No Heat (front or rear)

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Klympt

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(Sorry if this is all over the place. It's been very confusing as to why this won't work.)
Recently picked up a 2003 Yukon XL SLT with the fancy digital dual zone auto control head.
Back story: While initially going through it, found that the water pump was leaking from the weep hole. Replaced the water pump, thermostat (186 deg F), and upper and lower hoses for good measure. One week later, radiator blows out on a hot day (due to possibly sitting with too much water over the winter and freezing). Did a hose flush of the heater cores (forward and reverse) as well as the engine, replaced the radiator, and did a vacuum fill to ensure no air in the system. Replaced the buzzing cab temp sensor above the driver seat as well.
Fast forward and it gets real cold outside, and now I discover there is no heat from front or rear. I found a bad blend door actuator on the rear (did not move when I changed settings) and manually set it to full heat before putting the actuator back in place and unplugging it so it would not move. Still no heat.
I noticed the temp on the mirror was reading in the 90's when it was in the 30's and the mirror would restart at random several times per minute. I replaced the ambient temp sensor in the grill, the temp continued to show in the 90's, but then began reading right after about a half an hour of driving (in town and on highway). Still no heat.
Items replaced:
Water pump
Thermostat
Upper and Lower radiator hoses
Cab temp sensor
Outside ambient temp sensor

Verified no clogs in heater input hose, heater output hose, the hose going to the pipe on the intake, the pipe itself (was clogged but cleaned out). At temp with thermostat open (198-205 as read from the OBD2 port), input hose is hot, output hose is not cold but not as hot as input side.
All actuators appear to cycle when doing the HVAC fuse-pull-relearn (air cycles through defrost/face/floor) and recirc works as the sound increases as expected.
Not sure where to go from here. Is there a way to manually jump the plug for the climate control unit to force it to full heat? Another way to test that I am missing?
(Full disclosure - if there is a way to manually set this thing to full heat for right now, that would be great. I can worry about fixing the rest of it later when money isn't so tight...)
 

BaMaDuDe87

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Aftermarket radiator?

There is a line that goes from the radiator to the surge tank. On the stock radiator, there is a reducer here. Seems most if not all aftermarket radiators do not have this. Put a hose clamp on this hose and “reduce” it a good bit.


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Doubeleive

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are you sure you have the rear door set for heat?
for the front the hot/cold blend actuator is the one closest to the blower motor under the glove box passenger side kick panel, you should be able to use the same method for that if it is not working properly.
 

Flingflanger

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You know that actuator that's in the middle of your dash that's almost impossible to get to? That's your problem. And or the wiring harness going to it. Sometimes the wiring harness rubs against a sharp edge and that causes problems. Sometimes its the actuator. Sometimes its both! And I think the wiring harness also handles the ambient temperature sensor.

There's where I'd go after all you've done.
 

Doubeleive

Wes
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You know that actuator that's in the middle of your dash that's almost impossible to get to? That's your problem. And or the wiring harness going to it. Sometimes the wiring harness rubs against a sharp edge and that causes problems. Sometimes its the actuator. Sometimes its both! And I think the wiring harness also handles the ambient temperature sensor.

There's where I'd go after all you've done.
that actuator is for defrost, the hot/cold actuator is situated right at the blower motor output front and rear.
 

Joseph Garcia

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Welcome to the Forum from NH.

Lots of knowledgeable folks here who freely share their knowledge, experiences, and perspectives. Knowledge is power.

I hope that you will become a participating member in the Forum's discussions.

Pics, please.

I'm sorry that I cannot personally assist you with this issue, but it is an issue that have been discussed several times before here on the Forum. Some of the folks here have already offered suggestions, and other folks will chime in.
 

Fless

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Aftermarket radiator?

There is a line that goes from the radiator to the surge tank. On the stock radiator, there is a reducer here. Seems most if not all aftermarket radiators do not have this. Put a hose clamp on this hose and “reduce” it a good bit.


Sent from my iPhone using Tapatalk

He said the OBD reading was indicating a full engine warmup, although that could be reporting incorrectly.
 

Doubeleive

Wes
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Just went through this myself but ok. you do you. I'm not here to argue.
me neither, so just to clarify, if the actuator you are talking about was connected to a part like this in the photo below then that had nothing to do with hot or cold, that one is for which direction the air flows only
defrost.JPG
 
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Klympt

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Sorry about being so late checking back in.
It looks like I am dealing with multiple issues at once, but I did get heat going.
First, did another forward and reverse flush of the heater cores at the firewall. I got some more debris out, leading me to believe that the heater core(s) are beginning to deteriorate, but they arent leaking yet.
Second, when I pulled the cover off the bottom of the front heater box, the plug for the blend door actuator (controls heat, located passenger side right above the transmission hump) came off, which means it had an intermittent connection. I verified it works by pluggung it back in and doing a fuse pull relearn and watching ot cycle. I then unplugged it, manually set the blend door to heat and reinstalled it but left it unplugged. No need for cold air when it is below 32 degrees.
Lastly, I unplugged, manually set to heat, and reinstalled the rear actuator and left it unplugged.
I have heat for now, but will probably pick this up again around spring time.
Thank you all for your help.
 

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