Automotive Air Conditioning Information Forum

Hey all! I've been working on my '89 Ford Bronco 2. Obviously it originally had R12, but when I bought it last year at some point someone had changed to R134, due to the R134 connections on the schrader valves. I wasn't sure what had been done, and the AC no longer worked ( though the compressor did short cycle ), So I drained the system, replaced the accumulator, removed and drained the compressor, changed all the orings to hnbr, and attempted to remove and change the orifice tube. I couldn't remove the orifice tube and I damaged the line in the process of trying to remove it. I was able to find a used evaporator ( I know, terrible idea! ) and it also had the same orifice tube ( red ). It looked dirty , but I did my best to remove it, and had the same problem trying to remove it from the line. So I simply cleaned from the outlet side to the inlet side hoping to dislodge any garbage in the tube. Everything seemed to be flowing freely through the evaporator when I cleaned it. Vacuum the system down, it holds vacuum, and charge the system with oil and the correct amount of refrigerant ( 40 ounces of r12 was required originally, I put in approximately 32-34 ounces of r134a ). My pressure readings at idle with an ambient temp of 85 are 30-35 low side and around 250-275 high side. With the engine running at around 1,500 rpms, my low pressure drops from 30 to 22, when the compressor cycles off, and my high side goes up to 325-350.

I'm new at ac theory, but I'm trying to learn, and I'm led to believe there's a restriction somewhere due to those pressure readings, right? The air out the vents is about the same as ambient air temp, and this is the part that confuses me a little, the line directly behind the orifice tube is cold, which is the inlet to the evaporator, but the line coming back out the evaporator is ambient temp. So there's at least some refrigerant making it through the orifice tube, but either not enough to cool the evaporator or the evaporator itself is plugged?

I have several questions and concerns. But first of all, given the pressures you posted, it sounds like a lack of airflow across the condenser. What kind of fan(s) does this truck have and is it (are they) working properly? If the fan has a viscous clutch, how old is it? Does the fan roar noticeably when you start the engine and turn on the A/C at 1,800 RPM? Try misting the condenser with water with the A/C running. What happens to the pressures then?

The fan clutch is original, it is pulling air. I don't believe it's an airflow problem through the condenser, when I drive down the road the air temperature in the vents doesn't get cooler, it starts exactly the same as when I'm sitting still. And like I say, the line just after the orifice tube is cold entering the evaporator, but the exit of the evaporator is warm.

Hard to say what might be wrong internally with that evaporator. The OT problem is common enough that there is a repair kit for it. For now it seems to be working, so let's diagnose the whole system.

Is this dealer installed A/C or factory A/C? Dealer installs were common in those years. Factory air had an FS6 compressor, dealer installed units an SD709 compressor. Other parts were different as well.

Your 1500 rpm high side pressures point to a condensing issue. Poor airflow, check the air path through the condenser.

The low side pressures are not bad, and the warm outlet tells me there is heat being absorbed. Check the air door operation. The one flap has a spring loaded default of defrost with no vacuum applied. A bad vacuum line in all of that underhood spaghetti is all it takes. Is there cold air coming from your defroster?

Need to get the high side pressures under control. An original fan clutch is probably as dead as can be. Try misting some water on the condenser @ 1500 rpm & see where the high side goes.

Looks like several small things all at once.

Encyclopedia 2x0! Heck, I knew that.
hotrodac

I ran it today at 1,500 RPM's while misting water across the condenser with the garden hose, and there were no changes from the previous pressure readings. There is no cold air coming from the defroster, the vent controls work fine in the truck. When I set it to panel, floor, defrost, etc. the air comes out where it's supposed to, it's just ambient temperature.
It is a factory installed AC unit. With High side pressures that rise while low side pressure drops, simultaneously, doesn't that point to a restriction somewhere in the system, not an airflow issue? Like I said earlier, it makes no difference if I'm driving down the road at 55 mph, and I know the condenser ( the fins are clean on it ) is getting plenty of air at that speed.

Right now, the only parts working properly in your system are the compressor and the cycling switch.

The refrigeration system works because of a restriction, in this case the Orifice Tube. Any additional (and unwanted!) restrictions can usually found with a physical inspection - they usually get cold.

My memory is a little foggy on 30 year old fords, but Ford switched over from tube & fin condensers before the 134a change in 1993/4 on some models. I see a replacement condenser for your vehicle that is a Piccolo type condenser. Which type of condenser do you have?

It is quite possible that your evaporator is a mess, given it's history. A new unit is about 60 bucks. Junkyard refrigeration parts are often not worth installing.

Because this is an unknown 134a conversion it is also possible that it has way too much oil in it - many got 3x the oil charge.

It is also possible a previous owner pumped it full of sealer. Some of that stuff lays around in the system - then expands & hardens when it comes in contact with air. The theory was that it would be ejected through a leak & seal it. Opening a system that has sealer in it causes it all to harden.

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One of the questions that came to mind earlier was the orientation of the OT. The long part with the screen should face toward the condenser.

I ordered a new evaporator and orifice tube, installed them yesterday, and started vacuuming the system. I let the pump run for 4 hours yesterday, let it sit overnight without the pump running ( it held vacuum perfectly ), then ran the vacuum pump for another 4 hours today. Charged the system with approximately 32 ounces of 134A, and I'm finally getting cold air out of the vents! Ambient temperature was about 82 degrees F, out the vent temperature at idle was 60* F, at 1,500 RPM's the vent Temperature fell to about 52-55* F. Low side is at 30-35 PSI, High side is at 255 PSI, with the engine running at 1,500 RPM's. The tube going into the evaporator is cold as well as the tube exiting now.
I hear all these people talk about 40* vent temperatures and I have no idea how they're getting that cold! The only car I've ever known to be that cold was my Dad's old '74 Dodge Charger with the original R-12 still in it, and that was in 1999! Every vehicle I've ever replaced orings and accumulator in, and vacuumed down I've only been able to get to around 55* vent temperatures.
My condenser is still the original tube and fin style.

I replaced the entire system in my 88 BII last year. It was my first attempt at doing AC work other than a top off on a charge.
The compressor belt had been off for as long as the previous owner had it, so at least 5 years. I vacuumed it down and charged it to test and the compressor knocked really badly, but it did cool. Figuring I'd rather start with all new I went at it after lots of reading and YouTube vid watching. Something like $800 in parts and $200-300 in tools and refrigerant and pag oil, adapters and insulation. Better than the $2500 the dealer wanted.

So how did it turn out? Best case I got was 38 degrees at the vent. This would be with engine rpm in the 1500- 2200 range while on the road. In the driveways at idle it was something like 20-25 degrees below whatever the air temp was.

In the driveway I got pressures pretty similar to what you are getting. When I say I replaced the entire system, I mean it: comp, condenser, evaporator, lines, OT, fan clutch and fan. If left sitting in the sun there are just too many windows on the BII for the AC to overcome. If the cabin temp is well over 100 degrees, it has be driven to cool it down.

Sealing the condenser/radiator to the core support with foam tape to be sure all air goes through the condenser/radiator, some reflective heat shielding for the evap box and and covering the cold lines with foam brought the temps down about 3-4 degrees at the vents.

My thoughts on making it better; An electric fan would really help when the truck isn't moving. The red Orifice tube may too be restrictive and I'll always wonder if I should have stayed with the stock OT (blue?) even if was for R-12 instead of R-134. I think to get it much better is going to take better sun blocking like a good modern window film and insulating the body as there is just no insulation in the BII that I have beyond the plastic panels and carpeting.