Blower motor relay
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Cargo Master
Joined: Oct 2005
Posts: 2,298
Likes: 26
From: NJ
Blower motor relay
Apparently I've been banned from Oilburners mid-post, so being as I had some grand things typed I toss it out here in case it may help anyone.
Got back to this and got it done. I ran 14ga off the factory hot into the trigger for the relay, only went larger than necessary because it was easier to connect to the large factory wire. Did a unsealed butt connector on that crimped and followed up with liquid tape and heat shrink. 12ga from the relay to blower motor +12v, reusing the existing connector I pulled off the factory plug and crimped on the new wire. Used a Metripack 280 2 conductor plug to go to the fuse/relay box for easy disconnect. Heat shrink on the wires between plug and box and plug and blower motor.
New measurements:
Volts at blower, high: 13.84v
Volt drop blower high: 0.31v
Volts at blower low: 5.76v
Volt drop blower low: 0.07v
Amps high: 17.85
Amps low: 4.83
There is still room for improvement when I get to cleaning and adding grounds, the switch, etc. I'll get there. Voltage drop in teh cab is now down under 0.5v, from over 1v Anecdotally it seems to push a little more air. It's pulling 3.76 more amps so that's gotta be doing something. Still wish it did more, mainly for defrost. I may pull the blower and lube it and maybe check brushes and anything else I can figure. To do list is find the main ground and distribution spot in the cab and beef that up. I'll likely do either 8ga or 10ga straight from the battery as that's what I have handy and seems reasonable. 4ga would be way overkill.
Also found another thread on adding a blower relay. This guy did more or less the same thing, just not quite as neat an install IMO. BLOWER MOTOR RELAY MOD
Anyone else had a fairly significant voltage drop in the cab with the heater blower on? Mine drops abotu 1.5 volts (off the top of my head, will need to verify) with the blower on high. I would like more blower speed, keeping 14v+ in cab would probably help a bit. What's the fix? Just crusty old grounds? Inadequate factory wiring? Thinking of running 6ga or 8ga power and ground into the cab on a bus bar and distributing the the factory fuse box and any additional accessories from there. Maybe overkill, maybe there are better options, let me know. Also, where are the factory grounds and sizes so I can check and clean/repair/add where appropriate? Truck is an '86.
For what it's worth I picked up a clamp on ammeter and checked current draw. Just a cheapie, so it's within 3%-5% depending on where it falls in the range but it should be informative. After idling a bit after a start to charge up batteries, and with headlights on high beam, blower on high, radio on, the amp readings are as follows:
From alternator: 37.5A
4ga off batteries to solenoids/distribution to all load: 33.1A
Yellow to cab: 22.88A
Blower motor: 14.09A
130 amp 3g... Way overkill, seems like the 42A factory alternator was adequate and a 65 amp 1g certainly would be sufficient. Though the 3g can keep up with any normal or reasonable additional load in these trucks at idle where a 1g or 2g will not. Wish I had one of those mondo amp load test resistors to check max amps at idle and RPM.
I may do the blower relay this weekend. Should be quick and easy since wires are right on pass inner fender where my fuse/relay box is. I will measure voltage drop at the blower before and after. I'll likely do 12ga wire, one size larger than required for the load. Should solve the voltage drop to the rest of the cab and hopefully get a bit more CFM from the blower.
From alternator: 37.5A
4ga off batteries to solenoids/distribution to all load: 33.1A
Yellow to cab: 22.88A
Blower motor: 14.09A
130 amp 3g... Way overkill, seems like the 42A factory alternator was adequate and a 65 amp 1g certainly would be sufficient. Though the 3g can keep up with any normal or reasonable additional load in these trucks at idle where a 1g or 2g will not. Wish I had one of those mondo amp load test resistors to check max amps at idle and RPM.
I may do the blower relay this weekend. Should be quick and easy since wires are right on pass inner fender where my fuse/relay box is. I will measure voltage drop at the blower before and after. I'll likely do 12ga wire, one size larger than required for the load. Should solve the voltage drop to the rest of the cab and hopefully get a bit more CFM from the blower.
I started poking around on this. Oddly the wires are not intuitively colored. The ground is orange with black stripe, and the hot is black with orange stripe. The color scheme reverses to a more normal on the blower side of the plug. The ground is indeed through the resistor switch. Voltage at the blower plug varies from 11.96v on high to 5.53 on low, with 14.81 volts at the batteries (which seems on the high side). On high that's 2.85v less at blower than it could/should have. Directly measuring voltage drop I see 1.91v on high and .79v on low. So I'm losing another volt under load due to poor grounding. The main harness going to the blower motor appears to be 10ga, while the short leads from the motor itself appear to be 12ga.
I hooked up some short clip on test leads and blower speed didn't seem appreciably different, though it turns out they are only 18ga but have some pretty thick insulation which fooled me, so there was well over 1v drop through those. After that test I'm not expecting any huge gains, but will proceed to keep from overloading the old cab wiring and maybe get a minor increase in performance. I will use 12ga off the relay as it's only going a foot or two and I've already measured the load at 14.xx amps. Trying to figure out how I want to do the wiring to keep it clean and tidy so I'll ponder than for a bit then whip something up.
