Zero Knievel Posted June 22 Posted June 22 On the pickup truck, three times so far the blower motor stopped working. Not while in operation, but from when the truck turns on. In each case, at some random time, the blower resumes operation. The compressor is irrelevant here. It stopped working long ago, and I disconnected it. So far, I’ve accessed the controls and see nothing wrong…checking terminals and reconnecting with dielectric grease on the contacts. I’ve switched the air on and off multiple times, varying delays, and I got the problem to repeat. Suspecting maybe the blower motor was failing, I manually jumped the blower motor off of a spare motorcycle battery. The motor works. Reconnecting things, the system works, and I’ve been unable to reproduce the problem. I know it may be possible that a coil on the fan motor has failed, and only if the fan stops in the “right” position, it’s resting on the dead coil. Not sure how to eliminate that without taking apart the fan motor and checking coils manually…if that’s even possible as it may be a sealed unit. Last are the relays. There may be as many as three that in some way relate to the AC system. Every fuse is intact. Not sure how to test a relay without knowing the layout of the terminals. When the system turns off (blower working), there is a distinctive CLICK from the box where the relays are located. I believe there is no sound when the system is turned off but the blower isn’t working. I see no evidence of damaged wires. Do relays have intermittent failures? I’ve yet to see the problem happen when the blower is running. Every time, the blower came back on with the system already turned on. I got the problem to repeat in the garage with the engine off and at a controlled temperature. So, no change in temperature or vibration from the motor. I could see if replacement relays can be sourced, but it would be guessing at the cause. Anything else I should check? Quote
tomek Posted June 22 Posted June 22 13 minutes ago, Zero Knievel said: The compressor is irrelevant here. It stopped working long ago, and I disconnected it. I’ve switched the air on and off multiple times, I need head steering damper. 1 Quote
Zero Knievel Posted June 22 Author Posted June 22 The compressor is only for the cooling…it tore up, and to prevent the mechanism seizing, I disconnected the pressure switch that makes the clutch cycles on and off. The cost of fixing it…again…wasn’t worth it. Quote
SwampNut Posted June 22 Posted June 22 1 hour ago, Zero Knievel said: Do relays have intermittent failures? Every item in the chain here can have an intermittent failure. Also you didn't say what vehicle, and "the pickup truck" is a very vague recollection. I know I've seen it, don't remember details. Are the controls seemingly all analog? When it fails I assume you've run through all potential settings from off-low-high to all the other switches? Your troubleshooting is probably going to have to include testing power at all the various places while the problem is happening. You could hang wires out of those spots for easy access with a meter when it fails. Quote
Zero Knievel Posted June 22 Author Posted June 22 It’s a 1998 Mazda B3000. Analog AC system. I would suspect a loose wire if the fan started and stopped during operation, but it only happens when the system first turns on…be that from switching it out of OFF or starting the truck with the system already on. A loose wire wouldn’t be a likely culprit when parked in a garage. A bad analog switch should be consistent…and heaven knows I’ve worked it enough to find out if it’s failed. I might just have to see if the relays under the hood are replaceable. Quote
blackhawkxx Posted June 22 Posted June 22 (edited) You do know there is a blower resistor in the system right? Usually they start failing only on one or two fan speeds but I guess it may be possible that it or the connection to be failing. I'm not saying that is your problem but another place to look. https://www.autozone.com/cooling-heating-and-climate-control/blower-motor-resistor/p/duralast-hvac-blower-motor-resistor-ja1506/200888_0_0 Edited June 22 by blackhawkxx 1 Quote
SwampNut Posted June 22 Posted June 22 30 minutes ago, Zero Knievel said: but it only happens when the system first turns on…be that from switching it out of OFF or starting the truck with the system already on. I thought it was more random than that. So it doesn't always happen if you switch it off then on, but only happens when switched on? Quote
Zero Knievel Posted June 22 Author Posted June 22 4 hours ago, SwampNut said: I thought it was more random than that. So it doesn't always happen if you switch it off then on, but only happens when switched on? It only happens, at random times…and only a total of 4 so far…when the blower goes from off to on. Be it switching to a mode from off that turns on the blower OR starting the truck with the blower already in the on condition. I’ve never seen the blower stop once it is in operation. Quote
rockmeupto125 Posted June 23 Posted June 23 So closing a circuit, either by turning the ignition switch on or moving the fan switch to on, is the circumstance upon which the circuit either functions or fails to function. Conditions have to be meet for electricity to flow. Think of an arc welder. On a vehicle of that age, I would suspect an aging ground connection for that circuit. Quote
