'99 F250 Super Duty- immediate low side drop

[69DropTop]

I don't have pressure readings at 1500rpm yet but can get those tonight or this weekend and report back. I do know it was right around 30 at idle.

[Tim]

I don't have pressure readings at 1500rpm yet but can get those tonight or this weekend and report back. I do know it was right around 30 at idle.

Low and high side readings!

[69DropTop]

I got some low/high side readings. Here were the test conditions: outside air temp 77*, I parked the truck in the sun, opened the doors, set fan on high, set ac on max, had driven truck with a/c on prior to testing, held the engine at about 1500rpm and got 27 on the low side and 190 on the high side.

What do you guys think about those numbers?

[69DropTop]

I posted my pressure readings but didn't get any replies. From the little I know, I don't think the readings are bad but it cools better at idle than when going down the road so that makes me think it could be slightly low still. I put somewhere between 40-42oz of refrigerant in it. I read online that a guy read somewhere that either there was a TSB or someone recommended putting 45oz in it due to improper cooling at highway speeds which is very similar to what I'm experiencing to where it cools better at idle than driving down the road so I was think of adding another 3oz to see what happens. You guys probably think I'm crazy but I want it cool in the low 40s like my Camaro does and a lot of other R134a systems I've seen; I see vent temps of high 40s low 50s anytime I'm driving and that's when outside air temps are in the high 70s or low 80s.

[Tim]

If those pressures are correct. Might check if hot water is getting into the heater core. Also if the inlet and outlet on the Evap are the same.

[69DropTop]

I don't see why the pressure readings wouldn't be accurate. Good point about hot water getting into the heater core. I haven't noticed a hot water shut off valve but haven't looked closely for one either. Do all cars have hot water cut off valves for when the A/C is on? I know my '69 Cougar does but don't know if newer cars still have that. I can check inlet and outlet temps on the evaporator but the outlet seems to freeze and get more frost on it before the inlet does but I will double-check with a temp reading to see what I have.

[bohica2xo]

Heater valves fail.

Also check the evaporator for crud. A plugged up air side will give poor performance, and considerable cooling of the suction line.

A 10 year old pickup truck may have an evaporator full of leaves / dog hair / mouse nests...

[69DropTop]

Heater valves fail.

Also check the evaporator for crud. A plugged up air side will give poor performance, and considerable cooling of the suction line.

A 10 year old pickup truck may have an evaporator full of leaves / dog hair / mouse nests...

At lunch I looked at the heater hoses into and and out of the heater core, no cut off valve whatsover and they appear to be the factory lines. I just replaced the evaporator a few weeks ago so I know it's as clean as a whistle.

[Tim]

Pinch the heater line for a little while. I believe the F50 has a blend door. Were the inlet and outlet the same temp?

[69DropTop]

The liquid line to evaporator was 46 degrees and the evaporator to accumulator was 43 degrees. I took both measurements about an inch from where the lines go into the HVAC box.