99 F-250 SD XLT V-10

The A/C in my truck worked very well. It started going out on me so I recharged it and felt that I had solved the problem. Every now and then it cuts out and won't come back on unless the truck is off for a few hours.

Here is what I've noticed:

1) Won't work at all if temp outside is 97+, even from the start (we are getting slightly above a hundred here in East Oregon)
2) Won't work in 90+ if I let the truck idle with the A/C on for 5-10 minutes, or if I turn the truck off, then back on in 5+ minutes. As long as I keep driving, I haven't had a problem.
3) After it quits, it won't begin to work until it sits in the shade for a long time (many hours).

The evaporator fins aren't plugged, they look fairly clean. I believe that there isn't an evaporator temperature switch to replace.

What else should I look for? What do I need to know about the system above the basic Evaporator/Condenser knowledge? The A/C works every morning, so I can't believe that the issue is mechanical, like the clutch not engaging (except for maybe a plugged evaporator).

Any help is appreciated!

 

When you recharged it did you weigh the gas back in or did you just use a can, if it wasn't weighed backing you may have to much gas in the system and if you used the cans that also has oil in it you may have to much oil in the system. I'm thinking you have to much gas causing high head pressure.

Denny

 

Believe it, go check the clutch gap. See HVAC FAQs, link is in signature.

 

Before you do anything, find the high-pressure cutoff switch, and when it's not working, disconnect the connector, and jump the connector with a piece of wire - BUT NOT FOR LONG - the high-pressure cutoff is there for a reason.

If the clutch engages, you have too much refrigerant in the system causing the pressure to get too high. Check the pressures with a set of gauges and make sure the high-end doesn't go too far.

If the clutch does NOT engage, check the air gap. When things get really hot, everything expands, and the air gap will be every-so-slightly too big to engage the clutch. Not to mention the winding resistance in the electro-magnetic clutch goes up so it's weaker. Cool everything down, it starts to work.

Also, when you check the high-pressure cutoff, if jumping it doesn't do anything, try jumping the LOW pressure cutoff. If the clutch then works, you might not have ENOUGH refrigerant. (I'm trying to remember if too much can cause low-pressure as the fixed orifice doesn't allow enough past, but I forget). The low-pressure cutoff switch can also be intermittent and heat is causing it to fail.

 

You can also have a plugged or restricted office causing low suction pressure and high head pressure. The only way to really check anything you have to have a gauge on the high and low side otherwise you can destroy the compressor by over charging that's why I hate to see anyone use the charge kits that use the low side only. To much gas or not enough gas can also cause excess oil to migrate into the system from the compressor causing the orifice to look restricted. Then if to much oil is out in the system and comes back to the compressor faster than it can separate it so then the system oil will end up in the compressor and oil will not compress so guess what happens then. There's always a reason why the system looks or is low on gas and just adding it will not fix the problem but can cause more problems.

Denny

 

A lot to respond too. I appreciate the feedback:

RVPuller - I used the gauge that comes on the recharge kit, at 65 degrees ambient this morning there was 70 PSI, the gague calls for 30 PSI, so I drained down the 40 to see what would happen, on my short trip this morning I could hardly tell if the air was colder or not. What is the correct PSI? Or is that the wrong measurement? Does PSI on the high and low side at ambient temperature reveal the correct amount of coolant?

Project - I'll check on the gap tomorrow. Thanks for the link.

Krewat - I like the jumping trick, I'll try to get to that tomorrow also.

RVPuller - I had the thought on the orifice also, but didn't think of dual gauges as a way to check.

 

Oh, I just read the FAQ's, I should not have released the coolant. Am I supposed to be checking the pressure while the vehicle is running?

Gonna have to watch some You-Tube videos...

 

Always check the pressure when it's running, and try to make sure the clutch is really engaged when you do it.

Otherwise, the ONLY way to check an AC system is with dual gauges. Without both, there's no way to tell what's going on.

Denny, you make a great point about the plugged orifice. I've never come across one, most of the stuff I used to do with AC didn't have fixed orifices (which tells you, I haven't played with any AC stuff on vehicles from the last 20+ (30+?) years. In my case, all my vehicles continue to operate well with the factory charge, even my almost-20-year-old Cougar is still going strong).

Heck, even a clogged accumulator/dryer can cause high pressure.

But we (I) am over-analyzing. Check the system with dual gauges, and if the high-side and low-side are within specs, and the compressor is still shutting off and not running, start checking the low/hi pressure cutoffs. Then, check the air-gap to make sure the clutch is working correctly. (personally, I'd hook up a volt meter to the clutch feed to make sure the clutch is engaging when voltage is applied).

Now, one thing to mention, before I get piled on - since you already added and removed coolant, the only way to make this right again is with gauges to check what's going on. It very well may be the air-gap all this time, but now you've messed with the base-line

 

Getting a reading at any one time one a automotive system is hard because of the varying speed of the compressor. The only true way anymore is to recover the gas with as recovery machine and weigh the charge back in. When the gas is all out of the system is when you check the orifice.

If you were short of gas you have a leak that needs to be fixed, if you have high head pressure you have a restriction that needs to be fixed. Now one more thing if you have a leak on the low side you may have only lost one element of the 135A gas because it's a blend and after it expands the different elements of the gas don't have the same size of molecules so you may have lost just one part of the blend and that will cause high head pressure. That's also why 134A or any blend gas has to be charged as a liquid not a vapor. But without a set of gauges that read both high and low pressure it's just a guess.

Denny

 

Alright, I found a guy with gauges and a vacuum pump. We evacuated my system, and pulled a vacuum on it. after 10 minutes there was an ever-so-slight leak apparent, we stared at the needle for a while to see if we could verify the leak. He felt that the leak wasn't big enough to be afraid to charge the system back up, so we put in 2 lb 8 oz per specs.

We couldn't get the compressor to start but verified that the truck was calling for it to function. While I was tinkering with it a bit more I learned that if I have the truck off, but the key on, I can turn the clutch head and get it to engage, then when I start the truck, I have AC.

I can't get the clutch to engage without doing it by hand, but I can get AC by following the procedure every time. Do the electromagnets get weak with time? Is this just a gap issue?

Thanks again.

 

Good grief, I told you a week ago to check the clutch gap. You mean you've been screwing around all this time and still haven't done that????

 

I haven't been screwing around with it. I was busy at work this week and elected to deal with the heat until I could mess with the truck today.

Unfortunately, where I live nobody has the special AC Clutch tightening tool. I'll have to wait until somebody heads into town to see if I can rent it from an auto parts store or shop.

There's not a way to tighten the clutch without the tool, is there?

 

By the way, Denny, I love the trivia. Thanks for the info.

 

If it keeps its charge the raise in the gauge is from residual gas that is coming out of the oil. You would have to keep a vacuum pump on it for a long time to get it all out.

Denny

 

No problem but it's what I did for a living but not automotive except my own and as few friends, I worked on compressors as big as some car motors but they basically all work the same, refrigerant going from a liquid to a vapor adsorbing heat when it expands.

Denny