Diesel Posted January 27, 2005 Report Share Posted January 27, 2005 I have been searching the archives for my HVAC fan problem with my 1994 DeVille, but have not quite found it. I was hoping someone might be able to help me out. This winter, the blower fan has not been working most of the time when I need heat. Even when the engine warms up and the fan is on high (in override mode), the fan doesn't work. However, if it is 60 degrees F or so, the fan works great. I am in Alabama, so we have had plenty of warm days this winter, and some days I run the A/C. The fan has never failed to operate when the interior is 65 F or above. Also, even on cold days, when the sun has heated up the interior, the fan and the heat works fine. The fan failure seems to be directly related to a cold interior temperature. I would suspect the inside temperature sensor is somehow cancelling the signal to the fan altogether when it is cold inside so that it doesn't even work on high. Has anyone ever had this problem? Where is the inside temp sensor located and is it easy to get to? Or am I off track with my attempt to diagnose? Thanks in advance. Link to comment Share on other sites More sharing options...
Scotty Posted January 27, 2005 Report Share Posted January 27, 2005 Move to Miami! Just kidding When I get a chance I will look my manual over, I don't think I have heard of this happening before. When I initially read your post I was like >> <<. Then, all of a sudden the light went on in my noggin! My guess is that this has something to do with the HVAC related coolant sensor signal in conjunction with the outside temperture. If I recall, in cold weather, below a certain temperature, the fan is locked out from running till the coolant temp reaches approximately 125 degrees. This is done so that when it is cold out and your car is cold, you don't get blasted with cold air while the coolant warms up to provide heat, smart idea if you ask me. Its possible that in cold weather, the sensor that is suppose to tell 'the system' that your engine/coolant has reached 125 degress is laying down on the job....and your fan is not commanded on. Let me do some bathroom reading on this and I will come back to this thread... Mike Link to comment Share on other sites More sharing options...
Scotty Posted January 27, 2005 Report Share Posted January 27, 2005 Thanks Guru But if the coolant temp threshold for the fan to kick on in cold weather is 125 degrees, even with a stuck thermostat the coolant temp would rise above that don't you think? I am thinking that the coolant sensor failed and a code has set, but wouldnt a failed coolant sensor cause drivability problems also? Lets see if there are any codes. Link to comment Share on other sites More sharing options...
adallak Posted January 27, 2005 Report Share Posted January 27, 2005 Diesel, What is the temp. setting? does it start when it is set at 90 degrees? The saddest thing in life is wasted talent Link to comment Share on other sites More sharing options...
Diesel Posted January 27, 2005 Author Report Share Posted January 27, 2005 Thanks for the brainstorming guys. When it is cold, and the fan is not running, I have tried all temp. settings between 60 and 90 degrees. It will not run at any temperature. I have tried it on auto, econ, and defrost - nothing. However, it was nice and sunny today around 70 degrees and I ran errands for about 2 hours with the fan running fine. I can say that when it is cold the air coming from the duct is sufficiently warm, because when I am going down the highway I can reach down with my hand and feel the warm air being forced through slightly from the air currents at 70mph, but the fan won't run. I recently had a small leak in the heater hose where it connects to the intake and have repaired it. When it was leaking, it was dripping down on what looked like a sensor. Is this the coolant sensor ya'll are referring to? I checked the codes right before I made the post. I had my usual (IO39) Service Ride Control thing, and a couple of memory codes because I recently disconnected the battery - but nothing relevant to the heater. I will run through the diagnostics tomorrow and see what the operating temperature is. Thanks again. Link to comment Share on other sites More sharing options...
Diesel Posted January 27, 2005 Author Report Share Posted January 27, 2005 The thermostat may be worth looking into because when I left work last night, it was only slightly cool in the high 40's or low 50's Farenheit (ambient temp.). The fan ran as soon as I started the car and warmed the interior up well. I then got on the interstate and did 70mph for about 5 miles and when I exited - no fan for the rest of the trip. Maybe the airflow of cool temps is keeping the coolant temp. low? But shouldn't the fan still work on high? Or can the sensor be malfunctioning in that respect as well (all or nothing)? I will check my temps with the diagnostics next trip I take, hopefully one cold and one warm to compare. Link to comment Share on other sites More sharing options...
