No heat in 91 Caprice Classic - Chevy Impala SS Forum
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post #1 of 14 (permalink) Old 12-12-2016, 04:29 AM Thread Starter
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No heat in 91 Caprice Classic

Hi fellas, winter is here and my HVAC was completely shot. I replaced the blower motor (major PITA) and blower motor resistor. I got air flow now, but no heat. Every setting seems to work except heat won't move air and defrost isn't hot. Is it the heater core or something else? Thanks in advance.
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post #2 of 14 (permalink) Old 12-12-2016, 06:51 AM
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Quote:
Originally Posted by GM4Life View Post
Hi fellas, winter is here and my HVAC was completely shot. I replaced the blower motor (major PITA) and blower motor resistor. I got air flow now, but no heat. Every setting seems to work except heat won't move air and defrost isn't hot. Is it the heater core or something else? Thanks in advance.
So it sounds like you have the heater working as it should (air flow) but just not getting hot? If you don't have much history on the car or it's been a while since it was flushed/maintained, I would consider a good flush of the system along with the heater Core.

See what the temps are of the 2 Heater Core hoses at the Firewall. If the outlet hose is colder then its most likely clogged HC. It could still be a blocked HC is both hoses are the same temp though. Could just be flowing through the upper half of the core and the bottom is so clogged that Hot Coolant is not heating up the entire HC. This can really limit your heat output.

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post #3 of 14 (permalink) Old 12-12-2016, 06:58 AM
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Is the blend door moving when you slide the cool/warm slide lever? It's cable actuated from the lever.
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post #4 of 14 (permalink) Old 12-12-2016, 06:05 PM
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The 91s have a vacuum operated diverter valve near the firewall in the engine compartment. If the valve is not working, vacuum is not ported, vacuum line is cracked/broken/detached, or the valve is clogged, it will cause a no heat situation. They are a weak point in the system.

1991 OCC 461 (.030 over 454) BBC, 3.23 posi, flash to pass, drop spindles & springs, Impala rims, Hydroboost, Recaros, MOMO/wood SW w/QR, custom wood shift knob, Pioneer DEH P77DH
1992 OCC now with 5.7 tbi, DEH P77DH
For a parts list, check https://www.impalassforum.com/vBulle...ion-parts.html
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post #5 of 14 (permalink) Old 12-13-2016, 01:29 AM Thread Starter
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Thanks for the replies guys. Is this something I can research and fix myself, or would I be better off taking it to a shop? I have a guy in town I trust but I like to try and take care of the more basic things myself as long as I have the right tools.
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post #6 of 14 (permalink) Old 12-13-2016, 07:15 AM
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You should be able to do it yourself. You do not need a lot of specialized tools. You should be able to borrow a vacuum tester from your local parts store for the shut off valve, and the rest is just making sure the hoses and core are clear. If it is the control panel, there is one part that can be bad for heat, and that is the actuating rod for the blend door (or its attachment ends).

1991 OCC 461 (.030 over 454) BBC, 3.23 posi, flash to pass, drop spindles & springs, Impala rims, Hydroboost, Recaros, MOMO/wood SW w/QR, custom wood shift knob, Pioneer DEH P77DH
1992 OCC now with 5.7 tbi, DEH P77DH
For a parts list, check https://www.impalassforum.com/vBulle...ion-parts.html
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post #7 of 14 (permalink) Old 12-13-2016, 07:31 AM
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Thanks for the replies guys. Is this something I can research and fix myself, or would I be better off taking it to a shop? I have a guy in town I trust but I like to try and take care of the more basic things myself as long as I have the right tools.
as was mentioned / suggested are the heater hoses both hot ????????????

if so then it is a door control problem in the box or a vacuum line . if the air ducts change from heat to vent then it may be a cable issue on the temp door.

if it does not change from heat to vent then check the small vacuum lines under the hood . also under the dash.

on a 1991 the rubber vac lines should be an issue on the complete engine compartment. check all for cracks and other damage.esp near the intake manifold .
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post #8 of 14 (permalink) Old 12-16-2016, 06:27 PM Thread Starter
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The hoses get warm and after driving the car for an extended period of time today, it seems like the defrost setting does get slightly warm once the car is driven awhile (while I was driving it was early morning between -1 and 5 degrees) but the heat is definitely not working how it is supposed to. The thing I don't understand is that why does every setting move air except heat? I called the mechanic that does my inspections and oil changes and he seems to think I need to flush the heater core, but won't know for sure until he takes a look. I live in an apartment and don't have access to outdoor water and it is so cold out I wouldn't really want to do it myself anyway. Do you guys think that could be the problem? Vent moves air but when I switch it over to heat it seems like it is blocked because there is no air flow. Every other option moves air on high, med, low, etc. Thanks again.

Last edited by GM4Life; 12-16-2016 at 06:31 PM.
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post #9 of 14 (permalink) Old 12-16-2016, 06:54 PM
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The system will not put out air from the AC vents when it is in heater mode, or defrost mode. The air will come out of the floor vents in heat. Defrost will come out of the defrost vent.

If the motor is not running at different speeds in the defrost and heater modes, you will have an electrical problem. It may be in the selector switch.


The vacuum line to the diverter valve in the engine compartment may not be transmitting vacuum to the valve. The control panel controls the vacuum to the valve.


The heat/AC door is moved by the temp lever directly and mechanically.

1991 OCC 461 (.030 over 454) BBC, 3.23 posi, flash to pass, drop spindles & springs, Impala rims, Hydroboost, Recaros, MOMO/wood SW w/QR, custom wood shift knob, Pioneer DEH P77DH
1992 OCC now with 5.7 tbi, DEH P77DH
For a parts list, check https://www.impalassforum.com/vBulle...ion-parts.html
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post #10 of 14 (permalink) Old 12-16-2016, 07:01 PM Thread Starter
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The system will not put out air from the AC vents when it is in heater mode, or defrost mode. The air will come out of the floor vents in heat. Defrost will come out of the defrost vent.

If the motor is not running at different speeds in the defrost and heater modes, you will have an electrical problem. It may be in the selector switch.


The vacuum line to the diverter valve in the engine compartment may not be transmitting vacuum to the valve. The control panel controls the vacuum to the valve.


The heat/AC door is moved by the temp lever directly and mechanically.
The motor does run at different speeds on all settings and in defrost mode air does come out of the defrost vent. I didn't realize the air came out of floor vents during heat mode, so it probably does move air because I can hear the motor running in heat mode.
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