A/C Diagnostics

To make a long story short, I reinstalled my a/c system last summer and after vacuuming / recharging it, it worked perfectly all summer. During the fall, I accidentally wiggled a line too much and ended up releasing the whole charge when the coupling slipped apart.

This summer, I figured it'd be as simple as putting another vacuum / recharge on the system to get her going again. It held 30" vacuum for a good couple of hours, so I put in a can of pag oil and then began charging the system. However....the compressor's clutch didn't come on at all, even after charging the system a bit past 30psi on the low pressure side.

I figured it might just be a bad pressure switch, so I jumped the harness and the compressor clicked on just fine. HOWEVER, there was absolutely no cold (or even cool) air coming from the vents. Any idea what might be going wrong now? It's already getting awfully warm this year, so I'd really like to have my a/c working [Image: smile.gif] Thanks for any input!

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Estoril blue 1987 TC 5spd, 142k miles, PRofec B, walbro 255 hi-pressure pump, Bailey BOV, rod's header, spearco FMIC, t3/t4 50 trim / stage III .63, full 3" exhaust, eec-tuner, 55pph injectors, Nitto 555R drag radials
Best 1/4 mile: 13.389

If you add to much oil you can lock-up the compressor. It can also oil log the evaporator and kill the systems performance. You don't looss that much oil when the refrigerant leaks out, It just looks like it. You should measure how much is left in it before you add it. You will know if the compressor is locked up if the clutch engages. Check for power to the clucth. If you have power and it doesn't engage then you have a bad clutch.

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85.5 TC 5 speed, Ranger Roller cam, 3" exhaust system, manual boost valve, large VAM, SVO PE computer, front mount Motorsport intercooler & sport grille, ported upper and lower intakes,flow matched injectors, ported E6 manifold, 245/45/17 wheels & Tires,140 mph speedo,Motorsport lowering springs, under restoration

How much more did you charge it after you got the thing to cycle.
in my ford a/c book, i think pressure has to be 47pis to kick ont eh clutch? correc tme if im wrong.
do you have a set of maifold guages ro just the one on the "topper" can?

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Brian J Larkin
1988 Turbo Coupe 5spd
dark blue metallic
gillis boost valve, k&n cone,AFPR, 255lph HP pump,3G 130amp alt, 3.73 gears,mild torquie cam, factory DP, 2003 mustang take off SS mufflers and custom BJL 2 1/4 tails.
(out os service due to my idiot self)

88 TC Auto, med gray met. raven/gray interior, fully loaded miuns leatehjr and sunroof!
converted to N/A 2.3l, but its a nice driver with working A/C!

Those low pressure switches can go bad.

Did you close the system back up right away after it intially lost it's charge? Any moisture in the system can ruin almost everything. Especially if it's left in there for a while.

If you had a sudden discharge of pressure, I bet you did loose most of your oil. It was a big mess right? I've been there before. One can should be okay, but too much can be bad too.

Double and triple check those quick release fittings (fuel lines too). They may seem connected, but actually not fully engaged.

You really should use gauges when you troubleshoot the AC. When you charge the system you should weigh-in the refrigerant. If you converted to R-134A or R414B you will use around 80% of the original charge. You will also loose around 10% of the cooling capacity.

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85.5 TC 5 speed, Ranger Roller cam, 3" exhaust system, manual boost valve, large VAM, SVO PE computer, front mount Motorsport intercooler & sport grille, ported upper and lower intakes,flow matched injectors, ported E6 manifold, 245/45/17 wheels & Tires,140 mph speedo,Motorsport lowering springs, under restoration

Brian - My Chilton's manual says the low pressure side should read between "5-20psi" once the system's been running and normalized....quite a wide variance if you ask me. I never did get the compressor to cycle, or even come on at all without having to jumper the pressure switch. I am using a set of actual A/C gauges/hoses.

Originally posted by TCorBUST:
Those low pressure switches can go bad.

Did you close the system back up right away after it intially lost it's charge? Any moisture in the system can ruin almost everything. Especially if it's left in there for a while.

If you had a sudden discharge of pressure, I bet you did loose most of your oil. It was a big mess right? I've been there before. One can should be okay, but too much can be bad too.

Double and triple check those quick release fittings (fuel lines too). They may seem connected, but actually not fully engaged.

Yeah, I reconnected the line within about 5 mins of when it blew apart. I had to spend those first 5 minutes hosing / washing / scrubbing all the oil off my forearms and half my engine bay [Image: frown.gif]

[This message has been edited by SteveX82 (edited 05-04-2004).]

Generally the low pressure cut out switch is gonna be open till the system is up to 30- 35 psi or so. Then it should hold unless pressure falls below 20 psi. Thats why a very low systen will cycle rapidly. Pressure will be high enough to close the switch, but as soon as the compressor starts pumping the low sie will drop to almost nothing. Compressor cuts out and the cycle repeats.

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Three 1988 Turbo Coupes .....
yea one of em has a 5.0 And runs 13.1s......
uhhh make that [email protected] with a 90hp shot of nitrous.