HELP! Struggling to get heat and its winter in ohio

[paperguyinohio]

I have a 2003 GMC Safari, I have replaced the Heater core, which was leaking,...Thermostat, which was running cool, Applied vacuum to the Heat control valve, that was missing...need to know how the heater control unit is supposed to work to make sure mine, and my junk yard replacement are not bad....Also was wondering if there is an electronically controlled Blend door or something I am missing

All help is appreciated and Thanks in advance

[redfury]

The heater control valve should have NO vacuum applied to it when you want heat. The control head sends vacuum to it when it wants it shut off. The default setting if you disconnected vacuum from the control head would be full heat at the defrost setting.

And yes, there is an electrically operated blend door. If you look on the passenger side of the van, look straight up the foot well next to the doghouse. It's triangular shaped with a silver circle with a notch cut through it. If you operate the heat level control from cold to hot, you should see it rotate. If it doesn't, you can remove it and reset it manually by taking it apart. It has limit switches to prevent the motors from over running the gears, but I've seen them lock up and bind for some unknown reason. I dealt with this with a similar year Silverado. If you reset it and didn't crank the heat all the way ( like 7/8ths ) it wouldn't bind. A touch further and it would over run the motor and bind up the gears. However, that should run the heat full blast if it's stuck full open.

this is what you'll be looking for.

This is what the inside looks like minus the gears.

[redfury]

The blue gear is what you set the limits left and right by. Likely I was getting the upper limit to close to binding when I was installing it thinking back on it.

[chevymaher]

LeAnn had a issue with that door opener on hers. Gears were bad if I remember correctly.

[redfury]

nice thing is, you can disconnect the electrical and just set it to the setting you want to keep it at for now, but it requires opening the unit up and changing the position manually ( you can't just turn it with the slot on the outside..trust me, I tried ).

[Leeann_93]

Yep, on mine the big gear cracked and jammed the works. No air out of the dash vents whatsoever.



You have to remove the doghouse and it's up against the heater core/blower housing on the passenger side.

[paperguyinohio]

I have an update....and a new issue... Replaced the heat control valve..amable to actually get heat from all vents as selected. the new problem is it really is only "heat" when i am reving the motor or driving... at idle it is cool to luke warm at best...dont think it is blend door as the temperature control works..cooler hotter...but again the air is only really warm at increased rpm... and I can actually hear fluid dumping into the heater core if i throttle it up... could it be a bad radiator cap..not bulding enough pressure???... any ideas?

Again all help is appreciated and Thanks in advance

[chevymaher]

Sounds like air bubbles in the system.
Water control valve still there?

[redfury]

That sounds like you have the heater control valve vacuum hose connected to the wrong port. Disconnect the heater control valve vacuum hose, you'll have heat all the time. If vacuum is applied to the control valve, it will be closed. The correct connection for the control valve is to have only the heater control valve connected to the lower port of the two that come from the firewall. The rest of the vacuum lines should be connected to the upper port.

[jbee]

I am having the same kind of problems with my 90 Safari. It does eventually get warm(ish), but it takes forever. Of course, the colder it gets--and it does get seriously cold here in northern Utah-the longer it takes. How do any of these ideas relate to my Safari?

[chevymaher]

Take the water control valve out. Have heat like a 60's chev then. Put in a ball valve turn the water off in the summer.

[paperguyinohio]

Is the water control valve same as heat control valve..?

[chevymaher]

He is checking the air blend door control as LeAnn suggested now.

[redfury]

Is the water control valve same as heat control valve..?

No, the water control valve is the valve part of the cooling system. The heat control is the blend door, which is the electronic control we posted pictures of. The water control valve is the vacuum controlled valve connected to the heater lines.

[dobaroy]

On our '03 Safari we have good heat coming out the front but we have cold air coming out the rear and do not have a clue where to start looking. Also the lines going to the rear heater core look like they need to be replaced, has anybody ever done this with rubber hose? Any ideas would be welcome.

[redfury]

The rear heat is controlled by an electronic switch that allows vacuum to pull on the valve beneath it. It is located by the firewall beneath the vacuum line junction. You can bypass the vacuum switch so it pulls vacuum on the valve full time. If that doesn't get you rear heat, then you may have a clogged valve if regular antifreeze was ever added to the old Dex cool.

[dobaroy]

Thanks for the reply. Is that the valve at the rear of hoses, just before they go into the heater core?