Question about 1990 GMC Sierra

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Eratic control of heater temperature

It seems that I either have full heat or know heat. opposite/similiar problem on AC. Is there a vacuum leak? How do find it

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Try this, as there is a old TSB for this issue. Remove climate control head from dash, carefully dissasemble and clean electrical contacts with a little electrical contact cleaner, soft pencil eraser, Q-tips.Clean electrical plugs as well, carefully bend the conector tabs to be sure of good contact with control head. Apply a LIGHT coating of electrical grease to protect from further corrosion.Hope this helps!

Posted on Feb 01, 2009

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I replaced the heat blend actuator because I was not getting any heat. Now, after replacing, all I get is hot air and no cold. The A/C was working fine just before replacing.


Do you have Manual Climate Control System or Dual Automatic Temperature Control System ?
The temperature control switch:
  • is a potentiometer that outputs a variable voltage to the temperature blend door actuator to set the position of the temperature blend door.
  • initiates closing of the heater control valve. When set to full COOL, a lever on the temperature blend door pivot shaft depresses the pintle of the heater control valve vacuum switch. The heater control valve vacuum switch then applies vacuum to the heater control valve, closing off engine coolant flow to the heater core.
  • is serviced only with the climate control assembly.
You may have disturbed something when changing the actuator , the vacuum switch o vacuum hose .

Oct 21, 2015 | 2005 Ford Explorer XLT

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2000 grand prix, temperature won go from ac to heat, stuck on ac.


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2004 dodge intrepid 2.7l ......Heat works great while driving down the road but when stopped it blows cold?


The first thing you should do is make sure that you are not low in coolant as air can be introduced into the systemand cause circulation problems. If system is full, be sure that temperature gauge at normal operating temp is not fluctuating as there could be a thermostat problem. If that checks out okay, move onto check-in if the heater core may be plugged. To do this you must locate the 2 heater hoses that go into the firewall and feel the temperature of both of them with the heat turned on full. They sgould be around the same temp, if one is cold, that means the heater core is plugged up. Heater cores btw do not always need to be replaced if plugged, theu can be back flushed with pressurized water. Let me know if this helps good luck!

Feb 05, 2015 | Dodge Cars & Trucks

1 Answer

2000 envoy my heat was working but it made a loud whistling noise now it wont comeon at all hodo u tighten hose


Not an easy fix - sounds like either a heater/AC plenum control diaphragm started leaking, or a vacuum hose to one of them has popped off at the actuator or at the heater control, or the vacuum line developed a leak somewhere between an actuator and the heater control or the engine. You can try to pin down by checking airflow out of the defroster, ac and heater vents - if airflow is normal in each position, the problem is probably the heat/cool control actuator, the line from it to the heater control, or the heater control itself.

Nov 20, 2014 | 2000 GMC Envoy

1 Answer

'94 Ford Taurus-No Heat?


Good point. Solving it will probably take more time than money.
Thermostats and heater cores do not work one day and stop the next. If your engine warms up normally and doesn't overheat, the gauge reads normally, engine is at normal operating temperature after about 10-15 minutes ...all these point to a good thermostat. It is working right and should not be a problem.
To check the heater core, wait till engine is at normal operating temperature. Turn heat setting to high, then feel both heater hoses-both should be hot. If both are hot the core is circulating coolant and is not a problem. If only one is hot (which would be the inlet hose) the core is not circulating-could be an air block or the core is plugged up and will need replacing.
If heater core and thermostat are good, then it probably is the temperature blend door in the heater case. The door actuator is probably vacuum controlled. I don't know how difficult it is to troubleshoot on your Taurus, but check if vacuum controls are working right from the dash controls, check if the blend door is stuck, is broken, or if the vacuum control is working to open and close the blend door. When you want heat, the blend door should let blower air pass across the heater core.
From the engine you will have a single vacuum hose that goes through the firewall into the dash to the heater/AC controls. There, a pod like device can rout the vacuum signal to various doors on the heater case.
Good luck.

Jan 07, 2014 | Cars & Trucks

1 Answer

My heater does not blow in floor in a dodgeram 1500


the heater vacuum motor and lines needs to be checked.Also get the blend door checked.

