AC issues and attempts to correct them
07-08-2010, 10:55 PM
#1
Senior Member
Thread Starter
AC issues and attempts to correct them
OK, I've been dealing with issues in the AC of my truck. Mine is a 1994 F150 XLT. It only has 76+K miles but it does have some age on all the components.
The symptoms are that the air alternates blowing out of the vents (cold/cool) and then switching to the defrost vents (mostly warmer air). Also, the Max AC only blows for a little while before it stops blowing out of the vents (I'm not sure where the air goes when it stops blowing out of the vents).
The problem appears to be related to the loss of vacuum when the engine is under load (like the old cars used to do with the windshield wipers). I rigged up a vacuum gauge to see what was going on.
Above is the gauge connection at the black hose that goes to the AC controls
Above is the vacuum at idle (the same at the red or black hose connections)
Above is the vacuum at the black hose after 10 seconds of shutting off the engine. No vacuum reserve in the tank.
I went to the junk yard (it was hellishly hot!) and after trudging for a while baking under the early afternoon sun, I finally found a '95 F150 with the can in it. I removed the can and bought it (a little over $10). Anyway, I changed it with mine and it was hardly any better
.
I actually tried sucking some vacuum out of the nipples in the cans, and sure enough, both leaked...
I figured that I could further test the situation by adding a little check valve on the red hose side (the manifold vacuum source) so the air could not flow back into the can when the engine was making no vacuum.
I tried driving and using the AC. It worked considerably better than without the check valve, but it still would lose vacuum when the engine was not making vacuum.. I think that there must be another vacuum leak somewhere, but I don't know where to look first. The sticker under the hood shows a schematic of the vacuum lines arrangement. Take a look at the black hose that comes out of the can. It appears to go to some junction or component where it and the green hose go in and come out again to go the EGR/EVR little symbol.. I could not locate it readily under the hood. I hope it's not behind the motor
Anyway, this is the schematic, I've labeled the mystery component. Anybody know where and what it is? I think I'm getting closer to solving the AC puzzle, and none too soon.. It's almost 100° here during the day and we expect no break on these temps for at least several more days...
Please feel free to help out with info or other input.
Thanks
And yes, I already fixed the disintegrating white hose that goes to the solenoid near the fan motor under the hood in the pax side....
The symptoms are that the air alternates blowing out of the vents (cold/cool) and then switching to the defrost vents (mostly warmer air). Also, the Max AC only blows for a little while before it stops blowing out of the vents (I'm not sure where the air goes when it stops blowing out of the vents).
The problem appears to be related to the loss of vacuum when the engine is under load (like the old cars used to do with the windshield wipers). I rigged up a vacuum gauge to see what was going on.
Above is the gauge connection at the black hose that goes to the AC controls
Above is the vacuum at idle (the same at the red or black hose connections)
Above is the vacuum at the black hose after 10 seconds of shutting off the engine. No vacuum reserve in the tank.
I went to the junk yard (it was hellishly hot!) and after trudging for a while baking under the early afternoon sun, I finally found a '95 F150 with the can in it. I removed the can and bought it (a little over $10). Anyway, I changed it with mine and it was hardly any better
.I actually tried sucking some vacuum out of the nipples in the cans, and sure enough, both leaked...
I figured that I could further test the situation by adding a little check valve on the red hose side (the manifold vacuum source) so the air could not flow back into the can when the engine was making no vacuum.
I tried driving and using the AC. It worked considerably better than without the check valve, but it still would lose vacuum when the engine was not making vacuum.. I think that there must be another vacuum leak somewhere, but I don't know where to look first. The sticker under the hood shows a schematic of the vacuum lines arrangement. Take a look at the black hose that comes out of the can. It appears to go to some junction or component where it and the green hose go in and come out again to go the EGR/EVR little symbol.. I could not locate it readily under the hood. I hope it's not behind the motor
Anyway, this is the schematic, I've labeled the mystery component. Anybody know where and what it is? I think I'm getting closer to solving the AC puzzle, and none too soon.. It's almost 100° here during the day and we expect no break on these temps for at least several more days...
Please feel free to help out with info or other input.
Thanks
And yes, I already fixed the disintegrating white hose that goes to the solenoid near the fan motor under the hood in the pax side....
