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I've got a '93 Seville with the 4.9L. I'm having some problems with the HVAC system. There is almost no airflow through the defrost and main ducts. The blower motor sounds as though it is changing speed correctly with the controls, and when set on "hi" the blower is definetely working hard. I first suspected a vacuum loss to the programmer, but the vacuum supply is good. The programmer has a small electric motor that appears to operate the blend door...it is working correctly. I took the cover off the programmer, and all 4 of the electric-vacuum solenoids are operating. I can open the ducts individually with a small hand-held vacuum pump...and each of the servos holds the vacuum. The hoses going into and out of the heater core get hot. The most air comes through the main vents when the interior ambient temp is set at 60 F. According to my owners manual, the 60 F setting closes the outdoor airdoor and recirculates interior air. It just seems like the blower motor is beating the air. Is there another blend door, or possible blockage that I'm missing? One of the other thoughts that is sticking in the back of my head is related to the interior ambient temperature sensor. I suppose it could be reading a higher than actual temperature, therein the programmer would see no need to heat.

One other piece of info...the ac system is currently low on its refrigerant charge. I don't know how/if this effects the duct operation for the heating system. I was holding off on the R-134a retrofit until the spring. I've heard that you have to "adjust" the high and low temperature line sensors with resistors to adjust for the 10% to 15% difference between the R-12 and R-134a refrigerants...so the programmer "sees" the correct low and high temperature in the refrigerant line. I hope the answer pops out to someone. Low temp tonight is around 25 F.
 

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lonewolf79 said:
I've got a '93 Seville with the 4.9L. I'm having some problems with the HVAC system. There is almost no airflow through the defrost and main ducts. The blower motor sounds as though it is changing speed correctly with the controls, and when set on "hi" the blower is definetely working hard. I first suspected a vacuum loss to the programmer, but the vacuum supply is good. The programmer has a small electric motor that appears to operate the blend door...it is working correctly. I took the cover off the programmer, and all 4 of the electric-vacuum solenoids are operating. I can open the ducts individually with a small hand-held vacuum pump...and each of the servos holds the vacuum. The hoses going into and out of the heater core get hot. The most air comes through the main vents when the interior ambient temp is set at 60 F. According to my owners manual, the 60 F setting closes the outdoor airdoor and recirculates interior air. It just seems like the blower motor is beating the air. Is there another blend door, or possible blockage that I'm missing? One of the other thoughts that is sticking in the back of my head is related to the interior ambient temperature sensor. I suppose it could be reading a higher than actual temperature, therein the programmer would see no need to heat.

One other piece of info...the ac system is currently low on its refrigerant charge. I don't know how/if this effects the duct operation for the heating system. I was holding off on the R-134a retrofit until the spring. I've heard that you have to "adjust" the high and low temperature line sensors with resistors to adjust for the 10% to 15% difference between the R-12 and R-134a refrigerants...so the programmer "sees" the correct low and high temperature in the refrigerant line. I hope the answer pops out to someone. Low temp tonight is around 25 F.
I found the problem, for anybody that might have been running into a similar problem. The primary fault was a loss of most of the air flow. All servos and the blend door were working properly. I pulled the ATC Power Module for the blower motor. This gave me a good look at the evaporator core. It was clogged. The mesh "filter" that was used from the factory had dissolved into a...well a mess. It clogged the evaporator core, therein greatly restricting the airflow. I cleaned the goo off of the core, and now everything is great.
 
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