Automotive Air Conditioning Information Forum

Hello,

This is a truck that my father purchased used, back in the late 1990's. Between then and now, nothing has been done with the AC system. It always used to blow icicles...now not so much. Started noticing the drop in cooling performance in about the last year or so.

Recently, I bought R12 gauges and took pressure readings:

1993 Ford-F150 4.9L 6-cylinder engine
Refrigerant: R12
Pressure readings taken at idle:
Ambient temperature: 84 deg f
High side: 245
Low side: 48
Vent temperature: 60 deg f

Since the system hasn't been touched in ages, if ever, I was originally thinking the system might be low on refrigerant. While that may be the case, I'm surprised that the low-side is as high as it is. I did touch the evaporator inlet and outlet pipes. The inlet on the bottom is significantly colder than the outlet on the top. The compressor wasn't cycling at all.

Needless to say, I'm not an expert on this, don't do this for a living, and this is the first R12 system that I've ever looked at. I'd be Interested in hearing peoples opinions before going any further with this.

You need to check to make sure that heated air is not being introduced to the air flow.

The rpm at idle is not high enough. Run the engine at 1500 rpm. The high side appears high; it may need a new fan clutch. Run the engine up, mist the condenser with water. If the high side drops, you have air flow problems across condenser. The system may also be low on refrigerant indicating multiple problems.

High side @ 245 with an ambient of 84? Condensing problem.
Check the air path through the condenser for debris. Clean the condenser and radiator exterior, be careful not to bend the fins. Us a strong soap like simple green, spray it deep in to the fins - and rinse it out with a garden hose. Avoid high pressure washers, you can bend the fins with one of those in a heartbeat.

On my '93 F150 I find it easiest to remove the grill for that job.

The fan clutch is probably shot. They wear out. You will need the two magic wrenches to change it Usually the parts store has loaners. There are two different fan clutch threads on the 4.9 in that model range. Take the old one off & wash your hands. Then unbox the new one & compare it - the difference is obvious.

Is this dealer installed A/C or OEM A/C? Dealer A/C will have a Sanden 7H15 compressor installed low, under the power steering pump on the driver's side.

Thanks for all of the replies.

Cusser wrote:You need to check to make sure that heated air is not being introduced to the air flow.

It's possible that a little bit of heat could be leaking through. Warmed up the truck and my car and stuck thermometers in the vents. On the car it was 85 deg f; the truck was 90 deg f. May consider putting a shutoff valve on the heater hoses, at some point.

bohica2xo wrote:High side @ 245 with an ambient of 84? Condensing problem.
Check the air path through the condenser for debris. Clean the condenser and radiator exterior, be careful not to bend the fins. Us a strong soap like simple green, spray it deep in to the fins - and rinse it out with a garden hose

Sounds like a good place to start: simple green and a garden hose. Have both of those already.

bohica2xo wrote:Is this dealer installed A/C or OEM A/C? Dealer A/C will have a Sanden 7H15 compressor installed low, under the power steering pump on the driver's side.

The compressor is under the power steering pump, on the driver's side. Was hoping to find a label on it, but didn't see one.

Adding the fan clutch to my to-do list, too.