cold heater - LotusTalk - The Lotus Cars Community
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post #1 of 7 (permalink) Old 05-18-2019, 03:43 PM Thread Starter
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cold heater

After replacing a defective thermostat that wasn't closing, I was hoping the heater would blow warn air. At 80 degree celsius plus it's still cold. Any suggestions on what to do before diving blindly into the dash would be very much appreciated. Thank you, Jim
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post #2 of 7 (permalink) Old 05-18-2019, 04:01 PM
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What year?

Do you have the Service Notes manual?

I am going to refer to some pages if its the right year. looks like an 89 or 88?

94 Esprit S4 - Silver
Previous - lots of hot rod Air Cooled 911s
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post #3 of 7 (permalink) Old 05-18-2019, 04:45 PM
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FIRST: You know that only cold air comes out of the face-level vents, right? Turn the heater controls to INTERIOR to get warm air. Feel the defrost vent to verify.



If that is not the case, there are two common causes on 4 cylinder cars:


1. Broken 'elbows' on the heater air-mix vacuum controls. This results in a vacuum leak and inoperative doors inside the dash. Peek up 'n under the glove box or remove the head unit to access and inspect. Also check the vacuum connection over the RH fuel tank (that goes forward on the RH side of the car).

2. Clogged heater core. If the car has been run for years with the heat temp control 'off' the coolant was not circulating. You can disconnect the small hoses under the front of the car and flush the core with a solution of CLR (but you need to rinse it well).

There are Topics here and on TheLotusForums that detail the remedies. It is Good Practice to run with the heat control at the 5 o'clock position so that there is always some flow through the heater matrix.
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'88 Esprit
Succasunna, NJ USA


"Not all angels have wings." - Turbo R
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post #4 of 7 (permalink) Old 05-18-2019, 06:18 PM
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Only one more thing I would suggest would be to check the heater valve. On my S4s mine was stuck and wouldn't open. Got a new one and it works fine now. BTW access to the valve was thru the bonnet firewall near the fuse box.
I had to cut a larger hole to get to it. Good luck.
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post #5 of 7 (permalink) Old 05-19-2019, 03:25 PM Thread Starter
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Thanks for all the info. No i did not know that the face level vents only blow cold air until now. After reading my owners manual I learned how to turn them off and how the heater/AC knobs work. So, after warming up the car and playing with the knobs, here's what I got. Warm air does flow but ever so slowly. When turning the knob from floor to defrost the air flow changes but very little air comes out. Unlike the face level vents that blow like crazy. The other thing I noticed is that the big flap that's under the bonnet stays closed at all times no mater what I do with the controls. I have had the radio out and everything seemed to be connected and working at that location. Thanks again for any advice, Jim 93my
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post #6 of 7 (permalink) Old 05-19-2019, 04:55 PM
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The picture below shows how the vacuum lines are situated. All the little vacuum system 'elbows' are shown. This is in the elusive Section PD of the service manual...do you have that section? GRIN


Since your vacuum-actuated air intake flap (under the bonnet) doesn't open, I suspect that you have a vacuum issue. Did you pull the carpeted cover off the RH quarter window area and check the vacuum line connections?

Also... since you have a '93 we need to ask, does your car have power steering (indicating it is a 93.5)? If it doesn't, it has a vacuum pump at the LF side of the engine. The rubber fittings right near the crankshaft can crack when doing other work, reducing the vacuum available. (If you want to test with a gauge, you are looking for 18hg minimum up above the RH gas tank.)

If you DO have power steering,, your HVAC vacuum is provided by an electric pump in the compartment on the rear engine wall. An S4s owner I visited today found that his EBPV line was leaking (yes he had wired the valve open) so his pump would run 'forever'. Putting a cap on the control solenoid source (right-most on the engine side) allowed the electric pump to maintain vacuum by only running every few minutes.


++++++++++++++

One other thing to look for when you inspect the controls behind the radio: The actuator shafts that switch the vacuum on and off are supposed to have little plastic caps on their ends, that ride on the control cams. If those have fallen off, the modes won't work.


Post back when you get a chance to investigate....
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Atwell Haines
'88 Esprit
Succasunna, NJ USA


"Not all angels have wings." - Turbo R
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post #7 of 7 (permalink) Old 05-27-2019, 05:21 AM Thread Starter
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Thank you Carbuff you nailed it. After spending an hour researching and probing into the RT rear of the vehicle and under the dash, I pulled the stereo. See pic of disconnected vacuum line. Thanks again,Jim
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