I had a friend put his AC gauges on the 93 CTD because the air was blowing cool but not cold. We added 12 oz of freon to system but afterwards the high pressure side is reading 350 psi once the rpm's are brought up over idle. After looking at service manual I beleive this pressure is probably to high, should be around 240 psi. Some of the probable causes stated are worn clutch fan and H valve sticking, although the clutch fan seems to be moving plenty of air to me, did notice that it spins 6-8 revolutions after truck is cut off. How can I check the clutch fan? Is 350 psi to high for system pressure and what could happen? the book also states that there is a high pressure relief valve in line that vents around 450 psi. Need to get this taken care of ASAP, have a trip planned to DESTIN FLA in a couple of weeks with my slide in and boat in tow.
thanks in advance

 

Is the engine overheating? If not it probably not the fan drive. With the engine off(obviously) grab the fan and spin it by hand, it should stop almost immediately, if not the viscous fluid is failing and the drive needs replacing. To test the thermostatic spring the FSM says to lift the end of the thermoststic spring out of the slot in the fan drive. Then rotate spring counterclockwise until the stop is felt. The gap between the end of the coil and retaining clip should be approx. 12mm. Replace unit if shaft doesn't rotate with coil. Good luck, AC problems can really suck sometimes.

 

The truck is running normal temp and the fan stops quickly when spinning by hand, although it does spin a little easier when hot verses cold. I'm wondering if 350 psi on the A/C high pressure side is enough to bust a hose?

 

If the hoses are original(old) it might be possible, but hopefully the high pressure relief valve does it's job first. Before you added the freon(still r12 in yours?) what was the sight glass in the R/D looking like?

 

The sight glass had bubbles in it. I added Freeze 12, which is a replacement sold for R-12 systems at NAPA. The hoses are original along with everything else in the system. I may just run it and see what happens, just really didn't want to be on a long road trip when it decides to let loose.

 

I know nothing about freeze 12 specifically but the freon replacements like Duracool say the r12 has to be evacuated completely before adding anything but r12. Did you mix the freeze12 with regular r12? Edit: Just found a web site for freeze 12 and it says it works with r12, so skip that question. Did you add any oil when you did the freeze12? If not I'm wondering if the system has too much refrigerant and or not enough oil to move the refrig.

 

The total capacity is about 44 oz when using R12 according to a retrofit manual I have and the high side pressure around 250. They say 1300 rpms while checking pressure in the factory manual.

From retrofit manual "The higher the high side pressure the harder the compressor must work. This higher pressure also has an effect on the refrigerant entering the low side and it's ability to pickup (absorb) heat subsequently affecting the duct outler temperature"

I'm currently getting all the parts and info together on a 134a retrofit for my 91 CTD.
It will include the addition of a high pressure cutoff switch while retaining the stock low pressure cutoff switch. I have most of the parts sitting here and i'm changing everything except for the compressor and evaporater. Waiting on a switch and the PAG oil. I'll write something up on it when I do the install/conversion.

Den

 

freeze 12 is a drop in replacement for r12 theres no need for evacuating the system, mr jimmy thats to high under normal conditions , but the high side will be unusually high in certain conditions but will come down,, if , it was very hot outside and or very hot inside.

The highside presure under normal circumstance is controlled by three factors the air flow over the condenser and ambient air temp,if it was very hot the pressure will drop as the interior of the truck cools , also simple over charge can cause a jump in pressure , but that seemed a bit high unless it was 105 outside, the fact there was bubbles doesnt mean much with freeze 12 it takes less of it than r 12, if you could supply the outside air temp and both low and high pressures i can help you a bit more.

Note 134 doesnt perform as well as R12, if you can find it freeze 12 is a better choice, it can be purchaced without an EPA certification ,and theres no need for a retofit,i give 5 bucks a can for it at a local auto store.

 

i would recomend ester oil over pag oil, if for no other reason i have 4 mopars with 134 installed 2 of them over 3 summers. 2 of them with v type compressors. was told it would not work well in the v-type. one was actually 4 degrees colder than 12 under same conditions.

 

I just changed my fan clutch, BIG differance! The instructions said that if fan turns more than 1 1/2 times after shutting off with engine at operating temp.... fan is bad...Truck now never goes past 1st mark on guage and the AC works WAY BETTER even while setting in traffic!!

 

Turned out to be the expansion valve. All is well now!