Question about 1998 Chevrolet Astro

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1998 Chevy Astro: HVAC air flow control - cannot change flow with control, replaced vacuum line (dryrotted) to accumulator ball however, still no vacuum. Checked all the vacuum lines in dash - no kinks. Cannot find the source of vacuum for the system - by disconnecting lines land listening, there doesn't seem to be any.

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  • Jeffrey Turcotte
    Jeffrey Turcotte Sep 27, 2010

    There should be a vacuum line from the accumulator to the switch. Can you trace that line? Can you pull it off the accumulator to see if it is storing vacuum?

  • flyguy_dem Sep 27, 2010

    Dead On! I hadn't realized it, but, the the small, plastic, vacumm line, coming off by the PCV valve (just to the side of the throttle body), that goes over to the check valve by the A/C Accumulator, had actually broken in half. A couple of inches of rubber vacuum line attached to splice it and, the problem is fixed. Thanks for your help, I may have never seen it!

  • flyguy_dem Sep 27, 2010

    Dead On!...pointed me right to the issue and was fixed in minutes. Thanks....best support money I've ever spent.

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Carefully identify the vacuum line(s) attached to the intake manifold to look for a leak.Your problem is located where the rubber air inlet meets the engine throttle body. Look under this rubber inlet and you will find a black plastic vacuum line. It has a hole in it or is just falling apart. Replace this line from the intake manifold to the tee up by the A/C accumulator/dryer.
--------------------- If the fan motor works but the location of the airflow can not be changed, the blend door motors or vacuum solenoids must be checked for operation. Pull the glove compartment box out and the motors or solenoids will be visible. With the engine running, move the controls and watch for them to move. If they fail to swing the arm for the doors to open, check to see if they are getting power or vacuum. For power check with the circuit tester, and for vacuum simply pull the line off and check for vacuum problems. If there is no power and the fuses are good, then the control unit on the dash is bad. If there is no vacuum, check the vacuum source--a small vacuum line running through the firewall to the engine manifold or into the power brake vacuum booster.------------ The HVAC splitter operates on vacuum. The vacuum line from the intake manifold to the solenoid that operates the air diverters must be loose,cracked or kinked.You should be able to find the line from the front of the vehicle with the hood raised. It's a 1/8" black plastic line that travels from the intake manifold on the drivers side up forward to where the a/c unit is located. --------

Thanks. Keep updated for any more query. You can rate this solution and show your appreciation

Posted on Sep 27, 2010

  • raj somaiya
    raj somaiya Sep 27, 2010

    Thanks for the appreciation.

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I have a 2002 Chevy Impala the heat and air comes out all the vents at the same time can't direct it


After looking at the service info for the HVAC system for your vehicle , it sounds like your system lost vacuum somewhere ! The position of the mode doors determine where the air comes out at . The doors have vacuum controlled actuators , on the back of the mode switch vacuum lines are connected to it ! To check for vacuum at the switch you'll need to take HVAC control module out of the dash ! There is also a vacuum reservoir or tank under the dash near the HVAC assembly. You could look under the hood in the engine compartment an look for a disconnected vacuum hose from the engine intake manifold !
Step
Action
Yes
No

1

  1. Start the engine.
  2. Turn the blower motor fan ON and select an air outlet mode.
Does air flow out of the selected HVAC outlet ducts?
Go to Step 3 yes
Go to Step 2 no

2

Did the customer concern mention that the air discharges out the correct ducts at first, but then changes during higher engine RPM?
Go to Step 7 yes
Go to Step 3 no

3

With the engine running, cycle the HVAC controls through all the modes.
Does the air come out of the selected outlet ducts?
Go to Step 18 yes
Go to Step 4 no

4

With the engine running, take a vacuum reading at the manifold vacuum port that supplies vacuum to the HVAC control vacuum valve.
Is there engine vacuum?
Go to Step 6 yes
Go to Step 5 no

5

Repair the no vacuum condition.
Is the repair complete?
Go to Step 18 yes
--

6

Take a vacuum reading at the vacuum supply line at the HVAC control vacuum valve.
Is the vacuum reading the same as the engine vacuum?
Go to Step 11
Go to Step 8

7

  1. Disconnect the vacuum supply line from the HVAC control vacuum valve.
  2. With the vacuum gauge connected to the vacuum supply line, re-start the engine and turn the engine OFF.
Does the A/C system lose vacuum after turning OFF the engine?
Go to Step 8
Go to Step 11

8

Inspect for leaking or collapsed vacuum lines between the engine manifold vacuum port and the HVAC control vacuum valve.
Are the vacuum lines leaking?
Go to Step 9
Go to Step 10

9

Repair or replace the collapsed or leaking vacuum line.
Is the repair complete?
Go to Step 18
--

10

Replace the vacuum reservoir tank. Refer to Vacuum Tank Replacement .
Is the repair complete?
Go to Step 18
--

