Heater, Hoses, and Vacuum testing

[mpierce9]

Hello, I have a 1975 K5 Blazer with Air Conditioning.

I would like to test my vacuum lines in my heater setup.


I get zero heat from my heater after driving my car 30+ miles. This is the position I set my heater controls while I'm getting cold air through my vents.



Here's a recap of what has been done:

1. Water pump replaced
2. Heater core flushed including inbound and outbound heater core hoses
3. Entire cooling system flush (after heater core flush)
4. Cooling System "Burped"

As I move through the different sections here, Off, Vent, Heater and Defrost, air comes through the different areas of the duct system or turns off completely when in the Off position. There is no change with the other positions (A/C or BI-Level)


Here is a current state of the hoses after the car is "warm". Notes are in the image, but just in case. The upper hose is 3/4" and delivering from the water pump to the heater core. The lower hose is 5/8" and delivering from the heater core to the radiator. I have an additional note in the image about a black piece of equipment, if you happen to know what that is.



Inside the cab, both above the transmission hump and behind the glove box are small pancake vacuum actuators. I would like to test these. See image below. I also understand there is another one nested deep in the bowels near the heater core.

A secondary note about the image below. The pancake on the right side of the image opens a port to the exterior of the truck. I can push it open with my hand. I have never seen this actually do anything when changing the different positions of the control panel. I'm not sure if i should be able to witness this change when I adjust the control panel positions or not, but I feel like I should. This is the cornerstone of why i want to test this vacuum system.


After flushing the heater core with no issues and running the system with no leaks I feel good about the state of the heater core.

Everything I've read mentions that taking the heater core section apart is a bear of a job. If I need parts that i have to order online i'd like to go ahead and order them all and be done with it.

If you have any other insight on parts that would be good to order, how to pre-test to see what's working or other general advise I would be very thankful for it.

I've read up on these links



http://67-72chevytrucks.com/vboard/s...d.php?t=463885
http://67-72chevytrucks.com/vboard/s...=397868&page=4
http://forum.73-87chevytrucks.com/sm...p?topic=1949.0
http://coloradok5.com/heatercore.shtml

[BMERDOC]

Have you bought a vacuum pump to test the lines and diaphragms? What condition are the lines in? I suspect you have already chased each line to check for leaks. Correct?

[mpierce9]

I have not purchased a vacuum pump. I was not aware of how (or what) to test these lines with. The lines visually appear in reasonable condition from what i can see without removing panels or digging deep into the system. The tips are hard but overall there do not appear to be any easily noticeable cracks or splits. I have not inspected them with a lot of diligence. When you refer to a leak in the line, how are you aware of it? Does the line whistle, or provide any other sign of leaking?

[BMERDOC]

I'm not an expert in these systems but I would suspect that the system has a main vacuum supply, some sort of manifold, switches and the shown diaphragms. A line could possibly whistle or make a sucking sound but I wouldn't count on that. I would get a pump and check the diaphragm and vac line at the diaphragm. Pull vacuum and see if you can maintain it. I'm not sure if there is a check valve in the system. Can you chase down a diagram for us to look over? Here is a Mity-Vac pump at HF. There are cheaper ones but I recommend this one.

http://www.harborfreight.com/mityvac...ump-39522.html

[BMERDOC]

Found a thread that may help you.

http://67-72chevytrucks.com/vboard/s...d.php?t=549887

[mpierce9]

excellent link, thank you.

[BMERDOC]

You're welcome! Look over it and see if you can find an answer. If not, you know what to do.

[Dead Parrot]

The hot/cold slider is a cable connect to a flapper behind the glove box. That cable connects to the flapper via a plastic piece. If the plastic is broken, no hot/cold adjustment. Pulling the glove box lets you check that easily.

[mpierce9]

Thanks for responding. When i adjust the lower slider (Cold - Hot) I get these two images.

With the lower slider set on Cold this is the position.



With the lower slider set on Hot this is the position.


As you can see the arm is moving as i make adjustments on the control panel.

Another question resulting from this research. Please see the image attached.

[cadillac_al]

I would have bet money on a cable problem, but it seems to be working. The vacuum sounds like it is working because it redirects the air correctly. The heater hoses are getting hot. I would double check on the flow of the heater core by watching it dump into the radiator. Just take the radiator cap off while cold, start truck and watch the water dump in. If it flows good then...............you are screwed because everything is working.

I don't really know what that blend door looks like but maybe it is stuck shut and the lever still moves somehow???? It's a stumper.

[mpierce9]

ok, it is Christmas day currently, but tomorrow morning i'm going to open that rad cap, park it high on a step hill and burp it as much as possible. once I get as much fluid as I can in the system I'll obverse the return dump back from the heater core. I will report back once I haver completed this exercise.

Thank you again for the assistance.

[augwld]

The top heater core hose should be going to the intake manifold and the lower one either to the radiator, or water pump. It sounds like you have both hoses hooked up to return and no feeder.

[wilkin250r]

I wish I had jumped in this thread sooner, but augwld is right.

You have both hoses hooked to the low-pressure side of the water pump. Basically, you have both hoses hooked to "return", there is no pressure difference to push fluid through. You've got very little flow. One of those hoses should hook to the intake manifold, that is your "feeder".

If my memory is correct, I believe the 5/8 hose should be your feeder, (from intake manifold to heater core) and the 3/4 is the return (from heater core to radiator).

[mpierce9]

We found a resolution in this thread which is exactly what you guys said above. I certainly appreciate the insight from everyone. I now have heat and was thanks to each of you.

Other thread that ended up being a related topic

Why did people route their heater hoses to two returns? Is there a logical reason for this?

[BMERDOC]

Glad to see you got it working!

[wilkin250r]

Most people don't understand that, as a general rule, every single hose fitting on a waterpump is an INLET. It's on the low-pressure side of the pump. The only output a water pump has is to the engine block.

All heater hoses I've seen feed from the intake manifold. I believe on manual transmissions, the return comes back to the waterpump, on automatic transmissions the return comes back to the radiator. I imagine this is to give a little bit of early heat to the radiator and the transmission cooler inside to help warm up the transmission fluid.