Automotive Air Conditioning Information Forum

Hi there,

Just joined the forum

I recently changed the variable displacement compressor in my Ram 1500 to a fixed displacement compressor, the original was 7sbh17c denso that I have replaced with 10sre18c valeo. The valeo unit I believe is the same as the oem ones for the 2009-2010 year for the same truck. I took out the control valve of the original compressor and connected the plug ( so that the hvac module can't tell I changed the type of compressor and keeps everything runnig ) and zip tied it to the frame under the hood.

I did this to get better cooling since the original hvac system keeps changing the temperature according to multiple sensors readings and would never let the ac vent temp get below 48°, well, I live in Saudi Arabia and this kind of temperature would never get the interior cool enough, specially with the ambient temperature getting over 120° frequently.

Well, after replacing the compressor and charging the system with the specified weight on the hood sticker(510g) the temps were worst than before(idle and freeway), after this misfortune, I kept venting (sorry environment no recovery machines here ) the refrigerant untill I got the system to 30 psi at idle at 95° ambient. This is the best performance I could get up until now. At freeway I could get it to blow a nice 40° out the vent. I'll try to find a shop with a recovery machine to get the exact weight of refrigerant I have in the system now.

I should mention that I also converted the system to 134a instead of 1234yf.


So after this long introduction, how should I know the exact weight of the charge considering that I changed compressor type? Also, the idle vent temperatures are always above 50° both with full charge and vented charge, with vented being slightly colder. How could I get better cooling at idle? PS, I got SPAL pusher fan waiting to be installed soon.

Just wanted to add another question, will running my ac system while undercharged hurt anything?

When I put the full charge of refrigerant as per the hood sticker, the pressures at idle were 40-42 low and about 200 high (need to verify that again), but when undercharged low side reads 30 low 180 high on a 88° day.

I took a screenshot of the alfaobd app monitoring the hvac module
I wrote the temps in F° and the pressures in psi since my phone shows metric readings and Arabic numerals.

Those readings were taken at night not even when the sun is up.

I am no help on your situation, I am just amazed at the info you can get from the RAM with that app. That's a cool app.

Fus88 wrote: ↑Sun Aug 27, 2023 12:05 am I took a screenshot of the alfaobd app monitoring the hvac module

andrew vanis wrote: ↑Sun Aug 27, 2023 4:24 pm I am no help on your situation, I am just amazed at the info you can get from the RAM with that app. That's a cool app.

Fus88 wrote: ↑Sun Aug 27, 2023 12:05 am I took a screenshot of the alfaobd app monitoring the hvac module

Yeah, the technology we have today is great, scary and frustrating sometimes. I'm in a love-hate relationship with it - specially when it controls my hvac -.

OP, converting a system from R-1234yf to R-134a is illegal in the USA and violates US-EPA regulations. Therefore, I don't think you'll find anyone on this Forum who will offer advice about such a conversion beyond what I've already said.

JohnHere wrote: ↑Mon Aug 28, 2023 6:22 am OP, converting a system from R-1234yf to R-134a is illegal in the USA and violates US-EPA regulations. Therefore, I don't think you'll find anyone on this Forum who will offer advice about such a conversion beyond what I've already said.

Well, I live in Saudi Arabia and it is legally allowed here as far as I know.

Also, in case that I went back to 1234yf, same questions posted above but with the original refrigerant.

So, after some fiddling around I believe that I had a bad txv that I replaced previously when my evaporator went bad, after replacing the original txv and charging the system with appropriate amount, ac blows 43°-49° in 110°+ ambient.

Just an update in case someone had the same issue I had.

Thanks for the update.....So the replacement TXV was bad and you put in the original and all worked well?

andrew vanis wrote: ↑Tue Sep 05, 2023 6:16 am Thanks for the update.....So the replacement TXV was bad and you put in the original and all worked well?

Yes, that seems to solve the problem of bad cooling at idle.

On the highway or when driving in general, the evaporator now get down to freezing temperature and the clutch disengages for a few seconds then clicks in again.

In general, I'm quite happy with the performance of the ac for now.