97 F150 4.6. New AC compressor, accumulator, hi pressure switch by radiator, fan clutch, condenser, lines. Cools down to 34.5 on a 106 degree day in N. Ft Worth but at idle hi side pressures climb to 280/300 then the pop off valve on compressor dumps refrigerant. If I shut ac off quickly I can easily recharge. May be a bad valve but I think the compressor needs to be replaced to replace the valve.

Any ideas?

 

If the pressures are high enough to pop the valve it's overcharged. It needs to be vacuumed then an exact measured amount of refrigerant needs to be added.

 

If the valve blows off at "only" 280-300 psi, the valve is defective. It is individually replaceable but, of course, requires the system to be evacuated first.

That doesn't explain why the pressure is that high though. Most likely, there is insufficient heat being rejected by the condenser.

 

If there is a blockage in the high pressure line somewhere that could also cause high pressures. With all the stuff you replaced, I'm sure you also replaced the orifice tube?

 

If it pops only at idle but works well at road speeds (hard to tell from the vague description) it's an issue related the condenser as I described. A clogged orifice, for example, would cause issues at any engine or road speed.

 

Yes, the line with orifice tube was replaced -twice actually, 1st at initial installation then again by a shop in Ft. Worth.

 

I would presume an AC shop could find a new pop off valve & will have them search.

As far as the heat dissipation, is it necessary for an electric fan setup. I would think factory should be sufficient.

thanks

 

If the fan clutch is not locking up when needed, that would be insufficient.

 

You need to weigh in the correct amount of refrigerant. Evacuate the system and pull a strong vacuum on it for 5-10 minutes at 29 inches or so.
Many things can cause the high side pressure to rise, most often in residential AC's is a dirty evaporator coil. Clean yours, it sits right in front of the radiator. Make sure the air passages on the radiator are clear also and make sure the fan is running the way it's supposed to.
Air or other contaminants in the system will also cause the pressure to spike *unless* the orifice tube stops up; that'll show up as low pressure on both sides.
On AC, the three important things are clean coils, clean refrigerant system, and weighing in the exact charge. Clean the coils!
Did I mention cleaning the coils?

 

Thanks for all the replies. I guess the next steps will have my ac shop 1-replace the compressor pop off valve. 2. check the orifice/condenser for obstructions-it is a new condenser and orifice tube & lines but may as well check it again while the system is down. 3. vacuum & recharge the system.

As far as cleaning the coils, the condenser is about 3 yrs old but has fewer than 2,000 miles. Is there an easy way to clean the evaporator coils inside the truck, without complete removal of the dash?

 

Have you verified the fan is working like it should? Maybe check the temp on the inlet and outlet of the condenser?

 

I haven't figured out how to access the evaporator easily. The good news is those stay cleaner a lot longer than the condensers do.

 

Since you replaced the fan clutch you should be getting enough air through the radiator and condenser...Now if the back of the condenser is filthy that could raise your high side pressure at idle...Or a weak high pressure valve in the compressor...
At 106 F your high side pressures will be 245-290 psi and running well...I am in Austin and my 03 runs 37-45 F with the temps over 100F and my high side is actually over 300 psi a couple of days ago...
2 questions??? Is the a/c compressor reman or new Motorcraft and was the system flushed especially the condenser if there was a lot of debris on the orifice tube when you pulled it? The high side pressures should be 2.3-2.7x ambient temp at the condenser so 300 psi is not too high in the system but lack of airflow through a dirty condenser will cause high side pressures to spike higher... If there was a lot of aluminum or particulate on the orifice tube your condenser might need to be replaced as some debris can't be removed through flushing...Do you have a pic of the orifice tube? And is your new compressor a reman unit? Sometimes the high pressure valve is not as strong as it should be...

 

I miss the old R-12 systems with a sight glass. I had a 1970 Pontiac Grand Prix with the old rotary GM compressor that ran constantly. Charge till the bubbles go away, check pressures, low side 30, high side 150 to 180, and it would freeze you out, 38 to 42 degrees F at the dash.