still no heat

[bludmon]

Hi everyone I just changed the thermostat in my 1994 Mazda Navajo. I know I did everything right because I started the truck up with the radiater cap off and the heat on with the fan on 2. When I did that I was getting good heat. Now a day later with the radiater cap back on and the heat on I'm getting no heat at all. My first guess would be the radiater cap but there is pressure in the radiater when I try to loosen it a little after I have it running. What baffles me is that I was getting pretty good heat the night before. Any ideas?

 

[StryctNy9e]

I think there is a couple of vacume lines that attach to a acctuator that is on the air intake that comes off the exhaust manifold. Make sure they are connected. It dosent sound like this is the problem because the heat was working a couple bays ago, but just a thought and somthing to start with or check. There was a thread on this site somewhere that showed me the diagram. Do a search and im sorry if I didnt offer much help. Good Luck.

 

[Roadrunner777]

Towards the back passenger side of the engine bay, there are the heater hoses... pretty obviously right over the top of the blower motor. There is, as Mr. S refers, a vacuum driven manifold there that controls passage of coolant to the core. You might check the temperature of those hoses, just to see if you have coolant getting there or not.

I'm thinking you have some burping to get done... there are some interesting methods (jack one side up) and some I don't understand (a funnel method?), I just keep checking and topping of the coolant reservoir until it stops needing it.

 

[bludmon]

I went out and checked what you guys said and the vacuum line is on the acutator. When I take the vacuum off,the acutator (I'm assuming)closes and when the vacuum is put back on(this is of course with the engine running and the heat on)it opens. I'm getting what is less than luke warm air. Should I assume that a heater core is in my future? Are they hard to put in? Thanks for the input guys. By the way I did try to "burp" it some more and I did get some more air out but I don't think there is any more.

 

[StryctNy9e]

There is a duct that attaches to the passenger exhaust manifold and lets heat inside the cab, maybe this is undone. Might be a little messy but pop off the heater hoses above blower motor and make sure they are getting anti freeze. On just feel them and make sure they are supplying warm fluid to core. It is possible the core is clogged but they typically start leaking when they fail, at least in my experience. I have only replaced a heater core in my chevy Nova, never in my EX.

 

[Roadrunner777]

I'm looking at this like... it started when he changed the thermostat. So, first, is the engine getting as hot as it did before? Are the hoses going to the core (at that manifold) too hot to touch? Change thermostat leads to severely clogged heater core just doesn't make sense to me.

 

[StryctNy9e]

yea I get what your sayin roadrunner777. Worst comes to worst he needs to drain the coolant, unhook the heater hoses and put his hose on one of them and make sure the flow is good through the heater core. Also did you put the air breather on the thermostat back at the top? dont know if this would do that but maybe you think you got the air out but if the breather is not at the top it may still have air in the hearet core.

 

[bludmon]

Thanxs for the response guys. Actually the reason I changed the thermostat is because I wasn't getting any heat. When I changed the thermostat and purged the system I actually got really good heat but since then no heat. The heater hoses do get warm to the touch but not real hot. When I squeeze the heater hoses you can see some of the antifreeze come up in the radiater with the cap off. This may sound like a stupid question but could the cap have anything to do with not getting heat? I know it holds presssure when I have it on but maybe not enough? I could just take the cover off for the heater core to see if its leaking but is it as easy to do as the Explorers are?

 

[StryctNy9e]

If the heater core was leaking you would smell the anti freeze in the car and on your carpets. Your problem has me kinda stumped and I will keep my mind open and if I think of anything I will let you know.

 

[Roadrunner777]

I don't think it's leaking, you would smell it, as Mr. S says. I read your original post early this morning and I used my last 5 minutes before work to look up heater core access in the factory books. It didn't say much! You go under the dash on the passenger side, and there are apparently 5 screws, and there it is. The book refers to a special tool to disconnect the core lines. I hate it when they say that.

If I wanted to prove this issue out, what i would do is get a loop of heater hose and hook it up at the vacuum diverter valve instead of the heater core and see if it gets hot. If not, forget about the core, it's on the engine side.

 

[StryctNy9e]

I think the tool is a fuel line dissconnect tool I forget the name, but I am pretty sure it is the same thing. Also use this tool on A/C lines, fuel lines, and fuel filter installation/removal.

 

[bludmon]

I just went outside and took the vacuum line off the acutator and now I have heat. If I put it back on I dont get heat. When I put the vacuum on you can feel something move. could that be the problem? Do I just leave the vacuum line off? When I take it off and I put my finger over it I dont feel any vacuum coming out of the hose. Thanks again guys for all your help so far.