11

Using an external vacuum source, apply vacuum to the appropriate vacuum line at the HVAC control vacuum valve connector. Refer to HVAC Vacuum Schematics .
Does the actuator retract?
Go to Step 17
Go to Step 12

12

Inspect for leaking or collapsed vacuum lines between the actuator and the HVAC control vacuum valve connector.
Are the vacuum lines leaking?
Go to Step 9
Go to Step 13

13

  1. Disconnect the vacuum line from the actuator.
  2. Apply an external vacuum source to the actuator.
Did the actuator retract?
Go to Step 14
Go to Step 16

14

With the actuator disconnected, inspect the door for binding.
Does the door move freely?
Go to Step 16
Go to Step 15

15

Repair the binding door. Refer to the appropriate repair.
?€¢
Defroster Door Replacement


?€¢
Mode Door Replacement


?€¢
Recirculation Door Replacement

Is the repair complete?
Go to Step 18
--

16

Replace the vacuum actuator. Refer to the appropriate repair.
?€¢
Defroster Valve Actuator Replacement


?€¢
Mode Actuator Replacement


?€¢
Recirculation Actuator Replacement

Is the repair complete?
Go to Step 18
--

17

Replace the HVAC control vacuum valve. Refer to HVAC Control Vacuum Valve Replacement .
Is the repair complete?
Go to Step 18
--

18

Cycle the HVAC controls through all modes to verify proper operation.
Did you correct the condition?
System OK
--
Hope this helps an good luck !

May 08, 2015 | 2002 Chevrolet Impala

1 Answer

1998 windstar only blowing air out of defrost


Check under hood on passenger side. There are two hard plastic black vacuum lines that go to a ball (vacuum chamber). Trace them to the engine. Chances are one of them are broken. They are HVAC vent control vacuum lines. Usually when they break you're left with this symptom. Happy holidays.

Dec 25, 2013 | Cars & Trucks

1 Answer

2005 Silverado 2500HD 4WD - It appears that the pneumatic valve controlling the directional air flow from my heater/AC is getting stuck. When I switch the fan to front window defrost then back to...


The default configuration when all vacuum fails is to defrost vents. Most likely your vacuum supply to the switch is weak. Check the connection of the supply line to the intake manifold for damage. If no problem there, trace it to the switch on the control panel. If there is an accumulator, make sure it isn't leaking and is storing vacuum. If all this is good, look at any other vacuum lines connected to the intake manifold that may be leaking and possibly reducing the vacuum supply to the HVAC control line. Let me know if you have more questions.

Sep 28, 2010 | 2006 Chevrolet Silverado 2500HD 2WD

1 Answer

I have a 1999 Chevy Malibu and the AC turns from inside air output to outside output on it's own. You can push the inside air button and it will go back and then in a second or two it will go back to the...


Yes , the Refrigerant level is good , I would say the control panel is bad , or there is a problem with HVAC Air Delivery/Temperature Control Circuit Description
The vacuum actuators move the air valves in the HVAC system (except the temperature valve). Vacuum is applied to the actuators through the mode selector in the heater A/C control assembly. The mode selector consists of a rotary vacuum switch. The rotary vacuum switch supplies vacuum to the vacuum actuators according to the operating mode selected by the driver. A small servo motor moves the air temperature actuator. The small servo motor positions the door according to the voltage level from the temperature selector in the heater A/C control assembly. The temperature selector is a potentiometer positioned by the temperature control knob on the front of the heater A/C control assembly.
Air Temperature Actuator
When the ignition switch is in the RUN position, battery voltage is applied to the air temperature actuator. The actuator receives ground at all times through the following components:
• CKT 251
• Ground G204
The temperature selector is a potentiometer with a wiper arm. The wiper arm is electrically tied to the air temperature input through CKT 733.
When the temperature selector is moved between COLD and HOT, voltage to the control input varies between 1 and 12 volts. The temperature valve motor solid state circuitry performs the following tasks:
• Looks at the control input voltage
• Moves the motor to correspond to the control input voltage
The temperature valve moves for the following reasons:
• In order to allow the air to pass through the heater core
• In order to allow the air to pass around the heater core
This control achieves the desired passenger compartment temperature.

