Automotive Air Conditioning Information Forum

Microtube parallel flow is going to cool the best for a given condenser dimension. A subcooling model would work even better but it is hard enough to find a proper dimension microtube parallel flow for older vehicles as it is.

Your pressures sound like what my Express van did when the flat out wrong rear expansion valve was cross referenced and installed. Turns out the replacement valve had a 28K BTU rating where a 12K BTU rating valve was. I would suggest an OE valve if possible. Mine has an aftermarket unit and was equipped with a Parker valve that has been long discontiued. I did find a solution on mine though. It had an R12 style SAE fitting equipped valve and the ac catalogs cross referenced it to the much higher capacity Four Seasons China made valve. I ended up swapping to a USA made valve from Old Air Products that they use on their similarly sized BTU wise Hurricane unit. The low side pressure dropped from 50-60 psi to 40 PSI and the high side increased from 225-230 to 275 psi when the valve was no long just dumping refrigerant through it. Might not be your issue but worth checking into. The rear expansion valve thermal bulb should also be clipped to the suction line inside of the rear hvac case and wrapped in thermal protection tape so that it can accurately measure the evaporator superheat temperature. Mine had ice cold rear air and the suction line was actually frosting all the way back to the compressor before correcting the expansion valve issue. The rear expansion valve was in effect robbing refrigerant flow from the front fixed orifice tube setup as well as raising the low side pressure increasing the temperature of the refrigerant boiling in the evaporators.

Your pressures tell me you either have a weak compressor perhaps the wrong size pulley on it or too much flow area in your refrigerant metering. The front is fixed orifice leaving the expansion valve to question. If the pressures do not change when you shutdown the rear blower that would also push me further toward a rear expansion valve issue.

I just dug into the Ford catalog. Looks like the OE rear expansion valve is an H block. Ignore what I said about the capilary as it does not apply. That being said if it is not an OE expansion valve, get one and try it first before you spend days chasing this ac cooling ghost. The pressures definitely look like I would expect with an expansion valve hanging open. To cool properly your low side pressure needs to get under 40 psi at 2,000 rpm and should in stock condition. With the rear unit shut off I would expect to see 30-35 psi on the low side at 2,000 rpm as a maximum even in 100F.

So let's rule out a weak compressor.....
Recommended testing process for this vehicle?

Without rehashing all the reasons to suspect the rear TXV, I agree with Carguychris85 on this one. Suggest purchasing an OE TXV, install it, recharge to specs, and then test the system's performance.

JohnHere wrote: ↑Sun Jul 28, 2024 7:02 pm Without rehashing all the reasons to suspect the rear TXV, I agree with Carguychris85 on this one. Suggest purchasing an OE TXV, install it, recharge to specs, and then test the system's performance.

OE TXV will be here on tomorrow morning's Ford run.
I really need to max out the compressor and make sure it's still strong, I had metal flakes on the Orifice tube when I swapped a standard one in for the variable one in use at the time.
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It was not a flushing issue, as lines were flushed 4 times, twice in each direction and every other component was brand new

Carguychris85 wrote: ↑Sun Jul 21, 2024 6:55 pm To cool properly your low side pressure needs to get under 40 psi at 2,000 rpm and should in stock condition. With the rear unit shut off I would expect to see 30-35 psi on the low side at 2,000 rpm as a maximum even in 100F.

Thanks
Pressures are wonky for sure, have a OEM TXV valve headed to the shop on the morning run. I'll confirm compressor is not weak, then evac and install the OE TXV, recharge 10% under by machine, then hook up manifold gauges and a can of 134R to finish charge by pressure.

Erik In TX wrote: ↑Mon Jul 29, 2024 5:35 pm OE TXV will be here on tomorrow morning's Ford run.
I really need to max out the compressor and make sure it's still strong, I had metal flakes on the Orifice tube when I swapped a standard one in for the variable one in use at the time.
It was not a flushing issue, as lines were flushed 4 times, twice in each direction and every other component was brand new

Forgot about the new compressor. Might have been some metallic debris left over from the manufacturing process. Hopefully, it was, and all is well.

Might as well pull out the OT while you have the system open for TXV replacement and see what it looks like now.

JohnHere wrote: ↑Tue Jul 30, 2024 9:36 am

Erik In TX wrote: ↑Mon Jul 29, 2024 5:35 pm OE TXV will be here on tomorrow morning's Ford run.
I really need to max out the compressor and make sure it's still strong, I had metal flakes on the Orifice tube when I swapped a standard one in for the variable one in use at the time.
It was not a flushing issue, as lines were flushed 4 times, twice in each direction and every other component was brand new

Forgot about the new compressor. Might have been some metallic debris left over from the manufacturing process. Hopefully, it was, and all is well.

Might as well pull out the OT while you have the system open for TXV replacement and see what it looks like now.

Thanks ya did that today...few flakes of aluminum. Not likely left from the previous system as it was all replaced, not just flushed.
New OEM expansion valve installed, new orifice tube, new filter in rear line, evac'ed to 29.8 for 60 min, charged to 68 oz per spec....
LP 55.5, HP 255 on a 95 deg ambient temp day best I can get on vent temps today is 57 deg.
LP/HP to me indicates a dying compressor.
Checked condenser and have consistent heat decreasing heat across laterally and even top to bottom. So I have flow, IOW not plugged.
I disconnected the fan clutch and blocked the condenser....... 290 psi was highest HP I could get

Again makes me think weak compressor.

Another tidbit.... we have evac'ed and recharged several trucks with an as originally equipped component AC system as part of lifting cabs....Vacuumed down for just 30 minutes, charged to OEM spec, no dryer replacement, no orifice tube replacement....... pressures and vent temps exactly as they should be no drama...... This leads me to believe this is not a technical, process or refrigerant issue, but a parts issue with mine and others we have used non-OE replacement parts on. (No choice, OE parts no longer available)

This is a long thread and getting hard to follow.
Has reheating been eliminated? Those pressures are too high. Clamp off the heater hose.
Are there under hood components too close to exhaust components, if so insulate them. Is the low side line insulated?

tbirdtbird wrote: ↑Mon Aug 05, 2024 6:19 am This is a long thread and getting hard to follow.
Has reheating been eliminated? Those pressures are too high. Clamp off the heater hose.
Are there under hood components too close to exhaust components, if so insulate them. Is the low side line insulated?

Dual evaporator system is going to run ~50-75 psi higher on the high side and 10-15 psi higher on the low side than a single evaporator system. I would not trust the pressures at idle, habe to check them at 1,500-2,000 rpm.