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new here and need some help

M

mcbowler

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Hello all, I just joined this site, and I am looking for some help. I have a 1995 tahoe, and I have lost the heat, I have replaced the water pump, t-stat, heater core, and all I am getting is cold air, part of the core gets hot, but not all of it, I have even flushed it out. It is still cold here in Michigan, and I really need to get some heat, is there anyone that can give me some advise on this matter?
 
Welcome to The Truck Stop! Take some time to fill out your signature so everyone knows what you are driving. I moved your request to a section of the forum that should get you some help in short order.
 
:welcome8:
The 95s have a very failure prone control unit. It is a one year only. Just a little background.
Can you hear the electric actuator running when you change temp settings with the control?[best to do with the engine off, key on]. Can you hear the actuator motors running when you change modes[as in heat to defrost]? Have you checked all the fuses?
Another weak point in these trucks is a wire connector that is behind the glove compartment. It is a 2 wire connector with red and black wires only. The connector is under sized and will melt internally especially if the blower motor has gone bad and is drawing too much power. The control will do weird things when this connector is bad. The fix is to eliminate the connector completely with either a butte splice crimp connector or to solder and heat shrink tube the connection.
Another possibility is a actuator motor that stripped it's gears. You will hear it run but nothing changes.
Maybe the simplest thing is the heater core is plugged up.Both hoses should be hot with the engine warmed up. Coolant flows through the heater core all the time regardless of the control position. Some have had success simply back flushing the heater core with a garden hose. Check and see if the functions are working first and if both hoses get hot[both free]
 
It could be that the heater controls are not working that make the air actually go across the heater core. A damper has to move to allow that.

If the heater core isnt getting hot, have you made sure the heater hoses aren't clogged?

What temp is the truck running? The T-stat needs to open to circulate through the core.
 
"The T-stat needs to open to circulate through the core.":???::hihi: The radiator ,yes,heater core, no.:D
Good catch on the thermostat. The ONLY thermostat s that work in a 6.2 and 6.5 are AC Delco or Robertshaw. All other brands cause wild engine temperature swings.
 
btfarm said:
Not doubting you Barry but wouldn't the heater core be dead headed until the T-Stat opens just like the radiator? Or is there an open loop from the pump?
Click to expand...

If there wasn't flow to the heater core all the time you would have no heat at all untill the engine was completely up to temp. The thermostat only controls the flow to the radiator and in a 92-95 -6.5 it also controls the bypass. For the thermostat to control flow to the heater core the heater hose would have to be between the thermostat and radiator.
Back in the old days the flow to the heater core was controlled by a vacuum or cable actuated valve. Now, even on a 100 degree day the heater core is as hot as the coolant. The air flow across the heater core is controlled.
 
If water cannot flow between block and the radiator, how does it flow to heater core through the radiator? Our heater core hooks to the radaitor, no valve, in a lot of those systems heater core doesnt go to the radiator. A lot of radiators only have lower, upper and reservoir to them, ours also has the heater core.
 
me thinks your year has two of these. There would be one on each side of the tranny hump about 4 inches off the floor. Try swapping them from one side to the other. Me thinks you might get heat but possibly lose control of vent function. If this is the case one is shot. They are called heater blend / door actuator and are available from rockauto for 27.10 here is a pic
getimage.php
 
buddy said:
If water cannot flow between block and the radiator, how does it flow to heater core through the radiator? Our heater core hooks to the radaitor, no valve, in a lot of those systems heater core doesnt go to the radiator. A lot of radiators only have lower, upper and reservoir to them, ours also has the heater core.
Click to expand...

The coolant flows from the crossover[quick connect] to the heater core then dumps into the cold side of radiator. There would be no heat if it, somehow, could flow the other direction.
 
bk95td said:
The coolant flows from the crossover[quick connect] to the heater core then dumps into the cold side of radiator. There would be no heat if it, somehow, could flow the other direction.
Click to expand...

Is water moving in the radiator before the thermostat opens? That means when the heater core dumps into the cold side it has to be able to displace other water, otherwise it would just deadhead like BT said.
 
buddy said:
Is water moving in the radiator before the thermostat opens? That means when the heater core dumps into the cold side it has to be able to displace other water, otherwise it would just deadhead like BT said.
Click to expand...

Coolant is being drawn into the water pupmp from the lower rad hose.
From the water pump it goes into the block, heads,.....
Coolant then either sits in the heads and block until thermo stat opens and flows to rad upper hose OR flows thru the quick connect (as stated b4) into the heater core
from the heater core it ties into the lower rad hose going to the water pump.

So in basic until the thermo stat opens the coolant flows through the water pump, block, heads, and heater core only.
 
It is possible to air lock the heater core if your heater hoses are reversed.

bk95td said it. I have seen full heat in AC mode and no heat when my control head failed the 2nd time in my 1995 Yukon. Get used to this regular replacement part. As far as the wires burning up behind the glove box, all years suffer from this and I add a ground wire to the blower motor to a good ground to help.

Just in case you have a gas engine there will be a heater bypass valve below the AC accumulator (Silver can passenger side firewall.) that runs off vacuum. Damage to it's vac line will cause issues. So will control head issues affect this part. The valve itself can fail, but, you can see the valve work from the external silver lever.

If the core is not hot check the FUBAR design fitting on the crossover that feeds the heater core. GM has a plastic restriction in it and it may pick up debris and clog. Replace this fitting with a hose barb and use 3/4" hose to do away with this leak point. Careful on the fragile crossover and be aware the pot metal GM fitting may have to be beat out in chunks. The other way to fix this is a new o ring and remove the restriction. (If and only if the GM fitting isn't leaking.)

You should see the amount of coolant that goes through the heater core with a low output water pump vs. the high output water pumps. You will have to look in a 1993 year as you take the cap off and can see the heater core return just below the cap in the radiator tank. The heater picks up water from the engine crossover before the t-stat that is under pressure from the water pump and returns it to the cold side of the radiator that is on the suction side of the water pump. The thermostat being open could reduce the flow through the heater core. If the 'wrong' thermostat does not have a bypass block off 'valve' this could also cause low heater core flow.
 
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