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Since it is summer time and we do not yet have a thread up on this subject I thought I would start one. The main benefit of doing this mod is that you get colder air out of the AC as you are not trying to cool down air that has been heated up by the heater core. You are simply shutting off the flow or coolant to the heater core using a valve controlled by a vacuum source. I will also put this in the Library to save once we get a good thread completed on it.

There are a few variations of this that give you some options that we can lay out in this thread. A basic set of directions is:

I have instructions that I came across some time ago. I do not know where I got them but here they are:
A/C heater core shutoff mod

This mod will stop the flow of hot water through the heater core when the AC controls are in the MAX setting and the OFF position providing cooler temps and preventing the hot pocket of air down by your feet. I went to NAPA and asked for the 'hot water shut off valve' from a 1990 Ford Ranger with a 4.0 V-6, I also got 4 - 5/8 hose clamps, a couple feet of 1/8" vacuum line and a 1/8" plastic "T" for the vacuum line. To begin the install loosen the cap on the radiator overfill to remove pressure from the system (do this while the engine is cool). On the passenger side of the engine compartment there are two 5/8" hoses that come from the firewall and continue to the engine, these are the heater hoses. Cut the hose closest to the drivers side (It doesn't really matter where, I did mine about 6 inches after the firewall). Then holding the 'shut off valve' with the vacuum controller towards the passenger side install the portion of the heater hose coming from the cab to the top left nipple on the 'shut off valve'. Tighten the clamp. Install the portion of the heater hose coming from the engine to the top right nipple and tighten the clamp. Next cut the heater hose closest to the pass side in the same location as the previous. Install the portion coming from the cab on the lower left nipple, tighten the clamp. Now install the portion going to the engine on the lower right and tighten the clamp. Measure out how much of the 1/8" vacuum line you need to reach from the bottom of the vacuum canister on the shut off valve to the white vacuum line on the pass side that goes to the vacuum operated door underneath the pass side cowl. Cut that white vacuum line and splice in the 1/8" plastic "T". Then run the 1/8" vacuum line you measured out from that plastic "T" to the nipple on the bottom of the vacuum canister on the shut off valve. It sounds more complicated than it is. Once you do it the job will seem real simple.
 

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Discussion Starter #2
I did mine a little differently because I wanted to shut off the flow of coolant to the heater core in Max AC, AC and Vent. To accomplish that I tapped into the blue line under the glovebox inside the cab for the vacuum source. I have found that lets the vent position be much more useful the air temp from vent is not getting heated by the heater core. The only downside is that I have to unplug the vac line in the winter so that I can get heat in the vent position. Floor and defrost do work normally with the vac line connected.
 

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Discussion Starter #4 (Edited)

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if you just block the hose arnt you blocking the return flow to the head?
 

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PSN Mega Miler
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Ive read of doing this since I got by truck a few years ago but my a/c is so cold now (38 degrees with it 90 outside) I cant see a reason to do it personally on my truck. Heck if anything I bet my a/c is cooling the engine some :D

Does seem like ford had a reason to keep it flowing though and the return flow you mentioned could be it. I dont remember how the hoses route thru it right off the bat.
 

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Discussion Starter #7
Ive read of doing this since I got by truck a few years ago but my a/c is so cold now (38 degrees with it 90 outside) I cant see a reason to do it personally on my truck. Heck if anything I bet my a/c is cooling the engine some :D

Does seem like ford had a reason to keep it flowing though and the return flow you mentioned could be it. I dont remember how the hoses route thru it right off the bat.
On my truck I would do the mod for the sake of how much better it makes using the vent setting if nothing else. It makes vent useful on a 60-70 deg day instead of a heat function.
 

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Tom, you've done this mod? When does it make the most difference?? DID it make a big difference?

On Edit:Guess that answered my question! LOL

How much cooler did it make everything?
 

