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You can buy a whole new fan w/resistor for $100‘ish last time I checked on Amazon. Another one found here.

Ford OEM for $162 here.

They all have the resistor included.
 

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Or here:

I'd stick with the Motorcraft. I tried an aftermarket with no success. The blades were way out of balance.
 
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Discussion Starter · #24 ·
Yeah I'm going to go with the entire assembly either way. $227 for just the resistor is ridiculous.

I'll probably go with the OEM from rockauto or maybe the SVT upgrade (GT500 fan).
 

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Okay, went with the SVT fan. Same as the GT500, 7 blade. It should be here in about a week, so I'm curious to see if this was the issue all along.
I have the same fan in mine. It moves way more air.
 

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Discussion Starter · #28 ·
I have the same fan in mine. It moves way more air.
Nice! Yeah I figured it's the perfect time to upgrade. $245 shipped on CJPony parts. Not a bad deal.

Wow, huge shout out to CJPony parts. I ordered it on Sunday and they contacted me on Monday to let me know it was on back order and it wouldn't be until the 20th until they could get it. I said okay and asked them to add next day shipping to cut down on shipping time. I think it was like an extra $60-70 but the rep said he was having trouble getting it to charge and upgraded me to next day free of charge.

And today, it shows up! It took about 15 minutes to install it and I can confirm the fan does work now when the A/C is on. It stays on low all the time, no cycling. Just sitting at idle I got to 46F and it never went above that. Revving and holding to about 1,500 dipped it into the low 40's. The lowest I saw was 41F so... I'll take it lol.

I didn't test drive it because it was raining out but I sat in the car for about an hour. Never went below 46F at idle. It's not the best reading, but I'll take it. I'll know for sure when I test drive it tho.

Oh and I did check for resistance on the new resistor. The old one had no resistance and the new one does. So it was 100% confirmed bad.

I drove it after work today. It works great! I was frozen when I got out of the car lol. So this entire time it was just RTH and the fan was the issue.... Well, never a dull moment in the automotive world. Thanks everyone.

Well, it worked for a day... So its back to no A/C or just working when it wants too. I popped the hood once I got home and noticed the fan wasn't on (A/C was still enabled in the car) so I tapped on the relays and on comes the fan and the A/C compressor. I run down to o'reillys and get both relays. High and low fan speed and put them in. Nothing. Didn't change a thing but, I did notice one of them was arcing (the new low speed one). I kept hearing a zzzt, zzzt noise and noticed the low speed relay was shorting against something.

I shut it off, disconnected the battery and disassembled the fuse box (under hood, next to the passenger head light) hoping to find a burnt wire. I found nothing. No burn wires, no loose connectors etc. I put the relay back in reassembled. I never saw it short after that.

I had the manifold gauge set connected and I noticed it was at 25psi low side, 200 or so on the high side. Rock solid and steady when it does decide to work. According to R134a carts, that's about half of what It should be... So I'm not sure if I should overcharge it (I put in exactly 21oz) or if this is normal?

Either way, something is going on still with the low speed fan. I noticed the fan wants to come on, it'll move about an inch and stop then move again and stop. I'm back to square one.

To recap, what I've changed:

Hi / low pressure switch
Inside control panel (radio buttons, climate control buttons)
Fan assembly w/ resistor
Inside temp sensor next to the evaporator
Expansion valve
Evac'd, vacuumed down and recharged 3 times that I can remember.
Checked for leaks, found none.
Took off the clutch inspected it and shimmed the air gap according to the FSM

Its something electrical for sure, because when it does work it's super cold. The first (and only) day it did work It froze me out of the car.
 

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Agree its back to the fan not staying on that's your issue. Since the new fan worked normally until now, focus on the new fan. Pull it back out. Check the resistor on the new fan to make sure it didn't burn up. Check for continuity across the resistor. If its burned out, how does the fan plug look? When I changed my fan a few years ago I noticed significant overheating of the fan plug. If there is excessive resistance due to poor contact, it could be what burned out the old fan resistor. As for the pressures, here's the chart I use. It also factors in humidity. Since you weighed it in, I'd leave the charge alone.
 

