Heater core replaced, now AC line is freezing
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HT4100 4.1, 4.5, 4.9 Discussion, Heater core replaced, now AC line is freezing in Cadillac Engine Technical Discussion; Hi guys....First time posting here.....I belong to other forums, so here it goes. I own a 93 Sedan DeVille with ...
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    screwu2man is offline Cadillac Owners Member
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    Heater core replaced, now AC line is freezing

    Hi guys....First time posting here.....I belong to other forums, so here it goes. I own a 93 Sedan DeVille with the 4.9. i had the water pump replaced and had heat again. then lost it. I replaced the heater core and when ya turn the heat on it blows cold air and the ac lines freeze up. Now when i disconnected the AC compressor, it blows Nice heat, but now no A/C. is there something i am missing? A sensor? I dont know i am just about to give up. is there a test i can do? ANy help would be great. Thanks

    93 Sedan DeVille 4.9

    85 Fiero GT

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    cadfan is offline Cadillac Owners Member
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    Re: Heater core replaced, now AC line is freezing

    Quote Originally Posted by screwu2man
    Hi guys....First time posting here.....I belong to other forums, so here it goes. I own a 93 Sedan DeVille with the 4.9. i had the water pump replaced and had heat again. then lost it. I replaced the heater core and when ya turn the heat on it blows cold air and the ac lines freeze up. Now when i disconnected the AC compressor, it blows Nice heat, but now no A/C. is there something i am missing? A sensor? I dont know i am just about to give up. is there a test i can do? ANy help would be great. Thanks

    93 Sedan DeVille 4.9

    85 Fiero GT
    Sounds like a a/c programmed problem. It might be the programmer temp blend door is not operating.

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    Katshot's Avatar
    Katshot is offline Cadillac Owners Master
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    Re: Heater core replaced, now AC line is freezing

    Anytime you select an "AUTO" setting, the A/C compressor can come on depending on ambient temp, that's normal. The A/C lines "freezing" is also normal especially if it is a humid day out. The heater in these cars works by re-heating the cooled air that is produced via the A/C evaporator. A "properly" operating heating system will easily overwhelm the cool air and turn it hot. In your case, the heater is probably NOT producing sufficient heat to overwhelm the cool air. Are you sure you have the hose hooked-up properly? Did you ever check for a head gasket leak? Did you check the blend door calibration? These are all things that you might consider.

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    screwu2man is offline Cadillac Owners Member
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    Re: Heater core replaced, now AC line is freezing

    Quote Originally Posted by Katshot
    Anytime you select an "AUTO" setting, the A/C compressor can come on depending on ambient temp, that's normal. The A/C lines "freezing" is also normal especially if it is a humid day out. The heater in these cars works by re-heating the cooled air that is produced via the A/C evaporator. A "properly" operating heating system will easily overwhelm the cool air and turn it hot. In your case, the heater is probably NOT producing sufficient heat to overwhelm the cool air. Are you sure you have the hose hooked-up properly? Did you ever check for a head gasket leak? Did you check the blend door calibration? These are all things that you might consider.
    How would i go about looking for a head gasket leak? Not much of a motor guy here. As for all the other lines they seem to be working fine. but goin to screw with it today and look to see if there is a vacume leak, or something is not hooked up right, and check the codes. Thanks for the help so far.

    Keith

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    Katshot's Avatar
    Katshot is offline Cadillac Owners Master
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    Re: Heater core replaced, now AC line is freezing

    To be honest Keith, a regular mechanic could tell you in a heart-beat if it's bad but without a couple simple tools and some experience, you would probably NOT check it right and probably come up with the wrong diagnosis. You're looking for a slight leak in the head gasket that would be dumping gas (air and combustion gases) into the cooling system. This gas can accumulate in the heater core and cause a lack of heat.

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