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No heat 99 silverado with 5.3L

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New User

Dec 5, 2006, 6:27 AM

Post #1 of 7 (8924 views)
  post locked   No heat 99 silverado with 5.3L  

Hi all hope one can help with my heat problem I have a 99 sliverado with the 5.3 in it..Just as we were coming out of last winter I noticed that the heat would sometimes come on and sometimes not so then summer comes and I forget about it, at the end of the summer I noticed a mist coming form the vent when the ac was on so I figure ok heater core..Well I replaced the heater core (what a job) still no heat. I have checked to see if the lines (radiator and heatercore) were vacum locked And it doesnt appear they are. I took off the return hose (top of radiator)got the fluid flowing ,also ran it and got it circulating with the pressure cap loose no more bubbles and gurggling noise and finally parked it on a hill so the passenger side was way up and ran it with the pressure cap off. So after that guess what still no heat...So i changed the t-stat..Still nothing..all controls seem to work floor,mid ,defrost ect..I havent recharged the a/c system yet would that make a difference?.As for the middle knob that switchs from cold to hot on the console When I turn it left to right and vice versa i dont hear any noise (someone said to listen) but on my friends chevy 2002 silverado you cant hear any noise when he switchs it either and he has heat ...At a loss now...and looking out side the window this morning its all white outside soo burrrr. lol
Thanks for any help...

(This post was edited by Outdoorsman on Dec 5, 2006, 6:28 AM)

Tom Greenleaf
Ultimate Carjunky / Moderator
Tom Greenleaf profile image

Dec 5, 2006, 10:07 AM

Post #2 of 7 (8908 views)
  post locked   Re: No heat 99 silverado with 5.3L  

Probably the temp diverter door or the control of it.

The A/C would not cause lack of heat but you should at least vac and pre charge it or it may croak by when you want it to work again, T

New User

Dec 5, 2006, 8:52 PM

Post #3 of 7 (8904 views)
  post locked   Re: No heat 99 silverado with 5.3L  

Was afraid you'd say that lol...Thanks for the help...I'll try to trouble shoot the switch and see if thats it..Hope that is all it is...I should have checked when I had it all apart the first time...But who knew....Thanks again

steve01832 profile image

Dec 6, 2006, 3:45 AM

Post #4 of 7 (8900 views)
  post locked   Re: No heat 99 silverado with 5.3L  

Sorry to say this, but if you had a mist coming out of the vents with the A/C on, chances are the evaporator core let go. It is located inside the heater and a/c module. Rule of thumb, if you have to pull the whole module out to do one core, it is advisable to replace both.


New User

Dec 6, 2006, 6:29 AM

Post #5 of 7 (8897 views)
  post locked   Re: No heat 99 silverado with 5.3L  

When I changed the heater core the was a very small amount of anti-freeze in the box that the heater core sits in...Any way to check the evaparator core with out having to take the whole thing apart again?.When it first started to go (the heat) It almost seemed like there was a climate control issue but I dont have that on this model silverado 1500 LS...Just standard knobs...When it was really cold outside like 0 to 20 the heat would come on, but a few days when the sun was up and shinning and the temp got to be around 30 or so the heat wouldnt work at all..Blower and such were fine just blowing cold air...The ac worked all summer till around sept then I noticed mist coming out of the vents and the smell of anti-freeze in the air..would also get all over the winshield when I had to defrost it say for it fogging up when it was raining out...Also at this point the coolent was dropping on a regular basis. Thanks again..

(This post was edited by Outdoorsman on Dec 6, 2006, 6:32 AM)

New User

Sep 17, 2011, 12:15 PM

Post #6 of 7 (5663 views)
  post locked   Re: No heat 99 silverado with 5.3L  

Hi I read your post and have the same problem with no heat
just wondering if you got it fixed...and what was the problem ,

Hammer Time
Ultimate Carjunky / Moderator
Hammer Time profile image

Sep 17, 2011, 12:40 PM

Post #7 of 7 (5659 views)
  post locked   Re: No heat 99 silverado with 5.3L  

This thread is 5 years old. Please look at the dates before posting and if you have a question or problem, please start a new question of your own.


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