Question A/C not cooling only at cruising speed

[DieselDo]

Got a question on the A/C system, running it coming from work this afternoon, I was getting warm air out of the vents while on the highway. Once I got into slower stop and go type traffic it started cooling well. Got it home and popped the hood and at idle and lower rpm compressor stays engaged, at higher rpm around 1500, compress starts cycling every few seconds.

any thoughts?

 

[BIG JOE]

Look'n under the hood from the grille. Try this:

Just behind and to the left of the A/C compressor.. yul see the A/C pressure switch. If with the A/C on.. if you can engage/disengage the clutch by wiggling that connector.. take the connector apart and clean the pins. Grit, grime and corrosion/condensation gets to that connector over time ?

Joe

I tweaked the pins a bit.. for a tighter fit.. and lightly sealed the connector with RTV ?

You might want to check your Freon level too ?

 

[DaveBen]

Low freon will cause the clutch to cycle rapidly. But the cooling at lower speeds tells me that the freon is good. When was the AC last checked? Might be time to do it again.

Dave

 

[JLDickmon]

Without putting pressure gauges on it, it's hard to tell.
Almost sounds like you have two problems, really.
Know anyone with a manifold gauge set?

 

[DieselDo]

Joe,
Tried the wiggle test, all check out o.k. compressor never disengaged.

DaveBen:
by checked do you mean serviced? if so, to my knowledge, never. This is the first time it's had an issue and has only been in the shop for a water pump and a rebuilt trans. A gauge manifold was hooked up once by me to check gauge operation something like 3 years ago.

JLD:
I have a set of 134a gauges from back in my mechanic days, never really learned how to use them right. If reading would be helpful, I can probably hook them up this weekend. What was your thinking on the problems?

 

[JLDickmon]

Yeah. That would be.
Take high & low side readings at
1. Idle
2. 1500rpm

I'm thinking you have a dirty orfice tube (rapid cycling), and maybe a bad clutch (no cooling at high rpm)

 

[DieselDo]

gauge readings @ 78 degrees F ambient, fan control on max, function to max A/C

static pressure 78 psig

idle test:
low side compress engages at 40psig, disengaged at 20 psgi
high side engages at 100 psig, disengages at 125 psig

1500 RPM
low side, engages at 40 psig, disengages at 22 psig
high side, engages at 105 psig, disengages at 125 psig

when un hooking test gauges, I noticed a neon green oily substance. Leak tracer installed by the previous owner?

 

[JLDickmon]

Ok.. Now we're getting somewhere...
First things first, it's low on charge.
High side pressure should be more or less 200 psi at 1500 rpm.
We'll worry about low side when we see if e can get the high side up.

And yes, the green stuff is likely dye.

 

[DieselDo]

The neon green was definately leak tracer, it glowed under UV light. The good news, I cant find any signs of a leak. so if it is, it must be very small to take 14 years to show up. First chance I get I'll add a few ounces and see if I cant get the pressures up.

 

[JLDickmon]

The neon green was definately leak tracer, it glowed under UV light. The good news, I cant find any signs of a leak. so if it is, it must be very small to take 14 years to show up. First chance I get I'll add a few ounces and see if I cant get the pressures up.

You're probably talking pounds.. Get a couple hand grenades from Advance..