Heater issues

[brandoncpm]

Well, I got the heater blowing air, that's a step in the right direction. The only problem is it's cold air and not the AC kind. I am assuming the heater core is bad? I can't see any reason why the heater would be blowing air that is outside temperature (cold) when the hoses are all connected and the truck is warmed up to temperature. I drove the truck to work yesterday which is a 40 minute drive and nearly froze to death. The air temperature never changed after switching through all the settings on the controls. Oh yeah, when I tried to start the truck and drive home I had no power. Checked all connections, fuses, old crappy wiring, called the wife to come get me and just about that time I found a burned up wire that feeds the fuse box or panel. Chopped that out and fixed it and wouldn't you know it fired right up. Still no heat all the way home, long drive in February with no heater.

[VetteVet]

Originally Posted by brandoncpm

Well, I got the heater blowing air, that's a step in the right direction. The only problem is it's cold air and not the AC kind. I am assuming the heater core is bad? I can't see any reason why the heater would be blowing air that is outside temperature (cold) when the hoses are all connected and the truck is warmed up to temperature. I drove the truck to work yesterday which is a 40 minute drive and nearly froze to death. The air temperature never changed after switching through all the settings on the controls. Oh yeah, when I tried to start the truck and drive home I had no power. Checked all connections, fuses, old crappy wiring, called the wife to come get me and just about that time I found a burned up wire that feeds the fuse box or panel. Chopped that out and fixed it and wouldn't you know it fired right up. Still no heat all the way home, long drive in February with no heater.

I can certainly identify with you on the cold air thing.
The fact that it's blowing cold air indicates that the air doors are working.If you are getting defrost and heat flow but it's cold air then the obvious thing is no hot antifreeze to the heater core just like the guys above said.

You have a blockage in the core or the hoses. Take the hoses off at the water pump and the manifold and put one end in a bucket and if you have a way to pump water or air through the other end you can test the core for blockage. If you get nothing one way then reverse the flow through the other hose. If you still get nothing then the core is blocked will have to be replaced. You will have to make sure the hoses are clear and that the water shutoff valve in one of them is open and working, if there is one.
Be sure you do not apply much pressure to the hoses as you could blow the heater core. Is there a possibility that there could be ice in the core from lack of antifreeze.?

A pre- test would be to get the engine up to operating temperature and then place your bare hand on both hoses. They should be the same temperature and if one is cooler than the other one then you aren't getting water flow through the core.

[brandoncpm]

So I got the heater blowing on 2 speeds now. I took the "resistor" and cleaned the terminals, cleaned the mounting holes and screwed the piece back to bare metal making sure to ground the box as well as the wire for the ground. Now I have two speeds but not 3 like I should. Would like to just replace the resistor but cannot find one at any auto parts store in the area. NAPA and Shucks/O'Reilly didn't list anything in their catalog and said I was out of luck. Can this really be? Where might I find this elusive part? I also did not get any hot air blowing, just cold air. So long story short I have purchased a new heater core and blower motor. I don't believe I need the blower motor but while I am replacing the core I might as well do it since I have no idea how old the existing blower motor is. I did feel the hoses going to and from the heater core and both felt warm however I still didn't get any hot air blowing on any setting on a half hour drive so I believe the core must be the culprit? Sorry for the long winded post.

[brandoncpm]

So here are a couple of pictures of what I am talking about.

[brandoncpm]

Sorry, picture #2 is just my passenger side mirror, not sure why that got posted but I am looking for the matching driver side mirror if anybody has one in the southern oregon area they might want to get rid of. Thanks

[72 K20]

Don't the AC systems have a vacuum controlled water valve ? It could be the culprit. How hot is the truck running ? I have had a thermostat go bad and really cut down on the heat.
Make sure that there is a thermostat in it. A lot of people think that you can run without a stat but they will run hot in the summer and cold in the winter.

I usually run a 205 degree thermostat,, makes good heatin the winter and runs fine in the summer.

