Automotive Air Conditioning Information Forum

Here is a page from the Evans Tempcon RV manual for Front Occupants HVAC Service Manual. Pressures are listed as PSIG???

Regarding charge amount - the only 2 numbers I have come across are 2.13 lbs (34 ozs) from the same Evans Tempcon manual referenced in my previous post and 2.5 lbs from the Ford Chassis manual for 2015 F53. I put between 34 and 36 ozs in when I recharged.

Your latest test @1800 rpm showed 14psi low and 210 high side. 95f ambient, and a vent of 60f With 40% humidity

So if we look at the chart provided by Evans

At 90f intake the average temperature drop across the evaporator is 30f . You are getting 35f right now

At 90f ambient the low and high side pressures are in line with the results you got. A little low.

I agree with Tim, a little undercharged at this point. It is already meeting the OEM temperature drop. It is 1psi low on the low side.

FYI the term PSIG simply means PSI Gauge. As opposed to PSIA - which would be absolute pressure which includes atmospheric pressure.

bohica2xo wrote: ↑Fri Jun 07, 2024 10:20 pm I agree with Tim, a little undercharged at this point. It is already meeting the OEM temperature drop. It is 1psi low on the low side.

I don't think by much. If you have access to the inlet and outlet pipes on the evap. They should be the same temperature.

Thank you both! I guess I was reading the chart right but 55-60F vent temps doesn't seem that good (probably exacerbated by the fact that this is a motorhome)!

I will add 2-4 ozs and leave it at that - that should get me right at the 40 ozs indicated in the Ford F53 chassis manual.

I'll take a look at the evap temps tomorrow.

55f discharge air with 90f ambient is pumping heat away. Once the cabin temp drops 10 degrees, so does the evaporator inlet temperature...

bohica2xo wrote: ↑Fri Jun 07, 2024 2:14 pm John: I can answer part of that question for you. The F53 in that model year has the 6.8L V10 engine mounted conventionally with a viscous drive fan clutch. Truck chassis.
The fan is 19.6" diameter with 8 huge blades. When the clutch is working I can hear one for blocks. That kind of torque load can be hard on a clutch.

Thanks for that information. Since this is a 2015 model-year motorhome, the fan clutch might be worn out.

rgnprof wrote: ↑Fri Jun 07, 2024 4:18 pm Yes, I see the big 8 blade fan behind the radiator and yes, this is the 6.8L Triton V10. I have no electric fans.
Just checked pressures at 1800-2000 rpm - hi side 210 psi and lo side 14 psi. Maintained that for at least 90 seconds and didn't change much. At idle, high side 215 psi and lo side 27 psi. Temps in front of the condenser about 95F (humidity today about 40%) and vent temps at 60F.

Your HS pressures look good, so it's up to you whether to replace the fan clutch.

I wouldn't be satisfied with a vent temperature like that, which won't cool the large cabin of your motorhome much at all. Given the LS pressures you posted, the evaporator has to be ice cold, so 60°F vent air doesn't make sense to me unless the evaporator is just too small for the heat load.

Are you sure something else isn't going on, like heated air mixing in with the cooled air?

John,

Funny you should bring up the possibility of heat mixing with the AC...it appears that this is not an uncommon problem with these motorhomes. The water valve is electric, but I'm not sure how to test it. Someone mentioned trying to clamp it off to see if the vent temps get colder. I tried but I'm not sure if I did it right.

The diagram attached below is a typical Ford/Evans setup - the water valve is right in the middle of the diagram.

We had some issues in the mid-2000s with Ford Vans not cooling. The evap was tucked into the engine bay next to the motor, with a Small Evap core and a significant heat load. We lined the Evap case with reflective heat insulation. We had the customer's (work vans) block off behind the driver. Still, we had poor cooling. In Arizona, we never got them to cool sufficiently in our temperatures.

Here is a link to the water valve:

Do not post eBay links on this site. Please read the posting rules.