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94 Chevy Pickup no heat

kourso on Tue October 13, 2015 12:35 AM User is offline

Year: 1994
Make: Chevrolet
Model: Pickup
Engine Size: 5.7
Refrigerant Type: 134a
Country of Origin: United States

My AC comp. is shot but this truck's heater doesn't work well.
You only feel very slight air warmness.
I have confirmed that the driver side AC servo motor seems to function.
Is there another servo motor on the passenger side of the AC heater box ?
I am lost in what can be keeping the heater from working well ?
I replaced the AC evap. core years ago and that is when the heater went out.
Yet you can move the climate cont. control from cold to hot and tell the air warms very slightly.
I must get this heater working for this winter.
Please let me know what I can do to resolve this.

Note:
Also the heater core in & out hoses both get very hot as they should.
Seems like just a very little amount of air is crossing the hot heater core ?
Would that be because of a problem with the pass. side door blend servo motor ?
Is there one r two AC heater box servo motors on this model pickup ?
Thank you

GM Tech on Tue October 13, 2015 7:43 AM User is offline

You have only one temperature door- remove actuator and see if door moves freely- temp door actuator is bottom center as I recall- Have seen actuators fail with your same failure mode..

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The number one A/C diagnostic tool there is- is to know how much refrigerant is in the system- this can only be done by recovering and weighing the refrigerant!!
Just a thought.... 65% of A/C failures in my 3200 car diagnostic database (GM vehicles) are due to loss of refrigerant due to a leak......

kourso on Tue October 13, 2015 2:39 PM User is offline

GM Tech
I have seen the servo motor moving positions as I go from cold to hot in the climate cont. panel. And the air temp. increased very slightly. I could feel a little heat but not nearly as it should be. I had thought the engine thermostat was the cause but the heater hoses in/out the heater core are very hot to touch. I will take the servo off and see if the door moves easily.
So you think it has failed and just doesn't travel/move far enough ? As you said it is very common to this year model. Thank you

HECAT on Tue October 13, 2015 3:08 PM User is offline

Not to discount the blend door air flow issue. Heater core clogging with buildups is also very common. The hot lines in and out do not confirm, as the hot water may only be flowing thru a very small portion of the core.

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HECAT: www.hecatinc.com You support the Forum when you consider www.ackits.com for your a/c parts.

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GM Tech on Tue October 13, 2015 7:49 PM User is offline

Have you seen this- yours is a 94 but some issues may apply:

http://www.heatertreater.net/magento/chevrolet/silverado/99-12/chevrolet-silverado-1500-series-99-12.html

-------------------------
The number one A/C diagnostic tool there is- is to know how much refrigerant is in the system- this can only be done by recovering and weighing the refrigerant!!
Just a thought.... 65% of A/C failures in my 3200 car diagnostic database (GM vehicles) are due to loss of refrigerant due to a leak......

Edited: Tue October 13, 2015 at 7:50 PM by GM Tech

kourso on Tue October 13, 2015 11:01 PM User is offline

I looked at the servo motors, which there are 3 of them, which all look the same. But they do have different functions.
All are working. The middle one which is straight behind the radio in the center of the truck, regulates the air temp.
It moved as I changed from cold to hot. I didn't think it moved enough so I removed it and tried to move the blend door further. It didn't move any further but it moved fairly easy. Could the blend door not be sealing as it should ?
The only thing that I found was a plastic bag that was sucked toon the interior air circ. unlet right below the fan motor.
I had noticed when you turn on the max. AC/fan position. The frt. vent air flow would decrease? Would that have greatly affected the air temp. by restricting the interior air flow across the heater core ???
I just know this truck doesn't have a good working heater in the winter !!!
Please let me know what else can be done to get some hot air going?
Also the heater core was replaced at the same time as the AC evap. Core. and it hasn't worked much at all since.
Thank you

kourso on Tue October 13, 2015 11:07 PM User is offline

I was very surprised to see that trucK model had 3 HVAC servo motors. One on the lower left side, the 2nd servo was exactly in the center of the truck, High on the HVAC plastic case right behind the radio. The third servo is located on the passenger side, low behind the HVAC fan blower.

GM Tech on Wed October 14, 2015 9:05 AM User is offline

As a last resort you can try reversing the heater hoses on the fire wall- I have had this work once in my life-- my have different size hoses--

-------------------------
The number one A/C diagnostic tool there is- is to know how much refrigerant is in the system- this can only be done by recovering and weighing the refrigerant!!
Just a thought.... 65% of A/C failures in my 3200 car diagnostic database (GM vehicles) are due to loss of refrigerant due to a leak......

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