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Heater problems ('91 Sub)

G

GR

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Dec 7, 2005
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Location
Peyton, CO
My "newly" acquired '91 Suburban (5.7L) blows warm air from the heater and still blows some through the vents when set to "HEAT".
The vacuum control to the valve in the heater core hose isn't working but hot radiator fluid still appears to be reaching the heater core because both hoses (to and from) are warm.
So now the questions...
Should the valve be actuated or not when set to "HEAT"?
No vacuum is present at this valve no matter what the A/C controls are set to. I hear the other vacuum actuators move for the other settings but nothing at that valve.
What temperature thermostat should this truck have?
My temp. gauge on the dash stays below 210 all the time. I'm thinking a new thermostat is in order to heat things up.

Also, my A/C compressor won't kick on at any setting of the controls.

Any other suggestions/comments/help/guidance/opinions?

Thanks
 
The vacuum coolant valve should only open when you turn on the rear heat (and there will not be a vacuum coolant valve unless you have the rear heat option). Coolant is always flowing through the front heater core.

The a/c system has a low pressure cutoff switch that will prevent the compressor from running when the system is low on refrigerant. Time for a recharge.
 
HarryH3 said:
Coolant is always flowing through the front heater core.

.
Click to expand...
I disagree. There will always be coolant in it, and the hoses should always be warm from the engine coolant heat. But it does not always flow through the core. It only flows when the hot water valve is open.

If the hot water valve is vac actuated, put a hand vac pump on it and see if it holds vac. Im not sure if it needs constant or temporary vacuum. If you put direct vacuum on it and it works, there is something wrong upstream.
 
Leper said:
I disagree. There will always be coolant in it, and the hoses should always be warm from the engine coolant heat. But it does not always flow through the core. It only flows when the hot water valve is open.

If the hot water valve is vac actuated, put a hand vac pump on it and see if it holds vac. Im not sure if it needs constant or temporary vacuum. If you put direct vacuum on it and it works, there is something wrong upstream.
Click to expand...
Step outside with your digital camera and look under the hood of your rig. Please upload pictures of your hot water valve. :wink1: GM didn't use 'em on our rigs, other than with the rear heat option. On rigs with the rear heat option, only coolant to the rear heater is controlled by the hot water valve. Coolant is always flowing in the front core.
 
89GMCSuburban said:
I agree with Harry...I don't have a shut off on my sub...and it don't have rear heat.
Click to expand...
I'll bet that you're wishin' it did, now that you live in Colorado! :wink1:

It actually isn't that difficult to install, if you can find a donor Burb. :)
 
pics

I'll take some pics tomorrow and post them.
The valve I have is on one of the heater hoses from the block to the heater core. Doesn't go anywhere else, not a tee.
This Sub was ordered as an unfinished chassis and sent to VanWorks in Ft. Collins for finishing. There is an overhead unit with vents in the back with a switch under the dash (to the left of the steering column) for fan control. Haven't gotten that to work yet either.
Are the lines under the right side of the truck going to the back A/C lines or could they be heater lines? I guess I could go trace them back to where they go in the engine compartment.
 
Someone added that valve at some point in its life. GM didn't ship 'em with a hot water valve. I added a manual one to my '75 K5 to keep the summertime air vent temps a bit cooler when I lived in Houston. It worked. :)

The stock rear heater in burbs of that era was mounted on the floor, just inside the rear doors, to the passenger side. The ceiling unit is a/c only. They integrated them into one unit when the newer body style came out in '92.

How far "east" are you? Anywhere close to Colorado Springs?

Oh yeah, I think that the conversion company must have installed their own control for the rear a/c, as the factory put the rear fan control in the sheetmetal of the dash, just to the right of the ash tray.
 
I just updated my location.
Peyton but I work in the Springs a couple a days a week.

Do you think VanWorks added the valve for some reason? The vacuum line that controls it looks to be factory in its routing and connections.
 
They probably added it to make sure that the a/c would blow cold. GM uses trap doors under the dash to control the temp coming out of the dash. As the seals on the doors age, they let some of the heat leak into the a/c airstream. :( It's possible that they added the entire a/c system. There are some aftermarket a/c systems that look very much like the stock stuff until you look really closely.

If you want, I could take a look at if for ya on one of your trips to the city. ;)
 
HarryH3 said:
Step outside with your digital camera and look under the hood of your rig. Please upload pictures of your hot water valve. :wink1: GM didn't use 'em on our rigs, other than with the rear heat option. On rigs with the rear heat option, only coolant to the rear heater is controlled by the hot water valve. Coolant is always flowing in the front core.
Click to expand...

It will be a few days before I can show you a pic. My camera on my phone sucks, but the valve is there. My truck did not come from the factory with a/c. It doesn't even have dash vents. That may have something to do with it. Or it may have been installed by the military, my truck used to be an airforce security patrol vehicle.
 
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