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AC shuts down when on the gas, check engine light on.

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I have had a new (to me) 1989 LX 5.0 for about a month and a half now. When I got it the AC worked fine. I had a new AOD transmission put in it a few weeks ago and immediately the check engine light came on. The transmission shop said that they saw it and checked it and it was "an EGR code."

I disconnected the battery and I replaced the EGR valve. The EGR sensor seems fine as it moves freely. The check engine light is still on though.

At the same time I've noticed that when I get on the gas, as when passing or going up a hill or just for giggles, the air blows much warmer out of the vents and the air blows much more slowly. I drove up a large hill in my neighborhood today and the air shut off completely. Once I got off the gas, the AC came roaring back on and the air which came out was very cold.

Any ideas if the two issues (engine light and wonky AC performance) are related? Or what it could be?

I bought the car expecting to have to do some work on it but I've already done new rack and pinion and new transmission. The bride is starting to raise an eyebrow, and if this is a quick fix I'd rather do it myself then take it back to the shop.

Thanks!

Reply to
Thomas Cameron
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I don't think there are any codes for the AC. Independent systems. What is the code? the EGR system is composed of a lot of items, and a few very small vacuum hoses, check them for cracks, I had one crack one on the 93 5.0. The way the AC is weak is very strange, could be the AC clutch is slipping, but usually they just break. I killed one at high RPM about 6 grand, with the AC on, and it busted the AC clutch. The fan takes a lot of current on HI setting, and a voltage drop, going up hill would slow it down as the voltage is lower, or sag, however getting on the gas make the voltage OK. Was the fan still going strong on the large hill, but AC not cold?

Reply to
Dear Leader

You've got either a vacuum leak or the one-way valve in the line to the vacuum canister is bad. What's happening is that when you get on it the engine vacuum drops from 19" to single digits. When that happens the vacuum operated doors in the ac system all move to their "off" position, which is basically to blow air out the heater and defrost vents. So it seems like the AC is shutting down. Since as soon as you get off it the air is cold I don't think you have any actual AC system problems, just the vacuum issue. It's possible someone took the one-way valve out if they didn't know what it was.

It is very unlikely that there is a connection between the AC issue and the CELight.

Reply to
Ashton Crusher

there is a small rubber elbow hose at the canister which expands and degrades and gets too big to stay on, on 5.0s, no new replacements, but you can use other rubber hoses and adapters to replace it. passenger side way up front on the low part of the frame

Reply to
Dear Leader

Are you flooring the pedal? The AC is supposed to cut out at WOT so all the engine's power goes to the rear wheels. Sounds like normal operation to me.

Go have the code scanned and get the number(s). There are several people here who can point you in the right direction given the proper detail.

Arlie

1989 Mustang LX 5.0 Fastback 1992 Thunderbird LX 5.0
Reply to
Blue Gator

This is normal operation for the AC, when the car is under load the CPU disengages the AC clutch when you romp on the gas to free up some more HP. As for the check engine light, get a cheap code reader and dump the codes. Remember just because the code reader says a sensor is detecting an error out doesn't mean that the sensor is bad, it could mean that the parameter that it was measuring is out of limits and you might actually have something broken.

Reply to
Ironrod

Terribly sorry for the delay in answering. Many thanks for all the answers.

Turns out there is a little one-way vacuum valve on the passenger side firewall, and it was leaking. I went to the local AutoZone and they had a replacement for $3.99 or so. Easy as pie.

I am still having an issue with the CE light coming on but will post that separately.

Thomas

Reply to
Thomas Cameron

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