1999 Chevy S-10 No heat from any of the vent in my truck

Tiny
NORAD22
  • MEMBER
  • 1999 CHEVROLET S-10
  • 4 CYL
  • 2WD
  • AUTOMATIC
  • 130,000 MILES
My 99 S-10 stopped producing hot air from any of the vents when heat control knob is selected to full heat. So I put it on defrost and have selector knobe on cold. I hear the A/C come on and it blowes cold air, then I move selector knobe to full hot and hear a change in air flow to the windshield but no hot air. Disasibled the front part of the dash and looked at the back side of the air selector switches and all of a sudden hot air. This only worked for a few days, right back to cold air. I also noticed a few more days later that the coolent tempreature was lower than normal. So did a complete flush and cleaning of the system with the defrons on and full heat. Also replaced the thermastat as well. Still no heat so again I took the front part of the dash apart and looked at the slector switches and also disconnected the plug to the heat control knobe to see if there were any kind of discolorations. No discolorations, reconnected every thing and my heat is working again. Now three days after I did that I have no heat again. I have also checked both the return line and inlite line to the heater core and both of them are very hot. After I perforned the flush my tempreature gage is still reading low so I am thinking that the tempreature sending sensor is bad. How ever I need to know why I get no heat from any of the vents when I select heat. All the vent doors behind the dash close and open like they are suppost to how ever I have not check the door for the air to flow over the hearter core. Dont know where that is at behind the dash. Please help me, kind of hard to drive when the windshiled will not defrost.
Do you
have the same problem?
Yes
No
Thursday, October 14th, 2010 AT 5:08 PM

5 Replies

Tiny
DENNYP
  • EXPERT
Here is a diagnostic chart for you to try.(The hyperlinks won't work)

Temperature Control Inoperative
Step
Action
Value(s)
Yes
No

1
Was the HVAC Blower Controls System Check performed?
--
Go to Step 2
Go to HVAC Blower Controls System Check

2
Inspect the HVAC I fuse 21.

Is the fuse open?
--
Go to Step 20
Go to Step 3

3
Disconnect the air temperature valve sensor.
Turn the ignition switch to the RUN position.
Move the headlamp switch to the PARK position.
Using the J 35616-A, connect a J 39200 Digital Multimeter (DMM) between cavity 8 (CKT 733) of the air temperature valve motor connector and ground.
Move the temperature control knob from the HOT position to the COLD position.
Does the voltage vary smoothly and continuously within the specified range?
0-12 V
Go to Step 4
Go to Step 9

4
Using the J 35616-A, connect a J 39200 DMM between cavity 10 (CKT 341) of the air temperature valve motor connector and ground.

Does the voltage equal the specified value?
B+
Go to Step 5
Go to Step 7

5
Using the J 35616-A, connect a J 39200 DMM between cavity 10 (CKT 341) and cavity 7 (CKT 1850) of the air temperature valve motor connector.

Does the voltage equal the specified value?
B+
Go to Step 6
Go to Step 8

6
Replace the air temperature valve motor. Refer to Temperature Actuator Replacement.

Is the repair complete?
--
Go to HVAC Blower Controls System Check
--

7
Locate and repair the open or high resistance in CKT 341 between the IP fuse block HVAC I fuse 21 and air temperature valve motor.

Is the repair complete?
--
Go to HVAC Blower Controls System Check
--

8
Locate and repair the open or high resistance in CKT 1850 between the air temperature valve motor and G200.

Is the repair complete?
--
Go to HVAC Blower Controls System Check
--

9
Did the voltage remain at or near the specified value regardless of the temperature control knob position?
B+
Go to Step 10
Go to Step 15

10
Disconnect the heater controller/heater and A/C controller connector C3.
Using the J 39200 DMM, backprobe the jumpers at C3 terminal A (CKT 341) to terminal C (CKT 1050).
Turn the ignition switch to the RUN position.
Move the headlamp switch to the PARK position.
Measure the voltage drop.
Does the voltage equal the specified value?
B+
Go to Step 11
Go to Step 12

11
Replace the heater controller/heater and A/C controller. Refer to Control Assembly Replacement.

Is the repair complete?
--
Go to HVAC Blower Controls System Check
--

12
Move the headlamp switch to the OFF position.

Does the voltage equal the specified value?
B+
Go to Step 13
Go to Step 14

13
Locate and repair the high resistance in CKT 1050 between splice pack SP203 and G203.

Is the repair complete?
--
Go to HVAC Blower Controls System Check
--

14
Locate and repair the open or high resistance in CKT 1050 between the heater controller/heater and A/C controller connector C3 terminal C and splice pack SP203.

