the wear and tear on the leavers.Its just a matter of time to brake one remember to change all your metal cables cus they get rusty you brake your leavers i'm working on mine remember to change the relay behind the glove box it's a pain to get to but its there. trust me you don't want to go in trying to replace it you have to remove the glove box and door and some hoses to get to it

I separated my flapper box and repaired the unit. I made some gussets out of aluminum sheet and drilled through the shaft, riveted it and epoxied the gussets to the flap. They do sell repops at about $100.00 too if you want to go that route.

Bud

[FrankC]

Hey Bud,

I know what a Belville Washer is - but what is a #4 SHCS washers and nut?

Any pictures?

Thanks for your help.

Frank

[FrankC]

Whoops - Google is your best friend......

a #4 Socket Head bolt, washer and nut!

Thanks,

Frank

[FrankC]

I will need to purchase the 'S' duct, as it is cracked. My flapper looks weak, so I will try to repair as described.

On the control, I am using a #4 socket head screw a spring washer and nut. Still getting leaks with grease. Experimented with Loctite 501 I believe (non-hardening) TFE based sealer used in air cooled engines and that appears to work best. However - I am afraid it could plug the lines.

I may try to salvage the rivet I drilled out. I thought about re-using it - tapping for the #4 screw and use that and a spring washer to see if a mechanical+grease seal would do the trick.

Will let you know how it goes.

Frank

[FrankC]

Rebuilt the Vacuum Selector - better. It will hold vacuum, but when I swtich it, it will leak then hold vacuum again. So I can get heat out from the heater control valve. Posted in the classifieds - a WTB for a vacuum selector.

S plenum is cracked - so I ordered a new one.

Will try to strengthen the flapper on the diverter this week.

Harness is good enough for testing - but will probably end up replacing with a new one. Too many cuts and tape.

A/C High Speed Relay question: Ground wire from relay to firewall - where on firewall? I have the A/C harness grounded to the mounting screw of the relay on the core box (factory location) and built a ground wire from the relay to the firewall. Can't seem to find a hole on the firewall for the other end. Can anyone help.

A/C Compressor - diode at the harness - anyone have a value and rating?

Frank

[VA72C10]

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