I'm beating my head against the wall here... (yeah, I know it's not a Ford; bear with me here... )

This thing eats a random AC component every year. Usually a compressor or dryer, or both. This comes from the extreme duty cycle, and America's decaying infrastructure.

Standard procedure for dealing with this is to replace the damaged component, and then dump in 3 cans of 134a and I'm back in business. No, no vacuum down, no flush, etc; I don't have the shop to do it myself, and not enough ready cash to have a truckstop do it, and usually not enough time.

3 cans is enough to at least get some semblance of cool. That's 36 ounces in a system that calls for 54 ounces.

But this time around, it's not playing right. The dryer exploded, and trying to hammer refrigerant against a solid wall took out the compressor. I replaced the compressor and the dryer last month (2 weeks of vacation invervening). The remaining dessicant granules in the system clogged the high-side line to the bunk evaporator, and I finally managed to get them blown out. I put the system back together, and I start adding cans of 134a.

It's been 105+ the last three days.

Wow, only one can has me at 45 on the low side, and nearly 200 on the high side. It's never this high on only one can. Three cans has me up to 60 on the low, and 300-ish on the high. The vents are WARM.

My gauge-based troubleshooting guide says that's an indication of excessive air and/or moisture in the system.

O.k... So off to Harbor Freight to get a pneumatic vacuum pump. Hook it up, and get the system pulled down to about 25-inHg. Start adding refrigerant. SAME PROBLEM. Pressures are too high. Even taking into account the pavement-melting ambient temps.

What am I missing? Pressure Minutae aside, what step am I forgetting? Am I not using the vacuum pump right (a possibility)?

-blaine

 

You're missing the common problem of debris in the condenser which is blocking flow. You'll have to replace it along with the standard stuff that gets replaced (orifice tube, dryer, o-rings, etc). You might also need to replace the line from the compressor to the condenser if it has a muffler on it.

 

Hmmm.... :-/

I was REALLY hoping to avoid that, if at all possible...

Today seems a little better... I haven't checked the pressures yet, but the temps are more in line with "historical norms"....

There's so much "thermal mass" in here that it often takes HOURS for the temps to return to something liveable, if the truck has been in an afternoon heat soak condition.

-blaine

 

By taking so many shortcuts and doing partial repairs to "save" money, you have now cost yourself a whole bunch more than if you had done the repair correctly the first time. You have "cheaped" the whole system totally to death!
The main reason you were blowing up compressors in the first place is because you're not removing the non-condensable air and moisture from the system by pulling a vacuum. This causes the head pressure to go very high and overstress the compressor.
You also have repeated failures which have filled the condenser and other downstream components with debris. The next weakest link is the receiver/dryer between the compressor and the restricted condenser. The refrigerant has no place to go and...boom!


You are now looking at:
-New condenser (big $$$ if it is also the grille of the truck like many I've seen) There's no saving or flushing it at this point.
-New compressor.
-New receiver/dryer.
-New expansion devices (x2 if it's a dual cab/bunk system)
-Full solvent flush of the remaining lines, evaporators and any other related components.
- As stated, if any of the lines have mufflers (metal cans) in them, they will also need to be replaced. Mufflers cannot be flushed.

At this point you have 4 options:
1. Find the money to have it fixed right. (~$3-4K wouldn't surprise me.)
2. Find the money and time to fix it right yourself. (~$2K as a guess)
3. Roll down the windows and live without the AC. (Consequences of your actions)
4. Sell the truck and buy one with working AC, then fix it right the first time when/if it breaks. (I'm not suggesting this as a good option, but it IS an option).

 

Replaced the condenser. Pulled a vacuum. Filled it with as close to 55oz of 134a as I could manage.

Nice and cold now. That's all I needed.

For the record, in MY accounting methods, spending all the money to do it "the right way" gets thrown away when the components are simply beaten to death from the incessant pounding. I put as many miles in a year, as most people put on in their car's entire lifetime.

In any case, thanks for the nudge necessary to get the new condenser.

-blaine