A/C turning off when my foot is on the petal

[83countrysquire]

So got it converted from r12 to r134a and the a/c was freezing. But today i went for a drive to get it inspected and i noticed that when i go more than quarter throttle that the a/c turns off into heat but than when i reach my desired speed it turns back on to freezing air. What could be causing this?

[87vicFIVEO]

Is it overcharged?

IF the pressure is too high, the system will shut off when engine rpm goes up, to procect itself.

When you convert r12 - r134a you should charge the system with 80% of the recommended r12 charge.

In your car 54 ounces is the recommended r12 charge.

SO for 134a you should charge it with 43 ounces of 134a.

I'd be willing to bet that's your problem, fix it before you blow a line or your condenser!

[turbo2256b]

You might have a vacuum leak somewere or a bad vacuum door motor.

[gadget73]

vacuum leak in the climate control system. Classic problem. It defaults to hot defrost in the event of a vacuum loss. Check the soup can for rot and check for a cracked line to it, or to the thermal blower lockout if you have one. You'll only have one if its ATC, it'll be in one of the heater hoses.

[turbo2256b]

I remember finding a rust hole in the vacuum can on my blue Merc pluged it started the car and watched as the can collapsed.

Check the emergency brake release horse shoe at the base of the steering columb

[87vicFIVEO]

I assumed his hot air was blowing out of the vents.

[gadget73]

I should also mention there is a wide open cutout relay, so if you're jamming the pedal to the floor, the AC will shut off, but that only happens over like 7/8 throttle or something. The vacuum temperature mess only happens on cars with auto climate control. Manual climate control doesn't have that problem. It will only shift where it comes from.

[87vicFIVEO]

Pay attention during acceleration, or rev the motor in park....see if you can hear the A/C compressor clutch Engaging and Dis-engaging.

If it's "short cycling" it's probably a pressure issue (high or low charge).

[gabegt90]

yeah mine does the same. when going up hill etc I'm just used to it

[gadget73]

mine used to do that. Soup can was bad and it leaked at the TBL. $26 at the dealer for a new one, and I removed the TBL and it stopped changing on hills, etc. My interior temperature sensor also went bad so the temperature was unstable, replaced that as well. I actually have stable temperature control now. Its actually pretty impressive how well it actually does work with new parts given how rinky dinky the whole system is. The more modern electronic controls are a lot more accurate, but they have electronic blend door problems and all sorts of other issues. After 20 years having to invest $75 an an hour or so of time to repair it seems reasonable.

[83countrysquire]

well the soup can is fine and i dont know how to check the other lines and arent sure which ones are vaccum

[Lincolnmania]

theres a vacuum routing diagram under the hood

[87lxcoupe]

I had this EXACT same problem. After pressure testing the can, and checking the whole under-dash system, it turned out to be the A/C vacuum control valve (located behind the engine, running off of the vacuum block mounted on the firewall). I actually bought a brand new control valve from my local dealer, but after installing it, still had the same problem. To make a long story short, it turns out the "new" control valve was defective. A second, new valve fixed the problem. All it is, is an F-shaped vacuum fitting with a check-ball inside. If you need the part number it's #D9AZ-19A563-AA. Ford's price was $7.60. Hope this helps ya!
BTW, if you happen to want a new vacuum can, the part # is E1VY-19A566-A for cars with Climate Control (I ended up buying one of these too, just for insurance). The list price for the can is $30.98. Got mine for $25.

[1987cp]

You shouldn't be stepping on petals; they're kind of delicate. You should dry them between the pages of a book and save them for posterity.