Is the repair complete?
--
Go to HVAC Blower Controls System Check
--

15
Did the voltage remain at or near the specified value regardless of the temperature control knob position?
0 V
Go to Step 16
Go to Step 10

16
Disconnect the heater controller/heater and A/C controller connector C3.
Using the J 35616-A, construct jumper leads in order to connect all of the connector C3 cavities to the appropriate terminals at the controller.
Using the J 39200 DMM, backprobe the jumper at C3 terminal B (CKT 733) to ground.
Turn the ignition switch to the RUN position.
Move the headlamp switch to the PARK position.
Move the temperature control knob from the HOT position to the COLD position.
Does the voltage vary smoothly and continuously within the specified range?
0-12 V
Go to Step 17
Go to Step 18

17
Repair the open or high resistance in CKT 733 between the heater controller/heater and A/C controller and the air temperature valve sensor.

Is the repair complete?
--
Go to HVAC Blower Controls System Check
--

18
Using the J 39200, backprobe at the heater controller/heater and A/C controller connector C3 terminal A and terminal C in order to measure the voltage drop.

Does the voltage equal the specified value?
B+
Go to Step 23
Go to Step 19

19
Using the J 39200, backprobe at the heater controller/heater and A/C controller connector C3 terminal A and ground in order to measure the voltage drop.

Does the voltage equal the specified value?
B+
Go to Step 11
Go to Step 7

20
Using the J 39200 DMM, probe the HVAC I fuse 21 test points.

Does the J 39200 DMM display the specified value at both test points?
B+
Go to Step 21
Go to Step 22

21
Locate and repair the short to ground in CKT 341 between the IP fuse block and the heater controller/heater and A/C controller connector C3 terminal A.

Is the repair complete?
--
Go to HVAC Blower Controls System Check
--

22
Locate and repair the open in CKT 300 between the IP fuse block and the ignition switch. Refer to Power Distribution Schematics in Wiring Systems.

Is the repair complete?
--
Go to HVAC Blower Controls System Check
--

23
Disconnect the jumper at the heater controller/heater and A/C controller connector C3 terminal B. Do not disconnect the jumper from the controller.
Measure the voltage at terminal B of the controller at the disconnected end of the jumper.
Disconnect the air temperature valve sensor.
Move the temperature control from the HOT position to the COLD position.
Does the voltage vary smoothly and continuously within the specified range?
0-12 V
Go to Step 24
Go to Step 11

24
Repair the short to ground in CKT 733 between the heater controller/heater and A/C controller connector C3 terminal B and the air temperature valve sensor.

Is the repair complete?
--
Go to HVAC Blower Controls System Check
Was this
answer
helpful?
Yes
No
Thursday, October 14th, 2010 AT 7:31 PM
Tiny
NORAD22
  • MEMBER
At step three you lost me completely. I havent a clue on what you are talking about and where any of these parts are located at. All I know is that the blower does work A/C works greate. The will work after I have removed the front part of the dash but a couple of days later it stops.
Was this
answer
helpful?
Yes
No
Friday, October 15th, 2010 AT 10:50 PM
Tiny
DENNYP
  • EXPERT
Do you have a DVOM? (Digital volt ohm meter)
Do you know how to measure for voltage and resistance?
(I need to get an idea of what level electrical knowledge you are at. This helps me to determine how in depth to get on the instructions)
Let me know which components you need help locating.
Was this
answer
helpful?
Yes
No
Saturday, October 16th, 2010 AT 9:06 AM
Tiny
NORAD22
  • MEMBER
Yes I do have one and yes I know how to use it. I did check the resistor for the heat/cold selector knob and that seems to work. I get a veriance of.5v to 3V it fluxuates some but there is a noticeble change when the knob is moved. I also took off the supply and return lines off of the heater core and hooked up 10psi air to it to flush it out to see if by any chance there was something in there. I did not see any thing come out other than clean fluid. Good this is I can not see any build up of any kind on the hoses or on the heater core.
Was this
answer
helpful?
Yes
No
Sunday, October 17th, 2010 AT 11:23 PM
Tiny
DENNYP
  • EXPERT
First, check to see if the temp door actuator moves when you turn the temp control knob. You should be able to see the motor shaft turn.
It is located behind the glovebox, on top of the HVAC box.
It is number 1 in the pic.


http://www.2carpros.com/forum/automotive_pictures/102900_393159_1.jpg

Was this
answer
helpful?
Yes
No
Monday, October 18th, 2010 AT 7:52 AM

Please login or register to post a reply.

Recommended Guides