Zero Knievel Posted June 23 Author Posted June 23 (edited) 1 hour ago, rockmeupto125 said: So closing a circuit, either by turning the ignition switch on or moving the fan switch to on, is the circumstance upon which the circuit either functions or fails to function. Conditions have to be meet for electricity to flow. Think of an arc welder. On a vehicle of that age, I would suspect an aging ground connection for that circuit. Gad, I hope not...trying to find it would be a pain. Of course, IF it was doing this when it was already running, I would have good cause to suspect something like this. I've taken pics of the two relays dealing with the A/C system. I might see about replacing them prophylactically. If I can get the error to repeat, I may fiddle with wires and see if it makes it come on. So far, that hasn't worked. https://www.amazon.com/dp/B0D11PZM2L/?coliid=I2F1B83S1JJ1X&colid=O6UAJ0EU8IZ1&ref_=list_c_wl_lv_ov_lig_dp_it&th=1 https://www.amazon.com/dp/B0BN3GTJPT/?coliid=I1VIOIPPB3SY59&colid=O6UAJ0EU8IZ1&psc=1&ref_=list_c_wl_lv_ov_lig_dp_it Edited June 23 by Zero Knievel Quote
superhawk996 Posted June 23 Posted June 23 95% it's the motor. To confirm, next time it doesn't fire up give the motor a whack while it's powered up. If it starts then you'll know for sure. Quote
Zero Knievel Posted June 23 Author Posted June 23 Just now, superhawk996 said: 95% it's the motor. To confirm, next time it doesn't fire up give the motor a whack while it's powered up. If it starts then you'll know for sure. I tried that with no result. I will certainly try again. Too bad I can't move the blower when it's buttoned up...that I know of. It would be an easy way to eliminate the motor as the culprit. Quote
tomek Posted June 23 Posted June 23 3 hours ago, superhawk996 said: 95% it's the motor. To confirm, next time it doesn't fire up give the motor a whack while it's powered up. If it starts then you'll know for sure. Yea, I was just gonna post it. Give it all good fashion whack. Quote
tomek Posted June 23 Posted June 23 (edited) Can you hook up multimeter to the motor, and drive around to see if it is powered when goes kaput? And if it doesn't get juice just work backwards of current path. Edited June 23 by tomek Quote
Zero Knievel Posted June 23 Author Posted June 23 16 minutes ago, tomek said: Can you hook up multimeter to the motor, and drive around to see if it is powered when goes kaput? And if it doesn't get juice just work backwards of current path. That would be...impractical. Since I can repeat the problem when parked, it would be just as easy to keep flicking the switch until it repeats. Quote
SwampNut Posted June 23 Posted June 23 Not impractical, this is what I've done. On 6/22/2025 at 8:42 AM, SwampNut said: Your troubleshooting is probably going to have to include testing power at all the various places while the problem is happening. You could hang wires out of those spots for easy access with a meter when it fails. Quote
jon haney Posted June 23 Posted June 23 New Blower motor from RockAuto runs from $18 to 49. Additional $10 for the blower motor module. Blower motor relay is $8.50 to 22. How much time have you spent on this already? 1 1 Quote
jon haney Posted June 23 Posted June 23 32 minutes ago, XXitanium said: BTDT LOL. I had to Google that one. 1 Quote
tomek Posted June 23 Posted June 23 4 hours ago, Zero Knievel said: That would be...impractical. Since I can repeat the problem when parked, it would be just as easy to keep flicking the switch until it repeats. Well, I predict 5 pages. 😁 Quote
SwampNut Posted June 24 Posted June 24 4 hours ago, jon haney said: LOL. I had to Google that one. Bottom top dead top. It's the piston position on a Delorean with a flux capacitor at 88 MPH. Quote
Zero Knievel Posted June 25 Author Posted June 25 Success. I had to dismount the fan motor then keep switching off and on until it stopped working. Gently started to rotate fan cage, and it started right up. Bad motor. I can pick up a replacement at AutoZone, and I don't need to worry about the relay because I heard it clicking when the fan wasn't engaging. Only issue is that the OEM gasket between the motor and housing isn't available...so I need a replacement material. I suppose a strip of foam rubber can do the job. Quote
blackhawkxx Posted June 25 Posted June 25 6 hours ago, Zero Knievel said: Success. I had to dismount the fan motor then keep switching off and on until it stopped working. Gently started to rotate fan cage, and it started right up. Bad motor. I can pick up a replacement at AutoZone, and I don't need to worry about the relay because I heard it clicking when the fan wasn't engaging. Only issue is that the OEM gasket between the motor and housing isn't available...so I need a replacement material. I suppose a strip of foam rubber can do the job. Make sure you try the new motor just like you did with the old one before mounting it. Quote
superhawk996 Posted July 2 Posted July 2 On 6/25/2025 at 4:57 AM, Zero Knievel said: I can pick up a replacement at AutoZone I hope it'll be OEM like you demand for the AC parts. Quote
Recommended Posts
Join the conversation
You can post now and register later. If you have an account, sign in now to post with your account.
Note: Your post will require moderator approval before it will be visible.