Tom

[THE BOSS]

Originally Posted by VetteVet

Attachment 1055749

the part in your pic is a relay, look for ^^^^^

also get a temperature gun, get your engine up to operating temperature. scan the engine where coolant is, scan the hoses and see what the temps are going in and out of the cab (heater core)

is the engine even getting up to temp? is the intake manifold around 180 degrees?

if the core is completely plugged up there will be no flow and no heat, hoses will be cool to cold. if you have a water valve, it may be closed
my 72 had a vacuum controlled water valve.

if you have say 180 degrees going in and 160-170-180 degrees going out, you have something in your cab shut off.

take your heater core hoses run some water through it with a garden hose to see if it is plugged up.

[brandoncpm]

Thanks for the info, will do both these things as soon as I get a chance.

[brandoncpm]

Well, I haven't solved the heat issue yet, I have two speeds of blower, not three, and all I get is cold air. I noticed a junction in the hose that comes from the block to the heater core that has a cylindrical plastic coupling with a small attachment on top that looks like it may go to a "Vacuum line"? If this is for a vacuum line that may open the valve to let hot water/antifreeze flow through? Could I take this out completely and just have the hose go from the block to the heater core without a splice in between? I will get a picture of it as soon as I can. Thanks

[brandoncpm]

SUCCESS!!! Well after finally getting a minute to work on my truck again I noticed something that had bothered me before but hadn't really clicked until today. The hose that goes from the intake to the heater core has a junction in the middle of it which looks like a homemade splice that kinda resembles an irrigation valve? It just seemed funny to me that the truck was getting up to temperature and the blower was working so why was there no heat? I was planning on replacing the heater core but this was my final step before doing that. I bought some rubber hose at NAPA today and chopped out the old spliced hose and put in a one piece section of hose from the intake to the heater core and YEAH BABY I finally have heat in my truck. Thanks for all the advice and suggestions from everyone along the way. I will be needing much more in the future as I am going to start a 6.2 diesel swap thread next week after I pick up my donor truck tomorrow morning. Will post pics and story in a new thread. Thanks guys.

[TonyJohnson]

Just know that without the valve, the heater core will get hot engine water all the time. It will make the cab hot in the summer...

[jaywashburn]

Brandon,
for some of those elusive parts for your truck I found a source that you might want for future needs. Rebuilt my entire heater system & they had everything for it (www.truckandcarshop.com). At some point you will want to replace the water bypass valve as mentioned earlier.
Good luck...

[brandoncpm]

Hey thanks for the info, just curious do all these era truck have this bypass valve? and if I want to keep it, how would I make it work as it was stuck closed? It looks like there is a spot on the valve for a vacuum hose but where would that hose go? The truck currently has NO vacuum connections anywhere as the whole heater system has been replaced with one from god knows what from the junkyard years ago. Also, will check out that site for sure to see if I can get the Fan speed resistor or rheostat or whatever it is actually called, no parts house in the area has one or can get one. Thanks.

[TonyJohnson]

http://www.lmctruck.com/icatalog/cb/full.aspx?Page=118
http://www.lmctruck.com/icatalog/cb/full.aspx?Page=153
http://www.lmctruck.com/icatalog/cb/full.aspx?Page=121

All the vendors here sell these parts. I included these pages because they show the parts and their relationships. Check out the vendor links here: http://67-72chevytrucks.com/vboard/f...play.php?f=195

[jaywashburn]

I believe all 67-72 trucks, suburbans, & blazers possess the water by pass valve. For $ 30.00 you can get a new one; I would just replace the old one.
The vacuum connection @ the valve travels through the firewall to the vacuum control switch (located behind the heater control panel). From that point you have vacuum hoses coming out to vacuum actuators that control the outside air door & recirculated air door (@ kick panel).
FYI: check out Ebay to pick up a used service manual for Chevy trucks (c10-c30) for that era. It will show all of the diagrams for wiring & vacuum hook up on the heater system.

[brandoncpm]

Will definitely check that out, need to figure out where all the vacuum hoses need to go, there are a lot of them dangling under the dash with no homes......