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Discussion Starter #1
Should a '92 Daytona 2.5L T1 have a heater control valve under the hood, I can't find one. Also can't find one on my '91 both T1 and N.A.. Parts catalog shows both ways in picture form, but there is no listing for the number for the valve. So is it supposed to be just a straight run from the water pump to the heater core and then back to the thermostat housing?
 

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Check the frame under the battery on the driver's side. Or follow the 5/8" hose from the water pump to the valve at the frame near the bottom of the radiator, on the left side. most of the newer water pumps have a dedicated nipple for the heater. One may also follow the hoses at the fire wall. One hose taps hot water from a fitting under the head just before the thermostat housing, just below the temp. sensor. This hose brings the hot coolant into the heater core. The coolant is drawn back to the water pump via the heater control valve. A small vacuum line runs from the fire wall, past the brake booster and down to the valve, too. It might be easier to spot it from under the car! I hope this helps. Nat Asp should locate the valve closer to the fire wall, right next to the brake booster.
Mark Leon
 

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Discussion Starter #4
I have 2 '91 EFI that looks like Fig 11, not valve. My '91 T1 and '92 T1 look like F 11 except that the one line doesn't go to the intake manifold, it just goes straight to the thermostat housing. Heater controls work fine in all the '91, but doors don't move in the '92. Figured that maybe previous owner swapped hoses and removed the valve, he did some other funky stuff under the hood, thought maybe it was related.
 

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The only thing the heater control valve does is stop coolant flow into the heater core when the A/C is set to Recirculate (max A/C).

Mode doors not moving would be (assuming you are stuck on defrost which is default) is a vacuum problem into the control unit.

If you are stuck on panel or floor then the issue could be a stuck vacuum motor or mode door.
 

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Discussion Starter #6
Pretty sure I checked for vacuum when I first looked into the problem. It's stuck on defrost. I got a replacement heater control panel, I'll have to dig that up and try swapping it. This is all preliminary work leading to (finally) getting the A/C conversion done.
 

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Defrost is default for safety reasons, no vacuum to the control unit = defrost.

Remove the control unit and verify engine vacuum is present at the vacuum in port.

You could have a broken/disconnected/collapsed line underhood. faulty or incorrectly installed check valve or broken/disconnected/collapsed vacuum line under dash.

HVAC 91-92.jpg
 

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A/C conversion ... this being a heat only car ??

if so fixing what you have now with heat only is pretty much a waste of time unless it's still gonna be some time before you get to do the conversion

at which point your heat only box and vac harness become a few spare parts

yes it's nice to know everything works before starting a conversion of most things but in this case , not so much if you're doing the conversion soon

maybe save a dive under the dash and start the conversion as the repair , by replacement ?

However .. checking you have a good vacuum source BEFORE the controls is a good place to start

the check valve in the vacuum source line coming into the car will either be right at the brake booster or inside under the dash right after the vac line comes in through the firewall
 

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Those heater control valves are junk!
I’ve run w/o them and see virtually no difference with or without them.
And just a side note, just about every one I have removed, leaky or not, are inoperative when removed.
So, replace if you wish, but in my opinion, it’s a waste of time and money, unless your looking to restore to original.


Sent from my iPhone using Tapatalk
 
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