Hello,
New to forum looking for some help please.
1999 Blazer LT 4 door 4WD.
Several years ago heat stopped working did some research and most popular problem was with blend door actuator. Replaced that item yesterday, what a pain getting way back up in there. Mine is the Automatic temp actuator not the manual temp one. Replacing that did not fix problem. I could move the door manually when I had the old actuator out and can hear the door moving with new actuator installed. I took old actuator apart and gears not cracked all the way through like I expected, but replaced it anyway. when temp dial is turned to heat, there is no heat.


Any Idea what else could be wrong?
Thank you for any help you may be able to give.

 

Are the heater core hoses similar in temperature? If not, you could have a restricted/plugged heater core.

 

Thank you for your reply.
Went for a drive up to operating temperature.
Both heater core hoses are same temp, not hot, feels like same temperature as lower radiator hose. Upper radiator hose is definitely hot in comparison.


Any other ideas?

 

Thermostat might be stuck open.

 

Checked the coolant temp gauge after driving and engine nice and warmed-up. This will help in determining if the thermostat is stuck open. Had mine do this, but it set the CEL to let me know.

Also you could try cleaning the heater core...rather messy, but might help. Just be sure to use GENTLE water pressure to back flush the heater core.

Good luck.

 

St3v3
Thank you for your reply.
Tried to do this, but could not get the two nuts off that hold the piece that the thermostat sits under. tried liquid wrench penetrant but could not get them to budge. was afraid to use too much force and shear something off.
I did start the vehicle with the rad cap off and felt the fluid with my finger. it warmed up as the temp gauge increased and the fluid seemed to expand in volume. It spilled out of the radiator. when the temp gauge hit operating temp the coolant level dropped and stopped flowing out and then started to raise again and then dropped again. I don't know much about this but am hoping that I am describing what a normal functioning thermostat is supposed to do. Can anyone confirm this sounds correct and is what I should have experienced?

 

LannyL81
Thank you for your reply.
I will try that next. I did get the clamps off one line yesterday, but could not get the hose to budge was running out of daylight and stopped. Any suggestions on how to get a 17 year old hose loose from the heater core outlet without breaking something. Also I can see one of the hoses comes off the water pump maybe? and the other looks like it goes into the engine? which hose do I flush to "back flush", I don't know the proper flow direction.

 

My 2000 trailblazer I just got was doing the same thing just flushed and added blue devil rad flush It cleand out heater core with having to remove it works great now heater is hot

 

Butch,
Thank you for your reply.


I was able to pull the heater core hoses off today, bought hose pliers from harbor freight, worked awesome. Went to Lowes and bought vinyl hoses and garden hose adaptors for flushing the heater core. 5/8"ID costs 49 cents per foot and 3/4"ID braided $1.79 per foot for anyone else who wants to do this. need three connectors. one male to garden hose that attaches to 5/8" and then a female / female to connect garden hose to 7/8". About $20 in parts.


Flushed the heater core and got only a tiny amount of sediment. I flushed reverse direction of normal flow then forward then reverse again. Because I only got a little sediment I started thinking air bubble. I decided to fill the heater core with 50/50 antifreeze then fill the heater core hoses also. I filled the one to the water pump till full then attached to heater core. I filled the one to the engine block until it came flowing out of the heater core then attached that hose.


Went for a drive and after reaching operating temperature switched to heat and it WORKED. First time I've had heat in several years. Wish I had looked into this years ago.


Thank you all for the advice and I hope this thread helps anyone else having the same problem I did.

 

Today I also solved a No Heat issue by both forward and back flushing the heater core. I tried just back flushing last week and to no avail. Today I tried the forward and backward method (about 6 times each direction) and now heat works like a champ !