Checking the FMTV fan system

[Floridianson]

I corrected the link. Just talked to Josh at FanClutch and they have this switch cheaper with the correct thread size. He said might have to rewire the ends but they said this one is in stock and cheaper. 90 bucks verse 130.00 for the 07950. The one they want to send is part # 1002-07393-32. Here is the pic of it.

 

[Floridianson]

Don't know if my truck is working right M1088? If the switch is a N/C then by unplugging the harness at the Temp switch/shutter stat then my fan comes on. I can still control the fan by using the fan switch on the dash and shut it off when warming up the truck or switch it on when over heating till I get it fixed.

Also I am starting to hate the FMTV's. I want my M915 back!!!!!!!!!!!!!!!!!!

 

[mkcoen]

Also I am starting to hate the FMTV's. I want my M915 back!!!!!!!!!!!!!!!!!!

Starting? I thought you started right after you bought it.

 

[Floridianson]

Here is a pic of the Alarmstat they sent me. A quick wire job and back on the road. It is NC and they said the correct size threads. I also picked up another new one from a bid/auction sight and it is 205* real cheap. Both are made by Kysor Medallion # 1002-07393.

Thread correcting that is a the number for 3/4 threads and the wrong one. Just my luck. Have to order the 07950 with 3/8 threads and pay the big bucks. Sorry I should have lesion to Tennmogger.

 

[1951M1078]

What lets the pressure out of the line when the switch turns off ? Or is their minor leak at the fan clutch ?

 

[TNriverjet]

What lets the pressure out of the line when the switch turns off ? Or is their minor leak at the fan clutch ?

There's an electric solinoid behind the passenger kick panel that dumps pressure based on input from the temp switch.

 

[1951M1078]

So the air pressure goes to the clutch fan first and when the valve. Then (when turned on by the temp switch) dumps the air to where ?

 

[Andyrv6av8r]

Air keeps the clutch disengaged. Temp switch closes the solenoid under the dash which shuts off the air supply and dumps pressure in the line through the solenoid exhaust. .

 

[TNriverjet]

I believe air is supplied to the valve behind the kick panel and sent on to the fan clutch. There are two air lines coming to that solinoid. I believe the larger line is the supply. When it dumps, pressure is released from this solenoid valve behind the panel.

 

[1951M1078]

Do I have this right /

When the valve is closed = #1 it lets air out from the clutch fan. (This lets the fan be turned by the belt drive )
#2 stops air from going to the clutch fan.

So it does two things ?

I was having a hard time with the (how does the air pressure get out)

 

[Andyrv6av8r]

Do I have this right /

When the valve is closed = #1 it lets air out from the clutch fan. (This lets the fan be turned by the belt drive )
#2 stops air from going to the clutch fan.

So it does two things ?

I was having a hard time with the (how does the air pressure get out)

Correct.

 

[1951M1078]

Where is the vent on the body of the valve ? Can't seem to find it ?

 

[Smike740]

The vent is located on the bottom center of the solenoid as it sits in the truck since its mounted upside down.

 

[1951M1078]

Vent ?

So when the center plunger is pulled up, it vents through the center of the plunger and out the hole in the photo ?

 

[Smike740]

Basically yes. The plunger seals on both ends depending on if voltage is applied or not. When voltage is applied the plunger pulls back and seals the vent, when voltage is disconnected the plunger prevents air from going to the clutch.

 

[wheelspinner]

Well, I had the same problem, took it apart to lube inspect, seemed to be finally working right,

And I did what several others have:

I stole TNRiverjet's photo, but the same problem. No where can I find one. Anyone have one? I need the fitting with the tiny microscopic threads that goes here.

 

[Awesomeness]

I did some checking on mine today, and there is some weirdness. Both the temp switch in the coolant tube and the one in the side of the thermostat housing are essentially the same. They are:

Coolant tube: TM-9A-230R/7


Thermostat Housing: TM-9A-230R-CANNON


According to Nason's website ( http://www.nasonptc.com/?q=product-tm ) these are the same switch, except for different cables. Namely, the part number breaks down to...
TM - Thermal Switch
9 - 3/8" NPT (Short) threads
A - SPST Normally Open (NO) circuit
230 - 230°F fixed set point
R - Rising set point direction
CANNON or /7 - Connector type, wire length

The one in the coolant tube turns the fan on, and it's supposed to be at 200°. However, I clearly have a 230° switch there. My fan clutch has been stuck in the fan-on position, so nobody probably ever noticed. The switch in the thermostat turns on the dash overheat warning light, and my dash light is always on because this switch for me is broke in the NC position. I think a GI mechanic put the wrong switch in the coolant tube, but never noticed because the fan is stuck on. (I'm replacing the clutch tomorrow.)

However, I went to look up the part in the 24P manual, and there is some more weird stuff (error?). Here's the picture, clearly showing the switch in the coolant tube labeled #3, and the one in the thermostat housing labeled #4.


However, when you scroll down a couple pages to the parts list, it says #3 is an air pressure alarm. #4 is correctly listed as the 230°F switch for the dash warning light (does this also do anything else, other than turn on that light? EDIT: I confirmed in the wiring diagram that all this switch does is light the water temp and master warning lights).


Since my switch in the coolant tube is Normally Open, I could use it to swap to the thermostat housing position (which is stuck NC, but is the same part), and then replace the one in the coolant tube with the correct 200°F part. Interestingly, the metal P36/P37 ID tags on the wires are correct. Are those put on by the mechanics when they install the parts, or do those come from the factory like that?

 

[wheelspinner]

https://www.mscdirect.com/webapp/wcs/stores/servlet/product/details/63033286

Was able to source an inexpensive direct replacement for the fragile little fitting and it works perfectly

 

[Mat65r]

can some one post a link for the air solenoid that engages the fan? i am looking for a replacement for my departments m1078.

 

[walshjuice]

Does anyone know if a fan clutch solenoid from a HMMWV will work for LMTV/FMTV's? I know there'll be some wiring and air line plumbing issues but I just want to know if it can work. Thanks!