 

[StryctNy9e]

Trace that vacume line and see if it plugged in at the other end, sounds like somthing is reversed or that your accuator is not working in line with your heating switches. I think that vacume line operates the acctuator for the heater/fresh air blend door.

 

[Roadrunner777]

Vacuum is on that line when the controls are set to OFF or MAX AC. The part you are working on uses the vacuum to close a valve which stops the flow of coolant to the heater core. This apparently is in response to an issue in the design where the heater core is not very well isolated from the A/C and people were complaining about weak AC. This same line also operates a door that causes air to recirculate unless it is on OFF or MAX AC, in which case the system draws outside air.

Anyway, you probably have if figured out from here. good luck!

 

[bludmon]

Ok i went out and checked were that vacuum line goes to and it goes to a cylinder behind the glove box which I assume is the door you guys are talking about. When I shut the heat off that cylinder sucks the door closed but when I turn the heat on that cylinder should open the door but it doesn't. That door does not open unless I take that vacuum line off. Then I have very good heat and the cylinder opens up. As soon as I put the vacuum line back on the cylinder it sucks the door closed and the heat starts to disappear. So do I replace that cylinder or is there something else I'm missing?

 

[Roadrunner777]

check for vacuum on the line at the various settings, OFF, MAX AC, PANEL, FLOOR (I forget them all and the order, but make a note. FYI, the COOL/HEAT control (the bottom slider) has nothing to do with any of this. The vacuum should be there if the setting is OFF or MAX AC, otherwise there should be no vacuum.

Anyway, If you can check vacuum at those settings, and post back. I'm done here for the night. I'll take a look tomorrow.

~Phil

 

[bludmon]

I went ahead and did that check like you said and the vacuum is there on every setting across the panel. The only way the vacuum isn't there is if I unplug the vacuum to that cylinder behind the glove box. If I put the selecter on panel/floor and unplug the vacuum,heat comes out real good. But if I plug in the vacuum on that setting the heat goes away and the cylinder closes that door. Thanks alot Phil I appreciate the help. If it wasn't for you and everyone else I would of went out and bought a heater core and found out I didn't need it. It's bad enough that I changed the thermostat when I probably didn't need to. But now I know that I have a new one in there so I don't have to worry about that any way.

 

[StryctNy9e]

sounds like roadrunner777 has got your back. I have never pulled my controls apart or dealt with the problem personally just read things about it. I will let him help you solve the problem so I dont start confusing you. It sounds like you are almost there.Good luck.

 

[Roadrunner777]

You got 2 choices now:

1 - The easy way - Disable the vacuum. The only real purpose of the vacuum line is to make the A/C work a little better, and that's only in MAX AC setting. This is really easy to do, just go to the vacuum tree on the manifold and find which one goes into the dashboard. Remove and plug the vacuum port.

2. - The hard way - The vacuum is controlled by the heater control panel. I would guess there is a displaced seal or it's just plain broken. Check it out, fix or replace. Junkyard part or you can get it new from LMC truck for $130.

I want to clarify something for a future reader:

The door that bludmon is talking about controls whether air is recirculated through the cabin or fresh air is used from outside. The main reason for this goes back to the idea of MAX AC. If you can imagine a car parked in the summer sun all day, it gets really hot inside, maybe 110 degrees. Now, you could try to cool that air by recirculating it through the AC, but it is more effective to use outside air, which is cooler than 110 degrees to start with.

The same vacuum line goes to a manifold valve on the heater hoses. This is only on 93-94, by the way. The idea is on MAX AC or OFF, the system shuts off flow of coolant to the heater core. There is apparently a shortcoming in the design, and heat from the heater core reduces the effectiveness of the AC. So, for MAX AC, they added this gizmo to shut off the flow of coolant.

This may be an un-needed complexity for some. I'm in cold climate, so I never use MAX AC, but I want to maximize my heat. So, now that I understand how this thing works, I'm taking it out and just run straight heater hose from the engine to the core. Probably need new hoses anyway.

 

[bludmon]

Well again thank you for your help. I think I will do option 1 because I have over 227,000 miles on it and my a/c doesn't even work anyway. If I wouldn't have so many miles on it I would probably fix it. Besides like you said Roadrunner I'm from a cold climate too in fact we had a freeze warning early this morning(May 16) and I would just rather have heat. If it's hot I will just roll down the window. Thanks alot for your help everyone. Now I can start working on rebuilding my 4x4 motor. I know this is off subject but can I take the motor and all the weights off and still drive the truck while I'm rebuilding the motor?