Diesel Posted January 27, 2005 Author Report Share Posted January 27, 2005 I checked the engine temp. in the diagnostics this morning. Ambient temp. was 40 F. Engine temp started out 22 C and warmed up to 99 C. Blower fan would not come on. Bbobynski, I will go ahead and keep this thread over here unless I get some other feedback on Cadillacforums. Thanks. Link to comment Share on other sites More sharing options...
adallak Posted January 27, 2005 Report Share Posted January 27, 2005 Diesel, have you ever got the real coolant temperature reading on your DIC? It may happen ( I really do not know how and why) the PCM gets wrong input from the sensor. The coolant temp. should be some 194-200 at highway speeds in the summer and some 10-1 degrees lower in the winter time. If you get signifucantly lower numbers - that would be the problem. You can set your DIC so that you would be able to monitor the tem. in real time. The saddest thing in life is wasted talent Link to comment Share on other sites More sharing options...
Scotty Posted January 27, 2005 Report Share Posted January 27, 2005 Here is the blower diagnostic chart for NO BLOWER OPERATION/IMPROPER BLOWER SPEED from my 96 manual, I dont know if its the same as your 95, but I thought it could shed some light on this. I know you dont have a tech 1, but I believe you can override the commanded blower in ACM, I dont have the Diagnostic Flow Chart for any system other than PZM, does anyone know where detailed Diagnostic Flow Charts are for all the systems? I had a separate handbook for my 91, the 96 manual doesnt seem to have the detail... Link to comment Share on other sites More sharing options...
Scotty Posted January 27, 2005 Report Share Posted January 27, 2005 Here is more information from the manual regarding no blower or improper blower speed. Link to comment Share on other sites More sharing options...
Diesel Posted January 28, 2005 Author Report Share Posted January 28, 2005 bbobynski/adallak, Yes, I am sure I was checking PD04 - Engine coolant temp. I watched it climb up to 99 C while it was idling this morning. The wife drove it about 40 miles and the blower never came on. The car sat in the sun for about 2 hours while she was parked (nice and toasty inside), then when she got in the car to leave, the blower worked 40 miles back home. Scotty, Thanks for the diagnostic chart. I am going to study up on that and see what I can find. Thanks to all of ya'll. Iv'e never had such attentive help on a forum before. Looks like there's a good chance we'll figure this thing out. Link to comment Share on other sites More sharing options...
adallak Posted January 28, 2005 Report Share Posted January 28, 2005 Real mystery! Only thing you can do before the fix is found is leaving the air mix door wide open by setting at 90 degrees. This way you will get maximum natural air flow through the heater core. I personally do just that and use the blower occasionally. At highway speeds and some 2000-3000 rpm you will get a lot of heat for Alabama. The saddest thing in life is wasted talent Link to comment Share on other sites More sharing options...
adallak Posted January 28, 2005 Report Share Posted January 28, 2005 Looks like it has something to do rather with interior temperature than coolant's. Did you try to tap a little bit the PCM which is under the glove box (easy to remove, juat a couple of screw)? Or maybe some relays in the cabin? The saddest thing in life is wasted talent Link to comment Share on other sites More sharing options...
navion Posted January 28, 2005 Report Share Posted January 28, 2005 Diesel, I had a similar but not identical problem with my 94 SLS. The fan wouldn't run at all most of the time, but occasionally it would work fine until the next time that the engine was shut down. After trying several things, I found that the connector right at the fan had high resistance. It had slightly deformed the plastic thet the three wire plug was made from. When I pulled it from the HVAC motor and looked in at the connections, one of them had obviously been hot. I took out my trusty Leatherman and VERY GENTLY squeezed the offending connector so it would grip it's mate on the motor. VOILA It worked! It has been several months and it hasn't acted up since. It may not be what is wrong with yours, but it is worth a look. I had to look closely at mine before I noticed what was wrong. If I hadn't noticed the slight signs of heat & high resistance, I probably would have replaced the motor. In fact, I was just giving it "One More Look " before I ordered that da** expensive motor. Good Luck, Let us know what you find. Britt Britt Link to comment Share on other sites More sharing options...