Last edited by blade z51; 07-08-2010 at 11:16 PM.
The following users liked this post:
brunstribe (07-09-2012)
07-09-2010, 12:16 AM
#2
Are you sure your blend door solenoid is holding vacuum itself? It's rare for the diaphragms to go in them but it does happen. FYI I don't have that can and have no issues....I don't have any of those solenoids actually.
The following users liked this post:
brunstribe (07-09-2012)
07-09-2010, 12:28 AM
#3
Junior Member
Check the vac line running to the blend door (passenger side against the firewall. White plastic line.) Sorry, I should read your entire post before comenting, I will go sit in a corner now. Good luck with it.
Last edited by wuzslo; 07-09-2010 at 12:32 AM.
The following users liked this post:
brunstribe (07-09-2012)
The following users liked this post:
brunstribe (07-09-2012)
07-09-2010, 10:52 AM
#5
Senior Member
Thread Starter
I have not checked for leaks under the dash yet...
The following users liked this post:
brunstribe (07-09-2012)
07-09-2010, 12:23 PM
#6
Senior Member
Thread Starter
Almost success....
I still have not looked under the dashboard yet. However, I looked again under the hood to see if I could reason out the vacuum arrangement. Here is the vacuum that appears to go to the AC.
While touching and moving the hoses I discovered another vacuum leak source. See the picture below....
I pulled the little rubber boot off the air plenum and after some effort I got the piece of tube off (it was broken flush with the top of the rubber boot). I then cut the remaining tube in half and used a bit of rubber hose to increase the length of the line and reinstalled it.
I was very hopeful that this would be the answer to the problem. I test drove it and it appeared to work much better. The "Max AC" setting actually worked continuously while I drove to the store. However, while returning home I drove up a very steep hill about 1/4 mile long. About half way up, the air stopped coming out of the vents and worse yet, the engine bogged down quite a bit. This was with the setting on "Max AC". I switched back to the regular AC setting and crested the hill about the same time. The AC started blowing out of the vents again and the engine pulled fine. Of course, by them I was over the steepest part of the hill, although still pulling slightly uphill.
I'm not sure what happened there when the engine bogged down so much. I need to return to the hill and see if it bogs down without the AC on "Max" and under different settings. Also, the air is not blowing really cold so I might need to have the freon level checked as well....
Update
I took it to a shop and had the AC re-charged. The engine now seems to feel more the load of the AC and the AC blows colder. I tried the steep hill again without AC and it pulled up it OK. I still have the issue of the vents switching to defrost under the heaviest load to the engine, but much less than before. I think I'll consider the AC "fixed" and try to quit messing with it any more unless it degrades in performance again
While touching and moving the hoses I discovered another vacuum leak source. See the picture below....
I pulled the little rubber boot off the air plenum and after some effort I got the piece of tube off (it was broken flush with the top of the rubber boot). I then cut the remaining tube in half and used a bit of rubber hose to increase the length of the line and reinstalled it.
I was very hopeful that this would be the answer to the problem. I test drove it and it appeared to work much better. The "Max AC" setting actually worked continuously while I drove to the store. However, while returning home I drove up a very steep hill about 1/4 mile long. About half way up, the air stopped coming out of the vents and worse yet, the engine bogged down quite a bit. This was with the setting on "Max AC". I switched back to the regular AC setting and crested the hill about the same time. The AC started blowing out of the vents again and the engine pulled fine. Of course, by them I was over the steepest part of the hill, although still pulling slightly uphill.
I'm not sure what happened there when the engine bogged down so much. I need to return to the hill and see if it bogs down without the AC on "Max" and under different settings. Also, the air is not blowing really cold so I might need to have the freon level checked as well....
Update
I took it to a shop and had the AC re-charged. The engine now seems to feel more the load of the AC and the AC blows colder. I tried the steep hill again without AC and it pulled up it OK. I still have the issue of the vents switching to defrost under the heaviest load to the engine, but much less than before. I think I'll consider the AC "fixed" and try to quit messing with it any more unless it degrades in performance again
Last edited by blade z51; 07-09-2010 at 01:05 PM.
The following users liked this post:
brunstribe (07-09-2012)