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Discussion Starter · #30 ·
I checked this morning with it cold. Started it up and turned the A/C on. The low speed fan works fine. I'm really curious as to why the low speed fan relay was arcing and what it was arcing on.

When I changed the fan I inspected the connectors for melting. All was good.

Here are some strange things I have noticed so far and or yesterday:

Idle will surge or dip real low when the A/C comes on sometimes. This is random tho, sometimes it almost stalls it out and sometimes you can't even notice it. This goes for driving too. When it's acting up you can feel the whole car surge (kind like abruptly lifting off the accelerator). Its like it needs a ton of power to function but I'm not sure if it's the high speed fan or A/C compressor.

It seems to act up more when the car is moving. If I'm just sitting it will usually work which makes it almost impossible to diagnose, but once I move it's a 50/50 change if it will. Last night for example, it worked off and on but when parked it and went to set up the manifold gauge it was normal...

After it straight up refused to work while I was driving, I sat in the car for about 15 minutes after I confirmed pressures and what not and it was ice cold. No idle fluctuations or anything. It was perfect.
 

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At this point I strongly suggest you take it to a reputable shop that is familiar with these vehicles and have it checked over. There's only so much we can help with via forums, especially when it comes to A/C systems. You've already put a lot of time and money in to trying to resolve the A/C along with the transmission shifting issues.
 
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Discussion Starter · #32 ·
Agreed, and I'm almost out of patience at this point. I took it to my brother in laws garage this evening. He runs a very small auto repair shop (but doesn't do A/C stuff) although is very good with a wrench. So we both disconnected, probed and checked voltage and or continuity of every connector we came across.

No burn wires anywhere, nothing melted and voltages were all on point and within spec. And I mean everything, fuse box was taken apart, PCM taken out etc. I even bought two new relays (Fuel pump and AC clutch) thinking that might be it. Nothing. So after we spend hours doing this, we get it back together and test it. Magically it works as it always does when it's stationary.

Not 3 miles down the road, straight hot air. We take it back and leave it running to see if we can see and or find anything since it is now acting up. No low speed fan at all. We start wiggling connectors and shaking harness's etc to see if we can get any response. Nothing...

Inside the car, nothing burnt or melted. Tapping or moving wire harness's around does nothing. Short of taking the PCM apart, we are both at a loss. When it's cold the A/C works fine however, which would mean an electrical issue I would think.

I forgot to add. The fan resistor was taken out as well and checked again, all good.

Random question. Where is the CCRM on a 2010 Mustang GT? It seems that is the source of my issue but I have no idea where it is. I can't find a picture or anything and I see no wires running to the passenger side fender well like the new edge.
 

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You can dig through all these wiring diagrams:
and the Climate Control Diagnostic section:
 

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Discussion Starter · #34 ·
I can't seem to find anything about a CCRM on this car at all. But, I did find this:



If I'm looking at this correctly, the PCM controls the fan speeds. I'm going to assume the PCM grounds either the low or high, sends power to the relay then the fan.

Seeing how the wires from the PCM to the BEC are good and the wires from the BEC to the fan are good, it has to be a PCM problem right?

I'm to an electrical master by any means, but I have done some SMD soldering before. Do you think its possible to open the PCM up and inspect inside?

download.png
 

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Discussion Starter · #35 · (Edited)
This graph is not for a 2010 and up ^^

So, I made some progress today. I yanked the SJB and checked all the connections. I found one connector with some greenies in it so I cleaned it out real good with some 91% iso and a tooth brush. Other than that, the SJB looked fantastic.

I pulled the PCM again with the intent of opening it up. But, I don't have anything decent to reseal it up with, so I passed on that but all the pins were good and nothing was burnt or melted. I checked any and all wires on the PJB next to the passenger headlight again but this time solo. I checked resistance on the fan wires, grounds, etc and everything came back good. I reinstalled everything and went for a drive.

It worked fantastic. I drove for about 10 miles or so, semi spirited to get it nice and warmed up. It worked great the entire time and was freezing cold. I get it back home, pop the hood to verify everything is legit and what do you know... it starts to flake out. But, again I noticed arcing in and around the low speed fan relay. I quickly yanked it out, and replaced it with the factory relay (with it still running) and everything was back to normal. I put the new relay back in after about 2-3 minutes and it was normal as well.

