99 GMC Jimmy HEATER

CJLOTTI

MEMBER
1999 GMC JIMMY
6 CYL
4WD
AUTOMATIC
107 MILES

I HAVE NO HEAT, DURING COOLING SYSTEM OVERHAUL I DISCONNECTED THE 2 HOSES GOING TO HEATER CORE IN FIREWALL LEFT SIDE. IT WAS BADLY CLOGGED. CLEANED IT OUT AND HAD GARDEN HOSE CONNECTED AND BLEW OUT DEBRIS OUT OF OTHER TIP, I HAD CLEAN WATER FULL FLOW IN AND OUT. ONCE RADIATOR WATER PUMP THERMOSTAT AND COOLANT REPLACE ALL IS GOOD WITH COOLING SYSTEM, BUT NO HEAT WHEN TURNED ON. BLOWER WORKS BUT NOT HEAT.

WHAT CAN BE WRONG HERE?

THANKS ALL FOR YOUR ADVICE!

5 Replies

FIXITMR

MECHANIC
9,990 POSTS

Are the hoses going in and out of core both hot when engine is at operating temp?

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Thursday, October 4th, 2018 AT 11:12 AM

BMRFIXIT

MECHANIC
19,053 POSTS

Idle engine for about 20 minutes until warm or until thermostat opens. Ensure coolant temperature is about 194°F (90°C).
Select vent mode. Move temperature lever to coldest temperature setting. Select high blower speed.
Air should exit instrument panel outlets and should be about the same temperature as outside air.
Move temperature lever to hottest temperature setting.
Air should get warmer if not open hood and check heater hoses if both hot
if not heater core is the problem and need to be flushed again and or replaced
if both hoses hot its blend door
let me know

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Thursday, October 4th, 2018 AT 11:12 AM

CJLOTTI

MEMBER
5 POSTS

Hi, thx for reply
yep both tubes and hoses connected to em are hot. No heat, blower works on fresh setting and recirculate setting, all vent settings blow air. No heat

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Thursday, October 4th, 2018 AT 11:12 AM

BMRFIXIT

MECHANIC
19,053 POSTS

Inside the truck under dash and on the HVAC box
check blend door actuator
Some but not all have temp control cable instead of actuator
check if have one and if its functional

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Thursday, October 4th, 2018 AT 11:12 AM

CJLOTTI

MEMBER
5 POSTS

Hey bmrfixit and fixitmr,
wow thanks a bunch for the 411 on this prob I have. I havnt checked truck do to rain in my area, and other things. But I sure do appriciate your responses, sure does help guys. I will post back to let ya know!
Thx again, and happy holidays!