NO HEAT ON FLOOR VENTS

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As per your problem mentioned. There are few solved help links to troubleshoot these problems. Go through the list and Click the link below:----

2000 Toyota Avalon: No heat on Passenger Side?

http://whatisbyme.blogspot.in/2012/05/2000-toyota-avalon-no-heat-on-passenger.html


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No heat on Oldsmobile Silhouette?


http://technoanswers.blogspot.in/2012/02/no-heat-on-oldsmobile-silhouette.html

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Heater blows cold?

http://schematicsdiagram.blogspot.in/2012/02/heater-blows-cold.html

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Heat blows cold on drivers side and hot on passenger side?

http://schematicsdiagram.blogspot.com/2011/12/heat-blows-cold-on-drivers-side-and-hot.html

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Hot air on the driver's side vents only?

http://repairhelpcenter.blogspot.com/2012/01/hot-air-on-drivers-side-vents-only.html

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Temperature gauge does not move and no heat when heater is ON?

http://technoanswers.blogspot.com/2012/01/temperature-gauge-does-not-move-and-no.html

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1992 Toyota Camry: A/C Control light Flashing and A/C not Blowing Cold?

http://technoanswers.blogspot.in/2012/04/1992-toyota-camry-ac-control-light.html

--------------

No heat, blower blows only cold?

http://technoanswers.blogspot.in/2012/02/no-heatblower-blows-only-cold.html

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Ford F150 Ac only blows through defrost vents?

http://technoanswers.blogspot.com/2012/01/forf-f150-ac-only-blows-through-defrost.html

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Dodge A/C come out of defrost vents only?

http://technoanswers.blogspot.com/2012/01/dodge-ac-come-out-of-defrost-vents-only.html

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Ac vacuum line on dodge cummins?

http://technoanswers.blogspot.com/2012/01/ac-vacuum-line-on-dodge-cummins.html

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Ford ranger AC blows cold through defrost vents instead on cabin vents?

http://technoanswers.blogspot.com/2012/01/ford-ranger-ac-blows-cold-through.html

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2005 Chrysler PT Cruiser: A/C Blows Warm?

http://whoisbyme.blogspot.in/2012/06/2005-chrysler-p8t-cruiser-ac-blows-warm.html

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2009 Mercury Grand Marquis: A/C blows Cold From Defrost Vent Only?

http://whoisbyme.blogspot.in/2012/06/2009-mercury-grand-marquis-ac-blows.html

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AC not blowing through Vents on 2007 Chevy Trailblazer?

http://schematicsdiagram.blogspot.in/2012/04/ac-not-blowing-through-vents-on-2007.html

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Passenger side temperature is warm air out of dash vents?

http://schematicsdiagram.blogspot.in/2012/04/passenger-side-temperature-is-warm-air.html

----------


These will help.

Thanks.

Nov 28, 2012 | Cars & Trucks

2 Answers

I have a mercury mountaineer 2003 V6. It has a problem of making sound repeated when I want to have heat turned on. No sound when the dashboard A.C/Heat stays at AC level, which is the zero? level. The...


When the engine is cold,check the coolant level.

Make sure it's on max.

===

A coolant system should be flush every two years.

===

If you did a coolant flush recently then air pocket can be the cause of the un-even heating problem.

The DIY method is to drive you car onto a ramp or a steep hill.

Iet the engine cool off and top off the coolant tank.

Set MAX heat + MAX fan

Let the engine ran for 20 minutes wih the cap off and the trap air will escape from the coolant reserve tank,

Check coolant level and top off coolant when the engine cools down.



A shop will charge $75+ for this but using an air operated excavate tool!

========

A car with over 90K miles may experience linkage problem to the heater control valve.

The heater control valve (near the firewall) may be stick over time.

Open the hood and move the heater to max and min. Back and forth.

Clean and lube the linkage with WD-40 to free the heater control valve.

If it's a vacuum type heater control valve then cash for leaky vac. hoses.


=======
Move the fan switch back and forth to re-new the electrical conductors.

Pass a vacuum over the control panel to prevent dust build up behind the console.

Sep 13, 2009 | 2003 Mercury Mountaineer

2 Answers

All i get from my heater is heat i cant turn the ac on, and when i turn off the heater it still blows hot air


Sounds like a stuck heater core valve. Find heater core valve. Under hood, find the two heater core hoses going into firewall. One of the hoses has a valve. Operate temperature control (full heat, then full cold) check that valve changes position. If not either replace valve or control system failure. Also, when temperature control in cold position, one hose should feel hot and the other cold. Temp fix: disable valve to close no heat or on heat.

Jul 10, 2009 | 1998 Dodge Ram 1500 4WD

1 Answer

2000 Silverado Z71. Heater stays in hot mode.


There are a couple of things you can check, or have checked. Under the dash, behind or around the ac duct work, there is vacuum operated actuator valves, which open and close different doors to direct heat or cool air,one of them might be stuck in the heat position.But the first thing to check, if the truck is equiped with it, is the heater control valve, it is under hood passenger side connected to one of the heater hoses going into firewall.Move the lever in opposit position, if you get cool air,thats the problem.If it's vacuum operated,check for leak,if no leak,replace valve.

Jan 22, 2009 | 2000 Chevrolet Silverado 1500

1 Answer

Heat in a festiva


You have a vacuum leak to the ac/heater mode control, or the control switch is bad or leaking vacuum, it can't be anthing else.

Nov 01, 2008 | 1993 Ford Festiva

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