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84 G20 with low/no heat #728026
September 19th 2017 10:27 pm
September 19th 2017 10:27 pm
Joined: Sep 2017
Posts: 25
MN
JAGI410 Offline OP
newbie
JAGI410  Offline OP
newbie
Joined: Sep 2017
Posts: 25
MN
Winter is coming and I’m new to these older vans. Here’s a weird one. When on “heat” mode, low/no air comes from the vents regardless of fan speed.

-AC blows cold and responds to fan speed
-Vent blows warm and responds to fan speed on “vent” mode
-Defrost works well
-van runs cool on temp gauge (never over 1/4 up)
-heater hoses hot
-heater core replaced/system flushed a year ago (previous owner)
-upper radiator hose cool/empty feeling
-coolant topped off
-new radiator cap
-recent water pump (previous owner)

I’m thinking thermostat, but shouldn’t the vents be blowing air at me in heat mode?


Jason
1984 Chevy G20
Re: 84 G20 with low/no heat [Re: JAGI410] #728031
September 19th 2017 10:39 pm
September 19th 2017 10:39 pm
Joined: Sep 2005
Posts: 8,365
Georgia, USA
CatFish Offline
carpal tunnel
CatFish  Offline
carpal tunnel
Joined: Sep 2005
Posts: 8,365
Georgia, USA
In "heat" setting you will only get air flow from the floor/under dash openings.
To get warm or hot air from the dash vents you would need to swap to vent and push the temp control to hot.

Is there air flow from the underdash/ floor area in "heat"?

Last edited by CatFish; September 19th 2017 10:41 pm.

They can have my fried bologna sandwich when they pry it from my cold dead hands.
Re: 84 G20 with low/no heat [Re: JAGI410] #728039
September 20th 2017 9:11 am
September 20th 2017 9:11 am
Joined: Sep 2017
Posts: 25
MN
JAGI410 Offline OP
newbie
JAGI410  Offline OP
newbie
Joined: Sep 2017
Posts: 25
MN
Thanks for the quick response Catfish! That's helpful to know that air doesn't come from the upper vents in "heat" mode. Yes I believe there is air flow coming from below in heat mode. So now it's just a matter of figuring out why the van runs cold. I will swap the thermostat this weekend.


Jason
1984 Chevy G20
Re: 84 G20 with low/no heat [Re: JAGI410] #728043
September 20th 2017 10:46 am
September 20th 2017 10:46 am
Joined: Sep 2005
Posts: 8,365
Georgia, USA
CatFish Offline
carpal tunnel
CatFish  Offline
carpal tunnel
Joined: Sep 2005
Posts: 8,365
Georgia, USA
Hope it helped.
We currently have three GM vans. All of which are "cold natured" as the saying goes. They all seem to take their sweet time warming up from a cold start even with a proper working T-stat.


They can have my fried bologna sandwich when they pry it from my cold dead hands.
Re: 84 G20 with low/no heat [Re: JAGI410] #728048
September 20th 2017 11:37 am
September 20th 2017 11:37 am
Joined: Aug 2001
Posts: 11,652
Fircrest, WA
Reed Offline
Maniac
Reed  Offline
Maniac
Joined: Aug 2001
Posts: 11,652
Fircrest, WA
I know pretty much nothing about Chevy vans or technology, but I have a few generic suggestions. First, if your van has a clutch fan, check if the clutch has failed in the "on" mode and is making the fan spin at all times. This can cool the radiator fluid too much and make warmup times longer. Second, reverse flush your heater core. You will be surprised the gunk that can build up in there. Third, verify the temperature blend door is moving properly and the seals around the door are in good condition.


Windows- they're what make a van worth owning!
Re: 84 G20 with low/no heat [Re: JAGI410] #728097
September 21st 2017 9:09 pm
September 21st 2017 9:09 pm
Joined: Sep 2017
Posts: 25
MN
JAGI410 Offline OP
newbie
JAGI410  Offline OP
newbie
Joined: Sep 2017
Posts: 25
MN
Good suggestion on the fan clutch, but that is not the case here. I drove it a little longer today and the upper radiator hose got hot, so the thermostat is certainly working. Warm air comes out strong from lower vents, but it’s not as hot as every other car I’ve owned. Perhaps it really is just cold blooded. A Cardboard radiator blocker might be necessary to survive a MN winter!


Jason
1984 Chevy G20
Re: 84 G20 with low/no heat [Re: JAGI410] #728173
September 24th 2017 11:19 pm
September 24th 2017 11:19 pm
Joined: Sep 2016
Posts: 33
Illinois
V
Vanereal_Disease Offline
newbie
Vanereal_Disease  Offline
newbie
V
Joined: Sep 2016
Posts: 33
Illinois
Maybe an air bubble in the heater core?

Are both hoses to the heater core hot?

Or.... get one of those fancy laser temperature things and make sure the whole core is getting hot and not just one path through it.

Re: 84 G20 with low/no heat [Re: JAGI410] #730592
December 11th 2017 1:48 pm
December 11th 2017 1:48 pm
Joined: Jun 2017
Posts: 7
VAN BC
T
tyteric Offline
stranger
tyteric  Offline
stranger
T
Joined: Jun 2017
Posts: 7
VAN BC
on my '89 G30 there was basically no heat coming out of the vents. pulled the blower van housing off and could feel the core getting hot. Turned out the PO didn't install a thermostat when they replaced the heater core. The temp gauge was also sitting flat the whole time so replaced the sending unit and installed a new thermostat and everything is working fine now.


2005 ASTRO CARGO LIFTED AWD
1989 G30 TBI CARGO with TMW
Re: 84 G20 with low/no heat [Re: JAGI410] #733315
February 21st 2018 1:53 pm
February 21st 2018 1:53 pm
Joined: Sep 2017
Posts: 25
MN
JAGI410 Offline OP
newbie
JAGI410  Offline OP
newbie
Joined: Sep 2017
Posts: 25
MN
Updating this thread while I'm here! I put cardboard in front of the radiator (but behind the grille because she's classy) and it does help. It takes quite a long drive to get hot air out of it though, I rarely bother with the heat since most of my trips are 10 minutes or less this time of year. I still plan on changing thermostat in the spring. It's too damn cold for wrenchin' currently.


Jason
1984 Chevy G20
Re: 84 G20 with low/no heat [Re: JAGI410] #733342
February 21st 2018 11:31 pm
February 21st 2018 11:31 pm
Joined: Mar 2016
Posts: 316
Tucson,Az.
H
Hasan Ben Sobar Offline
enthusiast
Hasan Ben Sobar  Offline
enthusiast
H
Joined: Mar 2016
Posts: 316
Tucson,Az.
There should be a "mixer" door that regulates the mixture of hot/cold air to the vents. Also , does the van have a shut off valve for the heater core? Does it have full range of motion?


Tucson-it's a dry heat...like an oven
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