A/C works about half the time

[merc80]

My wife's '95 ex is having trouble with the a/c. It works normally for a while, sometimes over an hour. For example, last weekend she drove to Nashville to run some errands. The a/c worked fine on the ninety minute drove there. It worked during several short trips around town to different stores. On the way home it worked for about 10 minutes, then shut off until she was a couple miles from home, when it came back on again.

I checked the low side pressure the next day. It was about 25psi. One can of r134a later, it was about 45 psi. Ambient temp about 95F through all of this. After adding the r134, it was blowing a lot colder but she says it shut off again about half way home from work. I checked both high and low side pressures this time, low side still about 45psi, high side was about 300psi. According to the instructions that came with the gauge set, 45psi was slightly low for the ambient temp, and 300psi was at the very high end of the normal range. It's been between 90-100F around here for the last week or so.

I've spent several days searching old posts here, and it seems all posts with my symptoms lead back to the same thing, low freon. Should I try to add another 1/4-1/2 can? Any and all suggestions would be much appreciated.

 

[merc80]

Any ideas as to what can cause the high pressure to be so high?

A little more info, most of the driving around here is state highways w/ a 55mph speed limit, with very few stops. There doesn't seem to be any correlation between speed and the a/c performance.

Thanks for the help so far.

 

[merc80]

One more thing...both the high and low pressure side ports leak with the cap off. Might that have anything to do with my problem?

 

[Turdle]

One more thing...both the high and low pressure side ports leak with the cap off. Might that have anything to do with my problem?

yup-
to change the valves though, you need to evacuate the system.

the valves are available at auto parts stores for a very small price. You remove them just like a tire valve-

 

[ma96782]

Check to see if your radiator fan clutch is operating correctly.

BTW......not knowing how much refrigerant you already have in there......IF YOU'RE ASSUMING YOU ARE LOW ON R-134a.......you could......continue to add refrigerant......mindful that too much is no good and too little is no good.......so, watch the pressure and temp readings. Checking your low side pressure and high side pressure against this pressure/temp chart.

System pressure/air temps chart (hi velocity fan in front of the condenser, engine running at 1500 RPM)

http://www.autoacforum.com/aacf/ptchart.cfm

The End Results............

Set the AC (max), doors closed and windows up, fan speed set at the fastest speed, 10 mins. running to stabilize the system. Check the ambient air temp and compare it w/ the vent temp. At an ambient air temp of 75-80 degrees F, you're looking for a 35-45 degrees F at the vent (about a 40 degree F difference, though close enough is good to).

Ambient air temps are taken 2” in front of the condenser. Vent temp is taken at the dash vent closest to the evaporator (usually one of the center vents).

Aloha, Mark

PS...........the Haynes book says ('95 Ford Explorer, Manual system)........at ambient air temp of 80 degrees F, hi velocity fan in front of the condenser, 1500 RPM.........22-50 low side and 160-250 high side pressure. Capacities: oil 7 oz and R-134a 1.63 lbs (26.08 oz)

 

[merc80]

jt, so the leaky valves could affect the compressor? I don't think it's leaking too bad with the caps on, it's held a charge for a few days now, low side pressure has stayed pretty consistent at 45psi. I'm not trying to argue, I'm just trying to understand. I've been seriouly considering evacuating to change out the orifice tube and possibly the accumulator anyway, so I might as well fix the valves. Are they a dealer only part or should most part stores carry them?

Mark, I can't find that chart in my Haynes manual. What section is it in?

Once again, thanks for all the good advice so far. I appreciate you guys taking the time to help me out.

 

[ma96782]

Hey guys my 1993 does not have fan infront of the condensor any recommendations on what to use?

The high speed fan I was talking about is your standard high velocity home shop fan. You set it to it's fastest speed, place it on top of a chair (or something), in front of the condenser, and let her rip. It helps to cool the condenser and engine down. Because after all, the car ain't moving and at 1500 RPMs it'll heat up fast.

Aloha, Mark

 

[ma96782]

Mark, I can't find that chart in my Haynes manual. What section is it in?

The chart is found on page 5-16

Haynes Techbook
Automotive Heating & Air Conditioning
2000 edition
________________________________________________________________

jt, so the leaky valves could affect the compressor?

Leaky valves, affect the system pressure, which in turn, affects the compressor operation.

About the valve, talk to a knowledgeable person at your NAPA store.

Story Time: Once when I was looking for the valve behind the accumulator's low pressure switch, the NAPA guy simply confirmed "low pressure." Went behind and came back with a schrader valve. He said the schrader valve is sort of generic......just have to know what pressures it'll be dealing with.

Now, that I said my story......I'm wondering, IF the valve's "rubber seals" are up to dealing with R-134a? Oh well.

Anyway, the other places I had tried before, only knew how to look for it in their computer........none of those others could find the part.

Aloha, Mark

PS.......FOR THOSE WITH AN R-12 SYSTEM......WARNING.....the Haynes book says that some mfns have gone to a "special high-side R-12 service valve." So, once evacuated, it'll probably be better to remove the valve(s).........place them into marked package(s) (high or low). Then, take them down to the NAPA store for a replacement.

 

[ma96782]

MadExplorer93,

About the book's chart of pressures/temps......

I was looking over the book and found a better troubleshooting section and chart, made of the FORD Fixed Orifice Tube system.......check it out.......beginning on page 6-28.

Aloha, Mark