I hooked up some short clip on test leads and blower speed didn't seem appreciably different, though it turns out they are only 18ga but have some pretty thick insulation which fooled me, so there was well over 1v drop through those. After that test I'm not expecting any huge gains, but will proceed to keep from overloading the old cab wiring and maybe get a minor increase in performance. I will use 12ga off the relay as it's only going a foot or two and I've already measured the load at 14.xx amps. Trying to figure out how I want to do the wiring to keep it clean and tidy so I'll ponder than for a bit then whip something up.
Got back to this and got it done. I ran 14ga off the factory hot into the trigger for the relay, only went larger than necessary because it was easier to connect to the large factory wire. Did a unsealed butt connector on that crimped and followed up with liquid tape and heat shrink. 12ga from the relay to blower motor +12v, reusing the existing connector I pulled off the factory plug and crimped on the new wire. Used a Metripack 280 2 conductor plug to go to the fuse/relay box for easy disconnect. Heat shrink on the wires between plug and box and plug and blower motor.
New measurements:
Volts at blower, high: 13.84v
Volt drop blower high: 0.31v
Volts at blower low: 5.76v
Volt drop blower low: 0.07v
Amps high: 17.85
Amps low: 4.83
There is still room for improvement when I get to cleaning and adding grounds, the switch, etc. I'll get there. Voltage drop in teh cab is now down under 0.5v, from over 1v Anecdotally it seems to push a little more air. It's pulling 3.76 more amps so that's gotta be doing something. Still wish it did more, mainly for defrost. I may pull the blower and lube it and maybe check brushes and anything else I can figure. To do list is find the main ground and distribution spot in the cab and beef that up. I'll likely do either 8ga or 10ga straight from the battery as that's what I have handy and seems reasonable. 4ga would be way overkill.
Also found another thread on adding a blower relay. This guy did more or less the same thing, just not quite as neat an install IMO. BLOWER MOTOR RELAY MOD
Logistics Pro
Joined: Apr 2005
Posts: 4,221
Likes: 17
I experimented with this some myself, not solely the voltage drop, but the whole weak blower issue.
"Heater box full of leaves" No, it's clean.
"Crown Vic blower blows much better." No, new CV blower (with fan); works just as poorly as the old stock motor.
"New blower, old one is wore out" No, the CV blower was new.
"Voltage drop between switch to motor" No, jumpered the new CV blower straight to battery; including ground. No switches, nada. Blowed just as poorly as ever.
Conclusion: 7th gen Fords have crappy heaters.
Don't lose any sleep about being banned @ OB. Belonging to a clique is for teenagers.
"Heater box full of leaves" No, it's clean.
"Crown Vic blower blows much better." No, new CV blower (with fan); works just as poorly as the old stock motor.
"New blower, old one is wore out" No, the CV blower was new.
"Voltage drop between switch to motor" No, jumpered the new CV blower straight to battery; including ground. No switches, nada. Blowed just as poorly as ever.
Conclusion: 7th gen Fords have crappy heaters.
Don't lose any sleep about being banned @ OB. Belonging to a clique is for teenagers.
Thread Starter
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Cargo Master
Joined: Oct 2005
Posts: 2,298
Likes: 26
From: NJ
Crappy heaters indeed. While it seems to have made a marginal improvement there isn't exactly gale force winds coming from any of the vents. I recall reading about the crown vic motor, but I checked and it cross references to the same part number for aftermarket replacements. I figure that one's an old wives tale. I recall reading about different blower wheels though, that maybe the factory wheel in the trucks has excessive clearance in the housing. There may be wheels that fit better, but not sure where to start with that. Maybe measure my wheel and housing and look around a junkyard. Big issue for me is defroster performance.
Yeah the admins over at OB seem to have thin skin. My take is it's a few cops who want to be internet bullies too. Whatever, I've requested all my posts be deleted as I've contributed a lot over there so far as documentation, measurements, etc. in projects that I didn't have to do but took the extra time for the benefit of the community. Screw 'em, I don't want my efforts to be associated with that group.
Yeah the admins over at OB seem to have thin skin. My take is it's a few cops who want to be internet bullies too. Whatever, I've requested all my posts be deleted as I've contributed a lot over there so far as documentation, measurements, etc. in projects that I didn't have to do but took the extra time for the benefit of the community. Screw 'em, I don't want my efforts to be associated with that group.
Elder User
Joined: Feb 2008
Posts: 867
Likes: 3
From: North Bend
Firstly-- thanks for the good info guys!
I looked into this in a similar fashion a few years ago, and tested out the relay deal. For my setup, it blew significantly more air than it does now on all settings, especially HI. That said, something about the Ford design stinks. Dunno what though...
(I never got around to finishing and actually installing the relays, just tested the motor to direct battery mostly, and also ammeter tests)
One other thing that helps a lot is to just barely crack the windows when defrosting. It just lets all that air back out of the cab and gains a little velocity from the vents.
For me it helps about 30% better/faster.
I looked into this in a similar fashion a few years ago, and tested out the relay deal. For my setup, it blew significantly more air than it does now on all settings, especially HI. That said, something about the Ford design stinks. Dunno what though...
(I never got around to finishing and actually installing the relays, just tested the motor to direct battery mostly, and also ammeter tests)
One other thing that helps a lot is to just barely crack the windows when defrosting. It just lets all that air back out of the cab and gains a little velocity from the vents.
For me it helps about 30% better/faster.
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