Silver Posted February 7, 2005 Report Share Posted February 7, 2005 Can anyone tell me where the in-car temperature sensor is in a 1995 Deville and if it is hard to replace? I am still trying to isolate the problem with this blower fan. Thanks. Link to comment Share on other sites More sharing options...
Ranger Posted February 7, 2005 Report Share Posted February 7, 2005 Can anyone tell me where the in-car temperature sensor is in a 1995 Deville and if it is hard to replace? I am still trying to isolate the problem with this blower fan. Thanks. I have never had to replace one but if you find the little square grill in the dash (approx. 1" sq.) it will lead to the sensor. The grill is the asperator intake and the sensor is in that intake line. Link to comment Share on other sites More sharing options...
Silver Posted May 26, 2005 Report Share Posted May 26, 2005 I just thought I would follow up on the thread I started. The problem turned out to be the blower fan. The fan, or some component of it, was sensitive to cold weather. It works great in the summer. I replaced it with a new one. As an experiment, I put the old one in a refrigerator for a day and then put 12 v to the "c" terminal and grounded "a" & "b". The fan would not work, it would just turn back and forth about half an inch. I put it in the sun for an hour and it came on full speed. There is lots of good info on this forum - Thanks everyone. Link to comment Share on other sites More sharing options...
Northstar Posted May 26, 2005 Report Share Posted May 26, 2005 Did you ever put a test light on the positive going to the fan when it would not come on? Link to comment Share on other sites More sharing options...
Diesel Posted May 27, 2005 Author Report Share Posted May 27, 2005 I just realized my previous posting was under a different name (Silver) - oops. Yes, I had tested for 12 v on the positive lead and it always had juice there. I had read on the forum of the above method of wiring the fan directly to a battery in order to isolate the fan as the problem. When the fan was working, I could "hotwire" it (ignition off of course) and it would work. When the fan did not work I hotwired it and it did not work. I just did the refrigerator thing after I had it out in order to prove it was temperature related. Hope this helps someone. Link to comment Share on other sites More sharing options...
New Caddy Owner Posted November 26, 2006 Report Share Posted November 26, 2006 I just realized my previous posting was under a different name (Silver) - oops. Yes, I had tested for 12 v on the positive lead and it always had juice there. I had read on the forum of the above method of wiring the fan directly to a battery in order to isolate the fan as the problem. When the fan was working, I could "hotwire" it (ignition off of course) and it would work. When the fan did not work I hotwired it and it did not work. I just did the refrigerator thing after I had it out in order to prove it was temperature related. Hope this helps someone. I know this is an old thread, but I just had to resurrect it. I'm currently having a similar problem. I got into my '98 Deville this evening and noticed that I didn't have any fan (no matter what speed or temp. I placed it on). Thank You soooo much Diesel for continuing to let everyone know your on going diagnoses with your problem. Too many times someone will have a problem and whether they get it fixed or not, we usually NEVER know because they do not tell what corrected their problem. Sometimes a person (I know I have before) can figure out their problem without ever having to post their question. I will check out the couple of suggestions that were given to you before I buy a blower motor. Thanks!!!! Link to comment Share on other sites More sharing options...
corkyd Posted December 12, 2006 Report Share Posted December 12, 2006 Also, most cars have a temp sensor in the A/C ducts.. if that quits, it will give you fits figuring out the problem. Link to comment Share on other sites More sharing options...
Ed Hall Posted December 12, 2006 Report Share Posted December 12, 2006 It's possible that the fan bearings need to be oiled. When it it cold, the old oil thickens and the fan doesn't run. When it gets warm, the oil becomes thinner and the fan turns. I also had this problem on mine and oiling the bearings fixed it. Link to comment Share on other sites More sharing options...
New Caddy Owner Posted December 20, 2006 Report Share Posted December 20, 2006 It turned out to be my blower motor. It was shot. Replaced with a new one and it's as good as new! Link to comment Share on other sites More sharing options...
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