After about 5 minutes, it started again. I noticed the A/C clutch the most because it was louder but it was switching off and on in unison with the arcing relay. Same for the low speed fan. I yanked the low speed fan again and nothing was on. No A/C and no low speed fan. A few minutes later the high speed fan kicks on.

So, it's either:
  • A very weak relay
  • The arcing is coming in contact with the A/C clutch wire causing it to switch off and on erratically
  • The low speed fan and A/C only worth together and not independently.
  • Something else?

Again, all the wires and connectors looked great. Nothing was loose burnt or green. I've never heard of a relay overheating, but I think that might just be the issue.

Or maybe coat the bottom of the fuse box with dielectric grease?
 

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Discussion Starter · #36 · (Edited)
Well... I think I found my issue or at least an issue. The FSM and relay info for a 2005 and 2011 show a 40A relay for the low and high speed relays (see pic, that's from the 2011) yet I'm running 30A relays that I bought from O'reillys... wth lol.

Edit:
Nope, 40amp relays installed and it started acting up again.

I broke out the multimeter again and started back probing and checking things again. I even took the lid off the PCM to check in there. Nothing suspect.

I let it idle for over an hour and it never acted up. I drove it not 2 miles down the road, it started acting up and I came back home. I saw the fan go off for maybe 20-30 seconds then back on.

Again, I let it sit and idle for 30 minutes this time. It was perfect.... This car is cursed man.
 

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Well... I think I found my issue or at least an issue. The FSM and relay info for a 2005 and 2011 show a 40A relay for the low and high speed relays (see pic, that's from the 2011) yet I'm running 30A relays that I bought from O'reillys... wth lol.

Edit:
Nope, 40amp relays installed and it started acting up again.

I broke out the multimeter again and started back probing and checking things again. I even took the lid off the PCM to check in there. Nothing suspect.

I let it idle for over an hour and it never acted up. I drove it not 2 miles down the road, it started acting up and I came back home. I saw the fan go off for maybe 20-30 seconds then back on.

Again, I let it sit and idle for 30 minutes this time. It was perfect.... This car is cursed man.
Wow.....yours sounds almost just like mine. And yes, I have a 2010 also. I even changed the compressor and receiver/dryer to be sure so don't waste your time and money on that. Just today I installed a remote switch in the ac relay spot so I can just manually turn the compressor on and off from inside the car. Not sure what else to do. I even had it at two different shops to no avail. One of which was the local Ford dealer who tinkered with it for 3 days and finally gave up.
 

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Shoot Brian (Fordtechmakuloco) an email to see if he has any suggestions.
Brian Laskowski <[email protected]>
 
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Discussion Starter · #39 ·
Wow.....yours sounds almost just like mine. And yes, I have a 2010 also. I even changed the compressor and receiver/dryer to be sure so don't waste your time and money on that. Just today I installed a remote switch in the ac relay spot so I can just manually turn the compressor on and off from inside the car. Not sure what else to do. I even had it at two different shops to no avail. One of which was the local Ford dealer who tinkered with it for 3 days and finally gave up.
Yeah, it's so hard trying to diagnose this thing because it's so random. I can start the car up and just let it idle for an hour and it works just fine. Driving down the road it starts to act up. I get it back stationary to trouble shoot and all of the sudden it works again.

I've been over the diagrams, had the relay (PJB) apart and out numerous times. New relays, checked resistance on ever wire I could.

I've even noticed running with the A/C off the low speed fan still acts up. So it has to be something related to the low speed fan but at this point I'm not sure what. Other than something internally wrong with the PCM I'm at a loss. Even that tho is kind of a stretch. Everything PCM related works except for the low speed fan? That just doesn't make any sense.
 

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Yeah, that was the last thing the Ford dealer said to me...they were pretty sure something was triggering the fan to turn off which was then causing the compressor to turn off. I also replaced the fan w/resistor which of course didn't help.
 
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