HVAC Air Delivery System Check
Step
Action
Yes
No
1
Start the engine.
Turn the blower motor fan ON and select an air outlet mode.
Does air flow out of the selected HVAC outlet ducts?
Go to Step 3
Go to Step 2
2
Did the customer concern mention that the air discharges out the correct ducts at first, but then changes during higher engine RPM?
Go to Step 7
Go to Step 3
3
With the engine running, cycle the HVAC controls through all the modes.
Does the air come out of the selected outlet ducts?
Go to Step 18
Go to Step 4
4
With the engine running, take a vacuum reading at the manifold vacuum port that supplies vacuum to the HVAC vacuum control assembly.
Is there engine vacuum?
Go to Step 6
Go to Step 5
5
Repair the no vacuum condition.
Is the repair complete?
Go to Step 18
--
6
Take a vacuum reading at the vacuum supply line at the HVAC vacuum control assembly.
Is the vacuum reading the same as the engine vacuum?
Go to Step 11
Go to Step 8
7
Disconnect the vacuum supply line from the HVAC vacuum control assembly.
With the vacuum gauge connected to the vacuum supply line, re-start the engine and turn the engine OFF.
Does the system lose vacuum after turning OFF the engine?
Go to Step 8
Go to Step 11
8
Inspect for leaking or collapsed vacuum lines between the engine manifold vacuum port and the HVAC vacuum control assembly.
Are the vacuum lines leaking?
Go to Step 9
Go to Step 10
9
Repair or replace the collapsed or leaking vacuum line.
Is the repair complete?
Go to Step 18
--
10
Replace the vacuum reservoir tank.
Is the repair complete?
Go to Step 18
--
11
Using an external vacuum source, apply vacuum to the appropriate vacuum line at the connector to the HVAC vacuum control assembly.
Does the actuator retract?
Go to Step 17
Go to Step 12
12
Inspect for leaking or collapsed vacuum lines between the actuator and the connector to the HVAC vacuum control assembly.
Are the vacuum lines leaking?
Go to Step 9
Go to Step 13
13
Disconnect the vacuum line from the actuator.
Apply an external vacuum source to the actuator.
Did the actuator retract?
Go to Step 14
Go to Step 16
14
With the actuator disconnected, inspect the door for binding.
Does the door move freely?
Go to Step 16
Go to Step 15
15
Repair the appropriate binding door.
Is the repair complete?
Go to Step 18
--
16
Replace the appropriate vacuum actuator.
Is the repair complete?
Go to Step 18
--
17
Replace the HVAC vacuum control assembly.
Is the repair complete?
Go to Step 18
--
18
Cycle the HVAC controls through all modes to verify proper operation.
Did you correct the condition?
System OK
--

Apr 05, 2017 | 1999 Chevrolet Malibu

1 Answer

I have an 89 chevy Celebrity Eurosport and the switch on my heater control will no longer switch the air from vent to defrost. There is no longer any resistance as I slide the mechanism. Anyone know how to...


There is a unit under the hood called a vacuum accumulator. Often times, more often than not, one of the two lines to this unit is cracked or broken. The accumulator is a black ball with two lines to it, one running from the intake manifold towards the rear, and the other running back through the firewall on the passenger side. Check both of these lines well. I'm certain that your problem lies within this area. If you don't find a problem here you've probably got to replace the climate control unit. Another good way to narrow this down is to run the vehicle for about 30 seconds and shut down the engine, then exercise the floor to defrost selections and listen carefully for a hissing and sweeping sound of the air flow control doors(flaps). Thank you, Dana

Sep 21, 2009 | Chevrolet Celebrity Cars & Trucks

3 Answers

I need a vacuum line schematic for a 2003 Chevy Astro Van. My AC only blows out of the defroster vents. I've replaced 2 lines so far but it has not fixed the problem yet.


Replace the complete heater control vacuum line over the motor with rubber vacuum tubing.
The heater vacuum line connects on the drivers side of the engine halfway back on the intake manifold.Run the new line to the heater vac connection at the passenger side at the right front in the engine compartment.
I change 2 a week....this should be where your problem is.

Sep 09, 2009 | 2003 Chevrolet Astro

1 Answer

Air only blows out on windshield & floor when


THERE IS A VACUUM LINE THAT GOES FROM THE LEFT FRONT OF THE ENGINE TO THE VACUUM CHECK VALVE NEAR THE ACCUMULATOR. IF THAT LINE IS BROKEN THE PROBLEM YOU HAVE IS NO HVAC MODE SWITCHING.

Jul 12, 2009 | 1998 Chevrolet Astro

1 Answer

98 Astro Van,when warm hesitating, stalling


WELL YOU CHANGED ALMOST EVERY THING EXCEPT IGNITION CONTROL MODULE........

Jun 27, 2009 | 1998 Chevrolet Astro

3 Answers

AIR FLOW STUCK IN DEFORST VENT WILL NOT SWITCH TO FLOOR OR AC VEN


I found a broken vacuum hose on top of the intake which runs the controls

May 07, 2009 | 2000 Chevrolet Astro

1 Answer

Hvac doors not working


Its probably the vaccum line. Check again. There is a small thin one that crosses over the top of the engine and fails/leakes/cracks in the area where it is hard to see. Repalcing the vaccum lines for $10 is the place to start. Then see what happens. While the engine cover is off, go ahead and change the PCV valve and give the engine a quick check for any other loose connections or issues.

Nov 13, 2008 | 1999 Chevrolet Astro

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