AC Black Death on 98 5.0 Please Help!!!

[Bruce Rock]

Need some more help, if you guys don't mind. I bought a manifold gauge set from Harbor. With the system off, I'm reading 82 on both sides. With the system running, I reading about 38 on the low and 225 on the high, outside temp is about 90-95. Can't seem to get air colder then 66. Still cutting off on higher RPMs. When I rev the engine to 2500 rmp's the low drops to amost or past 25, at which time it cuts off. If it stays above 25 and doesn't cut off, I'm reading 275 or 285 on the high side. I've replaced both high and low side cutoffs and the WOT relay. Not to mention the return line, condensor, accumulator, and orifice tube. My drive today to Charleston in this heat is going to suck.

One thing I found wierd. The directions say to have both valves open while testing with the system running. Won't this transfer high pressure to low pressure?

The charts didn't copy. If you operate your air as described and than send me the readings I'll check the charts. This information is on the 1993-1994 Ford Truck workshop information CD. If you don't have a copy I suggest you get one. Ebay has them or I'll send you a copy of mine for a $5.00 donation to this site (Serious Exploratons)

I'll have to check the directions for my harbor freight manifold gauge set. I seem to remember reading the same thing and having the same thoughts.


Refrigerant System Tests

The following test conditions must be established to obtain accurate pressure readings:

l Run engine at 1500 rpm for 10 minutes.

l Operate air conditioning system on MAX air conditioning (recirculating air).

l Run heater blower motor (18527) at HI speed.

l Stabilize vehicle interior temperature at 70°F to 80°F (21°C to 27°C).

When attaching a gauge set to the system, the low pressure gauge hose must be connected to the service access gauge port valve on the suction accumulator. The high pressure service access gauge port valve is located in the discharge line near the condenser.

Diagnosis of the refrigerant system must be done by analyzing the high pressure readings to the charts shown to determine if the system pressures are normal. The conditional requirements for the refrigerant systems tests must be satisfied to obtain accurate pressure readings.


Normal Cycling, Refrigerant System Center Register Temperature Range




Normal Cycling, Refrigerant System Pressure Ranges




Normal On, Off and Total Cycling Time-Per-Second




Refrigerant System Pressure and Timing Evaluation Chart




Checking for A/C Leaks

R-134a A/C System: Attach the Rotunda R-134a Manifold Gauge Set 176-R032A. Leave both manifold gauge set valves at the maximum clockwise position. Both gauges should show approximately 413-551 kPa 60 to 80 pounds pressure at 24°C (75°F) with the engine not running. If very little or no pressure is indicated, leave the vacuum pump valve closed, open the Refrigerant-12 tank valve, and turn the low pressure (suction) manifold gauge set valve to the counterclockwise position. This opens the system to tank pressure. Check all connections, and the compressor head gaskets, and the shaft seal for leaks, using either the Rotunda Automatic Calibration Halogen Leak Detector 161-R0010 or equivalent.

NOTE:
Use compressed air to blow off excessive oil from the shaft seal area to reduce the possibility of an erroneous detection of freon retained in the refrigerant oil.

 

[Glacier991]

Your pressures are not way out of whack at all - in fact pretty much normal for an operating system with a proper charge. The fact that at 2500 rpm you low presure suction out (eg. your low side switch shuts you down as it should when the low side drops to below 25-27 psi) is suggestive of either a low charge or a plugged or restricted O tube. (I am putting the tube high on the possible culprit list based on your info). In an operating system circulating refrigerant, a low side of 35 psi should be producing air that's pretty darned cold. One other thing - how sure are you of your blend door ?

 

[Bruce Rock]

One other thing - how sure are you of your blend door ?

I don't want to confuse Fiberford but on my '94 there is an H valve.


"H" Water Valve, Explorer

The "H" water valve cuts off the water supply to the heater core when the A/C system is placed in MAX A/C. The valve closes off the water flow to the heater core and allows the coolant to circulate in the hose.

Do '98's also have this valve? If so, and it doesn't leak internally, what effect would his blend door have on cooling? Again, I am basing my question on the air flow in a '94. With an H valve, and the system is Max Air there is no engine coolant going through the heater core so there should be no heating.

FiberFord: I forgot you had a '98. My CD is for a '94. Sorry, can't help you there.

 

[Bruce Rock]

Still cutting off on higher RPMs. When I rev the engine to 2500 rmp's the low drops to amost or past 25, at which time it cuts off.

With an Ambient of 95 degrees F the clutch off time per cycle should be less than 10 seconds at an engine speed of 1500 rpm. This according to the chart for my '94.

 

[Glacier991]

I guess I assumed the A/C was staying off at high RPMs or for extended periods (plugged tube would probably stay off or at least off for some period of time beyond a few seconds - in other words not a cycling thing. A low charge (doubting that's really the problem here) would cycle on and off at some interval, regardless of RPM.