Before I start, yes I have done the search and yes I have found much info. But I have a couple of questions I hope some one can answer. The Problem: Heat, no matter what setting the temp control is set to, even on full cool. Regardless of whether in auto or manual mode. Ok, I know the problem is that the valve that controls the coolant flow into the heaters core is staying open. So, it's either the AC ECU, motor that operates the valve, or the valve. ---- So I'm trying to diagnose the system. I do know that the compressor is in when I set the temp control to max cool (blue dot setting) as I can hear the clutch engaging/disengaging as I move the temp switch to and from the blue dot setting. I also know the temp control is basically working because when driving if I have it in automatic mode the fan speed will increase as I move the temp control to higher temperature. I can also feel the variation in air flow from the vents as I choose different vent setting. So basically, it seems that the hot water valve is staying open. So a couple of questions. 1) Does the car have to be up to temperature before the HVAC system will function correctly? That is, if the water temp is cold is the HVAC ECU smart enough to know not to blow cold air if the cabin tem is below the temp control setting? 2) I gather that the red/white and yellow/black wires supply power to the motor on the hot water valve. Is it ok to apply 12 across the terminals to test/check the motor and does any one know what polarity is correct to close the valve? 3) Does anyone know what the impedance of the motor should be? 4) I gather that the black, blue, and yellow wires are basically a potentiometer which is used to tell the ECU the position of the valve. Does any one know what the impedances should be when the valve is open and closed? Appreciate any help. And yes, my flapper is working correctly. So at press the stop button and recirculate button and prevent heating. FWIW, the AC was working fine during the summer. I took the car out yesterday and needed a little heat and after I turn it on I was unable for turn it off. I.E. after the hot water valve open I could not make it close, even setting the temp control to max cool.
The motor windings resistance is 390 Ohm, the potentiometer is 5.6 K. The two end pins are for the motor, the middle 3 are the potentiometer. In the closed position, the resistance between two of the three pot pins should be about 1 K (see pic). The picture shows the closed position; note the position of the rectangular block being near its stop (it doesn't have to hit the stop to close the valve, just to come to about 3-4 mm from it). You can connect 12V to the two end pins in one orientation and see whether the rectangular block is moving and which way; swap the + and - to change the direction of rotation. Looking from top, the block will rotate clockwise to close the valve. Image Unavailable, Please Login
John my guess is it is just sticky. For what its worth i use the heat about once a month even if its just for 5 min when watming up the car because mine did this once. The other benifit i found is that when my car was in the desert and only on AC the front would leak a small amount of coolant. By doing this it also stopped the leak. Sorry its not a solution but like anything that gets old it seems to be lack of use that causes problems. At least for me. Good luck and please keep us all up to date.
Thanks. I verified that the pot is 5.6k ohms between pins 2 and 4. My valve was open, seemed against the stop and the impedance where you measured 1k was about 3k. Motor impedance was about 47 ohms. I was able to close the valve by applying 12v to the motor. When closed the pot impedance where you read 1k was 7 ohms. The pot reading, as expected, will be sensitive to the actual position of the valve. I would question you motor impedance being 390 ohm. Are you sure it wasn't 39 ohm? 390 seems high for an automotive application. As an example, the flap motor has an impedance of 27 ohms. I'll have to wait until later to check to see if it was just stuck of or if there is a problem else where. Tanks again for the assistance. Nice concise answer to my questions.
Of course it cannot be 390 Ohm. I found out that it was because I have been keeping it for a couple of years without turning the motor so the brushes developed additional resistance. I ran it a few times open-closed and then measured the resistance of 60 Ohm. If I run it another 10 times it will probably come down further so your measured 47 Ohm seems good.
+12 V applied to the yellow/black, red/white ground for close. +12 V to Red/White, yellow/black ground for open.
Anyone have any experience with these guys? They seem to repair a wide variety of automotive electronics. Ferrari 355 360 430 Climate Control Programmer Computer
Bumping this thread. I have a malfunctioning HVAC ECU and was also curious if anyone has used ASI to repair their F355 HVAC ECU. Johnk posted a link to their web site above. Thanks.
The link is for Automotive Scientific Inc. If you then put that name into Google, you'll find some scary reviews. Of course you never know the truth behind complaints, but there are several, so be careful.
Regarding the uncooperative heater valve, can you separate the motor from the valve to test each component individually?
The valve/motor works fine. I tested it. It's not getting a signal from the ECU. I don't pay much attention to bad internet reviews. It's generally dissatisfied people who post reviews. Automotive Scientific Inc has 99.9% positive feedback from 1465 clients over the last 12 months on Ebay. Seems reasonable. http://feedback.ebay.com/ws/eBayISAPI.dll?ViewFeedback2&userid=ate1234&iid=131193026125&de=off&items=25&which=positive&interval=365&_trkparms=positive_365
Hey guys. I suspect the issue is your heater ecu. It's known to fail and cause all sorts of issues. I sent my ecu to these guys and they verified it was faulty and repaired it. Put it in the car and happy days the heat works a treat. Hope this helps. Cheers Andy.
Great to know that there folks out there that can fix this stuff for a reasonable price. Are you sending yours there John?
Thanks all. I had googled them before bumping the thread again, but you have to take all of it with a grain of salt. I trust the personal experiences of the folks on FChat more than the google 'truth' machine.
