New R12 AC system in Dodge D150 blowing relief valve - lack of condenser airflow?

[james89dx]

I just installed an entirely 100% new system in my 89 Ram D150 318. Every single component brand new. I stayed R12 and added exact amount of R12 by weight with my refrigerant scale. Added 44 ounces total.

It has a brand new fan clutch and condenser and the shroud which fits around condenser and radiator is in place and undamaged.

Almost immediately upon getting the full charge in, the relief valve built into that “muffler” on the high side discharge line right off the compressor blew and sprayed a bunch of mineral oil and refrigerant out for a few seconds.

I noticed at idle that the compressor never cycles off although I did not have the idle speed pinned at 1300 as mentioned in the manual - I just left it at base idle. I took the truck for a drive and the vent temps were pretty subpar - we’re talking low 60’s at center vent (and it was about 90 degrees last night in Dallas and about 45% humidity). If I wanted subpar vent temps I’d have gone R134 lol.

Got it back home and put the gauges on it in the driveway and I see the high side pressure gets up above 400 fairly quickly and after a couple of minutes it blew the relief valve on me a second time. I got out the water hose and with the hose steadily soaking the condenser it nearly instantly brings the high side pressure down and after only a couple of minutes with the hose I get mid 40 degree center vent temps - perfect! However, I do notice that the compressor never cycles at idle - but again I did not adjust the idle speed to 1300 or whatever is called for in the manual and again manual states this is normal around this current ambient temp.

So my questions are -

1. How can the OE fan setup be so woefully inadequate?? This is so surprising to me. Is this a common issue with AC systems in these trucks?

2. What exact conditions should cause the cycling switch to cycle? The manual mentions a range of temperatures (68 to 90 degrees) in which it should cycle and does also mention that above 90 degrees it may not cycle at all which is normal. Given that, and that I was right there around 90 degrees ambient temp... perhaps the fact mine never cycled is normal. It doesn't however list the actual pressures which is what I'd be curious to see.

3. Is there any reason I shouldn’t just add a couple of slim high power electric fans on the front of the condenser run off a relay activated by the compressor turn on wire?

4. What should I do about my lost oil? I am well aware that refrigerant oil always “looks” like more than it is when you see it puddled or spray out but I’d guess it might be at least 1/4 oz lost. Is it worth it even trying to bother to add some back? I started out with a bit over 7.25 oz total system volume. I have one of those dye injection syringe deals I could probably add a bit back.

Thanks for any help/tips. Really looking forward to some good AC in this bad boy finally.

[bohica2xo]

Mopar has a long history of fan speed ratio changes with the LA engine. Any mopar forum is full of folks that are clueless about when, why & how it works.


Non A/C 318's started with cooling fans running at pretty much 1:1 with the crankshaft. A/C cars had a 1.5:1 OVERDRIVE on the water pump & fan. One of the reasons they have so many belts & belt choices. After 50 years of production parts being swapped around on older cars you are likely to find anything for a drive ratio. I have a stack of LA crankshaft pulleys on my shelf from a little over 6 inches to over 9 inches OD, some with 3 different diameters all at the same time & 4 belt grooves total. Water pump pulleys from 5 to 7.5 inches too.


So you had a non-A/C vehicle. It may have had an 18" fan, while the A/C vehicle has a 19.5" fan. It may have a small crankshaft pulley. Many econo-box trucks had reduced accessory speed then, trying to produce better fuel mileage on the CAFE dyno.


The good news is Dodge was an early adopter of higher efficiency condensers. Yours should be a Piccolo type. It just needs enough airflow. Since you are in a very high heat load area I would not expect the compressor to cycle off.


Please measure the fan diameter, and the drive pulley diameters for us. Take a look at the fan tip to shroud clearance, and how deep the fan sits in the shroud as well.


B