Pressure switches

[ma96782]

94 Explorer, 134a system...OK...today I got the A/C system to function (added about 20 oz of R134a)....if you remember:

http://www.explorerforum.com/forums/showthread.php?t=164634
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So, today I got: low pressure 45 and high pressure 225......vent temp 38.....ambient air temp 80. Sounds good......BUT, the problem is sometimes the compressor won't clutch "off" when it hits 225.

I guess it's a switch problem.

Do I change the switch on the accumulator or the switch on the muffler? I'm thinking -DANGEROUS- I should change the hi pressure switch (on the muffler?) Can someone confirm this?

Aloha, Mark

PS.....I bought the Harbor Freight Manifold set.....what a deal for the price.......hope it lasts.

 

[shamaal]

The clutch engagement switch on the accumulator kicks out at 24.5 psi and kicks in at 43.5 psi. The Ford system is a simple fixed orifice and does not have the sophisticated controls like other systems. There is no switch associated with the muffler.

The only switch on the high pressure side is on the back of the compressor hose fitting and is a pressure relief valve that only opens under abnormal circumstances (very high pressure).

 

[ma96782]

Thanks for the info....I picked up the switch (on the accumulator) for $20. Then I unscrewed the old switch and what do you know.......the valve behind the switch was leaking........by the time I got the new valve......all the R134a had escaped.

Back to the drawing board.....more R134a to buy ($6.88 per 12oz can) and vacuum the system.

Got all that done........and tried it again. NOTE to self: Sticker in the engine compartment says 1 lb. 8 oz of R-134a -Maximum.......WRONG, WRONG, WRONG......NAPA says 36 oz......can't really say how much I put in but after 24 oz. it was still warm........so, I released some (thought, maybe I over filled it) and then since it still wasn't getting cold, I added more and I kept adding, until I got.......Low pressure 30 and high pressure 250.....It was like 82-88 degrees (ambient air temp).......the lowest vent reading I got was 44 degrees.......but, the system liked to stay at about 50 degrees. I guess thats "good enough."

Aloha, Mark

PS....Next A/C project is the Chevy Pick Up.

 

[shamaal]

That's the second time I've heard of the schraeder valve sticking.

Next go at it, change the accumulator and the orifice (good practice) and evacuate for at least 45 minutes. Even 50 degrees feels good on a day like today.

 

[Glacier991]

For those reading, what Mark means is he evacuated the system, not vacuumed it. It is not a like vacuuming a carpet, but placing the system in a state of near complete vacuum to remove all air.

[I am promising myself to make this comment anytime I see someone say "vacuumed" because I think it is confusing to newbies.]

 

[ma96782]

shamaal,

Yes, the new accumulator and orifice tube will be on the list......after the Chevy project. I did the evacuation with my new pump I purchased off of e-bay.

Glacier991,

You're RIGHT (it is evacuated). I just got use to calling it "vacuum" cause when I went looking for a pump......it was listed as "vacuum pump." And, words like accumulator (vs. receiver dryer) and orifice tube (vs. expansion valve).......get's interchanged all the time. Even my shop guy gets the terms wrong at times......maybe I should have taken that as a hint?

For those looking for an economical pump.......check the the internet (the usual suspects).

Aloha, Mark

 

[ma96782]

Today, as I passed the bank (in my vehicle at 44 degrees).....the sign said it was 86 degrees outside........gee, I'm happy now.

And, now that I have had time to reflect on this project......I figure it's FORD's fault. The sticker in the engine compartment said MAXIMUM 1 lb. 8 oz. (24 oz)......it never got cold. The shop was doing what the sticker said (so, perhaps, that was the main reason). IF, the shop followed the book or NAPA (both said 36 oz.)......I may have gotten the joy I was seeking. Not to mention, the shop guy only evacuated the system until it just hit 29. Now, after reading, I know why it needs to be done for a longer period of time. Though, in the end, the FORD engineer responsible, should get a big kick in the b*^^ for that mistake (and quick detach fittings, on the fuel and AC lines).

All in all, another good reason to DIY (if you're willing to shell out for the tools).

Aloha, Mark

 

[Glacier991]

Good going Mark.

ps. I wasn't being critical with my vacuum comment. Lotsa newbies here and that is one thing tht sometimes confuses them...

pps. And I often interchange the terms receiver/dryer and accumulator and orifice tube and expansion valve as well.