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Another reason to block off the heater core, besides allowing the A/C to cool unheated air, is so that you can use the 'vent' position in the fall and spring and get cool outside air so that you don't have to run the A/C. I used to take a C clamp and squeeze shut the line to the heater core, which worked fine, but if it was hot in the daytime and cool at night I was under the hood more times than I cared for.

In a galaxy far away and a website from another time a guy going by hutchinaugusta came up with a fully automatic method of shutting off the flow to the heater core...read the thread here (scroll down to ExcursionPSD - post number 6) and then see Hutch's pictures here. Hutch had a very good description of how he did it, but I was unable to find it...:shrug:...maybe someone else can do a better search over there...

Tim

PS...I'm gonna have to learn to type faster! Tom, and others, beat me by 6 minutes...
 

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Discussion Starter #10
I would guess it takes 5-10 degrees off the AC setting and maybe 20 on vent. It is a easy to do mod that works. I used to hate the vent setting unless it was cold but now you can use it at times on those inbetween days when before it meant all the noise of windows down or running the AC. I hope some other will post up results as well.

Tim, it's sad that all the good information from back in the day at that site is basically lost as it cannot be found. FYI I am surely not taking credit for this mod just sharing some info from the old days for the newbies. I might have been the one to figure out the blue line is about it.

I came across this from 5 years ago. A/C Mod time - Diesel Forum - TheDieselStop.com Lots of good discussion.
 

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Tim, is sad that all the good information from back in the day at that site is basically lost as it cannot be found.
I sure agree with that! Your post reminded me of the old stuff and I went over there looking...kind of a blast from the past...and yeah, lots of info for folks just getting started...you're to be commended!:bowfast:


Tim
 

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PSN Mega Miler
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I guess someone did the mod on mine already or something because mine blows cool air on the vent setting, well cool as the outside air is.

Rainy weather lets up I'll poke around on mine and see if I can tell if anythings been done to it.
 

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SLOW LEARNER
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I snapped a few of mine. I used the early 90's Ford minivan valve. Its been some years since I did it so I don't recall the differences I noticed.





 

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Terminator Nation
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The use of the Early 90's Ranger V-6 valve allows bypassing the heater line back to the engine. I never had a valve failure and its been in there since the mod was first publicized back when.

I did not cut the vacuum line to insert the plastic tee. I just took the stock line and put the tee into the end, put a short piece of the new tubing on the tee and hooked it to the new valve, and ran new tubing back to the original valve. There's a picture of it in my sig photos.
 

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Discussion Starter #15 (Edited)
Photos were reposted here since webshots took the original ones away.
Heater shut off valve - Page 3 - PowerStrokeNation : Ford Powerstroke Diesel Forum



This is mine. The hose on the right where you can read the words Gates goes to the hose that comes off the head. The other hose goes to the top of the water pump. You can see the flow arrow in the picture.




A closer look. Since I used the blue line in the winter I just pull the vacuum line off the actuator and plug it into the rod that show in the picture. Then it all works just like the factory made it. I like these valves that are more metal. I think the plastic ones look like they might break. A two port valve could also be used here. I just chose this back when I did this mod.


I used the blue line under the dash which cut off the flow of coolant in vent, AC, max AC. I unplugged the clear looking connector from the actuator and put that on a tee. I then used vacuum to run from the actuator to my valve under the hood. The tee is spliced into that line. I did not have to cut anything by doing it that way.
 

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Discussion Starter #17
If you really want to get fancy beyond Allen and his hose pinchoff pliers Dieselsite has a electric vacuum control so that you can control your heater hose valve at the touch of a switch. Cold Rush- Upgrade to 6.0L and 7.3L Max That just stuff Allen under the hood like trunk monkey.
 

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Just did mine last weekend and it seemed to help. Ford place ordered wrong valve for me so I ran to parts store and jst picked that was the correct size. I dont even know what it was for. One post said to use a 1/8 tee on white hose under glovebox for vac line but the 1/8 tee didnt fit very well. I have it half arse stuck together for now and it does work but i need to find a smaller T i think
 
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