A/C Surging

[ablediver]

Hey Folks,
Anybody experienced this one, let me know your solution. I have a 96' EB (5.8 AO4D). Here's the deal: I have the A/C on (MAX setting) and am accelerating, the output of the A/C decreases. When I level off the throttle or coast, the A/C increases. This is regardless of the fan speed. I don't think it's the blower, because there's no increase or decrease in any other setting but A/C. I've got this hunch that it's a vacuum line, but where I don't know. This 96' was a desert rat from AZ, and I wouldn't be surprised that a vacuum line cracked along the way. The vehicle has about 129K on it. I appreciate the reply.

Ablediver out

 

[wyo58]

I believe that the blend door motors on the HVAC system are vacuum operated, so when you accelerate vacuum goes down, when you let up vacuum goes up. I would look for a leak in one of those lines.

 

[ablediver]

OK. I'll check that out. Appreciate the tip.

Quick update: I cut/ pasted wyo58's response (above) into a browser search and it shows that, yep, it's more often than not, a vacuum leak and that particular thread came with a pic. of the offending part.

Thanks again, Bronco Crew

Ablediver out

 

[Tiha]

I think that is the recirc door out on the firewall, has a white vacuum line going to it. Right under the pass side hood hinge.

Under full throttle you have low vacuum and it doesn't hold the door open. Common problem. You can replace/add a vacuum canister will most likely solve the problem.

 

[Broncofan0]

Hey there,
First time posting here.

I had the same issue on my '95 351w. It was the white vacuum hose (sorry I don't have pics to share) in the engine bay that operates the blend door on the firewall. There was a large chunk missing on the bottom side of the hose. I spliced in a piece of new hose and viola!

Good luck!

 

[ablediver]

Thanks appreciate the tip. I'm working on it ,now

Ablediver out

 

[sgtdjl]

Hey Folks,
Anybody experienced this one, let me know your solution. I have a 96' EB (5.8 AO4D). Here's the deal: I have the A/C on (MAX setting) and am accelerating, the output of the A/C decreases. When I level off the throttle or coast, the A/C increases. This is regardless of the fan speed. I don't think it's the blower, because there's no increase or decrease in any other setting but A/C. I've got this hunch that it's a vacuum line, but where I don't know. This 96' was a desert rat from AZ, and I wouldn't be surprised that a vacuum line cracked along the way. The vehicle has about 129K on it. I appreciate the reply.

Ablediver out

That's nomal the compressor kicks off to give you more power to pass don

 

[ablediver]

Thanks appreciate the reply.


Ablediver out

 

[L\Bronco]

Thanks appreciate the tip. I'm working on it ,now

Ablediver out

Hey Ablediver, how did you make out with your A\C issue?
Just my 2 cents. If you don't find any leaks in the system,(which it likely is) there should be a vacuum check valve in the line that feeds the heater controls. if it fails, your cannister will lose vacuum as the engine loads. Here are a couple picts, good luck
Cheers

 

[ablediver]

Wow, I appreciate the diagram. It explains in detail how the system works. I haven't gotten to the system yet. That's for this weekend. Thanks again

Ablediver out

 

[L\Bronco]

Happy to help!
Cheers
Also, the vac reservoir for the A/C system should be a black plastic tank on the pass front inner fender above the wheel.

 

[Jimbo26]

....Also, the vac reservoir for the A/C system should be a black plastic tank on the pass front inner fender above the wheel.
[/QUOTE]
That late a model, yes. Go back a ways and there is the 'tomato juice' can in there instead.

 

[Ric330]

I've found 2 common causes of this problem. One is the white line that hooks to the vacuum motor mounted on the fender well under the right rear corner of the hood. The line deteriorates and leaks. Follow it as far back as it takes to find it to be in good condition and replace it from there to the motor. Also....the 3 port check valve located near the evaporator housing can be another cause of this problem. Google...Motorcraft YG193 and you'll see lots of places to buy it online.

 

[chrlsful]

agree w/#7. The increase (if normal amount) is due to feedback w/in the systems working together, not a problem/mistake.